Pharmacokinetic and Pharmacodynamic Comparison of Once-Daily Efavirenz (400 mg vs. 600 mg) in Treatment-Naïve HIV-Infected Patients: Results of the ENCORE1 Study

Individualizing Antiretroviral Therapy in the Older Patient

Owing to widespread availability of potent and tolerable antiretroviral therapy, life expectancy of people with human immunodeficiency virus (HIV) has significantly increased. Consequently, the population of people with HIV are ageing, with over 50% over the age of 50 years, and it is expected that 25% will be over the age of 65 years by 2030. People diagnosed with HIV at older age tend to have more advanced disease, and may already be experiencing comorbidities that will influence the choice of initial antiretroviral treatment. Despite the well described changes in pharmacokinetics associated with ageing, there are a paucity of pharmacokinetics studies of contemporary antiretroviral drugs to help guide treatment for HIV. Irrespective of this, integrase inhibitor-based regimens have been shown to have similar treatment outcomes in older and young adults and are the preferred regimens for initiation and switching therapy in older adults. Non-acquired immunodeficiency syndrome (AIDS) comorbidities are more common in people with HIV owing to chronic immune activation and inflammation even in the presence of virological suppression on antiretroviral treatment. Screening and risk assessment of comorbidities is crucial as the presence of geriatric syndrome, frailty or neurocognitive impairment may impact medication adherence. Simplification of complex regimens, both antiretroviral and comorbidity treatments, is recommended to improve adherence. Regular medication reviews under the guidance of an experienced HIV pharmacist are recommended to identify adverse drug-drug interactions and inappropriate prescribing of drugs with potential adverse effects, such as falls risk. Antiretroviral stewardship has been shown to improve patient outcomes and quality of life for ageing people with HIV.

Determining Targets for Antiretroviral Drug Concentrations: A Causal Framework Illustrated With Pediatric Efavirenz Data From the CHAPAS-3 Trial

BACKGROUND

Determining a therapeutic window for maintaining antiretroviral drug concentrations within an appropriate range is required for identifying effective dosing regimens. The limits of this window are typically calculated using predictive models. We propose that target concentrations should instead be calculated based on counterfactual probabilities of relevant outcomes and describe a counterfactual framework for this.

METHODS

The proposed framework is applied in an analysis including longitudinal observational data from 125 HIV-positive children treated with efavirenz-based regimens within the CHAPAS-3 trial, which enrolled children < 13 years in Zambia/Uganda. A directed acyclic graph was developed to visualize the mechanisms affecting antiretroviral concentrations. Causal concentration-response curves, adjusted for measured time-varying confounding of weight and adherence, are calculated using g-computation.

RESULTS

The estimated curves show that higher concentrations during follow-up, 12/24 h after dose, lead to lower probabilities of viral failure (> 100 c/mL) at 96 weeks of follow-up. Estimated counterfactual failure probabilities under the current target range of 1-4 mg/L range from 24% to about 2%. The curves are almost identical for slow, intermediate and extensive metabolizers and show that a mid-dose concentration level of ≥ 3.5 mg/L would be required to achieve a failure probability of < 5%.

CONCLUSIONS

Our analyses demonstrate that a causal approach may lead to different minimum concentration limits than analyses that are based on purely predictive models. Moreover, the approach highlights that indirect causes of failure, such as patients' metabolizing status, may predict patients' failure risk, but do not alter the threshold at which antiviral activity of efavirenz is severely reduced.

PBPK Modeling of Lamotrigine and Efavirenz during Pregnancy: Implications for Personalized Dosing and Drug-Drug Interaction Management

This study aimed to model the pharmacokinetics of lamotrigine (LTG) and efavirenz (EFV) in pregnant women using physiologically based pharmacokinetic (PBPK) and pregnancy-specific PBPK (p-PBPK) models. For lamotrigine, the adult PBPK model demonstrated accurate predictions for pharmacokinetic parameters. Predictions for the area under the curve (AUC) and peak plasma concentration (Cmax) generally agreed well with observed values. During pregnancy, the PBPK model accurately predicted AUC and Cmax with a prediction error (%PE) of less than 25%. The evaluation of the EFV PBPK model revealed mixed results. While the model accurately predicted certain parameters for non-pregnant adults, significant discrepancies were observed in predictions for higher doses (600 vs. 400 mg) and pregnant individuals. The model's performance during pregnancy was poor, indicating the need for further refinement to account for genetic polymorphism. Gender differences also influenced EFV pharmacokinetics, with lower exposure levels in females compared to males. These findings highlight the complexity of modeling EFV, in general, but specifically in pregnant populations, and the importance of validating such models for accurate clinical application. The study highlights the importance of tailoring dosing regimens for pregnant individuals to ensure both safety and efficacy, particularly when using combination therapies with UGT substrate drugs. Although drug-drug interactions between LTG and EFV appear minimal, further research is needed to improve predictive models and enhance their accuracy.

A Physiologically-Based Pharmacokinetic Simulation to Evaluate Approaches to Mitigate Efavirenz-Induced Decrease in Levonorgestrel Exposure with a Contraceptive Implant

Background: Levonorgestrel implant is a highly effective hormonal contraceptive, but its efficacy may be compromised when used with cytochrome enzyme inducers such as efavirenz. The primary aim of this study was to evaluate methods of mitigating the drug interaction. Methods: Using a physiologically-based pharmacokinetic (PBPK) model for levonorgestrel that we developed within the Simcyp® program, we evaluated a higher dose of levonorgestrel implant, a lower dose of efavirenz, and the combination of both, as possible methods to mitigate the interaction. In addition, we investigated the impact on levonorgestrel total and unbound concentrations of other events likely to be associated with efavirenz coadministration: changes in plasma protein binding of levonorgestrel (as with displacement) and high variability of efavirenz exposure (as with genetic polymorphism of its metabolism). The range of fraction unbound tested was 0.6% to 2.6%, and the range of efavirenz exposure ranged from the equivalent of 200 mg to 4800 mg doses. Results: Levonorgestrel plasma concentrations at any given time with a standard 150 mg implant dose are predicted to be approximately 68% of those of control when given with efavirenz 600 mg and 72% of control with efavirenz 400 mg. With double-dose levonorgestrel, the predictions are 136% and 145% of control, respectively. A decrease in levonorgestrel plasma protein binding is predicted to primarily decrease total levonorgestrel plasma concentrations, whereas higher efavirenz exposure is predicted to decrease total and unbound concentrations. Conclusions: Simulations suggest that doubling the dose of levonorgestrel, particularly in combination with 400 mg daily efavirenz, may mitigate the drug interaction. Changes in levonorgestrel plasma protein binding and efavirenz genetic polymorphism may help explain differences between model predictions and clinical data but need to be studied further.

Total and Free Blood and Plasma Concentration Changes in Pregnancy for Medicines Highly Bound to Plasma Proteins: Application of Physiologically Based Pharmacokinetic Modelling to Understand the Impact on Efficacy

Free drug concentrations are generally considered the pharmacologically active moiety and are important for cellular diffusion and distribution. Pregnancy-related changes in plasma protein binding and blood partitioning are due to decreases in plasma albumin, alpha-1-acid glycoprotein, and haematocrit; this may lead to increased free concentrations, tissue distribution, and clearance during pregnancy. In this paper we highlight the importance and challenges of considering changes in total and free concentrations during pregnancy. For medicines highly bound to plasma proteins, such as tacrolimus, efavirenz, clindamycin, phenytoin, and carbamazepine, differential changes in concentrations of free drug during pregnancy may be clinically significant and have important implications for dose adjustment. Therapeutic drug monitoring usually relies on the measurement of total concentrations; this can result in dose adjustments that are not necessary when changes in free concentrations are considered. We explore the potential of physiologically based pharmacokinetic (PBPK) models to support the understanding of the changes in plasma proteins binding, using tacrolimus and efavirenz as example drug models. The exposure to either drug was predicted to be reduced during pregnancy; however, the decrease in the exposure to the total tacrolimus and efavirenz were significantly larger than the reduction in the exposure to the free drug. These data show that PBPK modelling can support the impact of the changes in plasma protein binding and may be used for the simulation of free concentrations in pregnancy to support dosing decisions.

Decreased Dolutegravir and Efavirenz Concentrations With Preserved Virological Suppression in Patients With Tuberculosis and Human Immunodeficiency Virus Receiving High-Dose Rifampicin

BACKGROUND

Higher doses of rifampicin may improve treatment outcomes and reduce the duration of tuberculosis (TB) therapy. However, drug-drug interactions with antiretroviral therapy (ART) and safety in people with human immunodeficiency virus (HIV) have not been evaluated.

METHODS

This was a randomized, open-label trial where newly diagnosed TB patients were randomized to higher (35 mg/kg) or standard (10 mg/kg) daily-dose rifampicin. ART treatment-naive patients were randomized to dolutegravir- or efavirenz-based ART. At week 6, trough dolutegravir or mid-dose efavirenz plasma concentrations were assayed. HIV viral load was measured at week 24.

RESULTS

Among 128 patients randomized, the median CD4 count was 191 cells/mm3. The geometric mean ratio (GMR) for trough dolutegravir concentrations on higher- vs standard-dose rifampicin was 0.57 (95% confidence interval [CI], .34-.97; P = .039) and the GMR for mid-dose efavirenz was 0.63 (95% CI, .38-1.07; P = .083). There was no significant difference in attainment of targets for dolutegravir trough or efavirenz mid-dose concentrations between rifampicin doses. The incidence of HIV treatment failure at week 24 was similar between rifampicin doses (14.9% vs 14.0%, P = .901), as was the incidence of drug-related grade 3-4 adverse events (9.8% vs 6%). At week 8, fewer patients remained sputum culture positive on higher-dose rifampicin (18.6% vs 37.0%, P = .063).

CONCLUSIONS

Compared with standard-dose rifampicin, high-dose rifampicin reduced dolutegravir and efavirenz exposures, but HIV suppression was similar across treatment arms. Higher-dose rifampicin was well tolerated among people with HIV and associated with a trend toward faster sputum culture conversion.

CLINICAL TRIALS REGISTRATION

NCT03982277.

Efavirenz: History, Development and Future

Efavirenz (Sustiva^®) is a first-generation non-nucleoside reverse transcriptase inhibitor (NNRTI) used to treat human immunodeficiency virus (HIV) type 1 infection or to prevent the spread of HIV. In 1998, the FDA authorized efavirenz for the treatment of HIV-1 infection. Patients formerly required three 200 mg efavirenz capsules daily, which was rapidly updated to a 600 mg tablet that only required one tablet per day. However, when given 600 mg once daily, plasma efavirenz concentrations were linked not only to poor HIV suppression but also to toxicity. Clinical data suggested that the standard dose of efavirenz could be reduced without compromising its effectiveness, resulting in a reduction in side effects and making the drug more affordable. Therefore, ENCORE1 was performed to compare the efficiency and safeness of a reduced dose of efavirenz (400 mg) with the standard dose (600 mg) plus two NRTI in antiretroviral-naïve HIV-infected individuals. Nowadays, due to the emergence of integrase strand transfer inhibitors (INSTIs), some consider that it is time to stop using efavirenz as a first-line treatment on a global scale, in the parts of the world where that is possible. Efavirenz has been a primary first-line antiviral drug for more than 15 years. However, at this moment, the best use for efavirenz could be for pre-exposure prophylaxis (PrEP) and repurposing in medicine.

Predictors of Efavirenz Plasma Exposure, Auto-Induction Profile, and Effect of Pharmacogenetic Variations among HIV-Infected Children in Ethiopia: A Prospective Cohort Study

(1) Background: Efavirenz plasma concentration displays wide between-patient variability partly due to pharmacogenetic variation and autoinduction. Pediatric data on efavirenz pharmacokinetics and the relevance of pharmacogenetic variation are scarce, particularly from sub-Saharan Africa, where >90% of HIV-infected children live and population genetic diversity is extensive. We prospectively investigated the short- and long-term effects of efavirenz auto-induction on plasma drug exposure and the influence of pharmacogenetics among HIV-infected Ethiopian children. (2) Method: Treatment-naïve HIV-infected children aged 3-16 years old (n = 111) were enrolled prospectively to initiate efavirenz-based combination antiretroviral therapy (cART). Plasma efavirenz concentrations were quantified at 4, 8, 12, 24, and 48 weeks of cART. Genotyping for CYP2B6, CYP3A5, UGT2B7, ABCB1, and SLCO1B1 common functional variant alleles was performed. (3) Results: The efavirenz plasma concentration reached a peak at two months, declined by the 3rd month, and stabilized thereafter, with no significant difference in geometric mean over time. On average, one-fourth of the children had plasma efavirenz concentrations ≥4 µg/mL. On multivariate analysis, CYP2B6*6 and ABCB1c.3435 C > T genotypes and low pre-treatment low-density lipoprotein (LDL) were significantly associated with higher plasma efavirenz concentration regardless of treatment duration. Duration of cART, sex, age, nutritional status, weight, and SLCO1B, CYP3A5, UGT2B7, and ABCB1 rs3842 genotypes were not significant predictors of efavirenz plasma exposure. (4) Conclusion: Pre-treatment LDL cholesterol and CYP2B6*6 and ABCB1c.3435 C > T genotypes predict efavirenz plasma exposure among HIV-infected children, but treatment-duration-dependent changes in plasma efavirenz exposure due to auto-induction are not statistically significant.

Therapeutic drug monitoring study on the switch from coformulated 600-mg efavirenz, tenofovir disoproxil fumarate, and emtricitabine to coformulated 400-mg efavirenz, tenofovir disoproxil fumarate, and lamivudine among HIV-positive patients with viral suppression

OBJECTIVES

This study evaluated the efavirenz (EFV) mid-dose plasma concentration (C12), clinical efficacy, and safety after the switch to a single-tablet regimen containing tenofovir disoproxil fumarate (TDF), lamivudine (3TC), and 400-mg EFV in virally suppressed HIV-positive Taiwanese who were receiving co-formulated TDF, emtricitabine (FTC), and 600-mg EFV.

METHODS

In this single-arm, open-label study, HIV-positive adults who had undetectable plasma HIV RNA load (<50 copies/ml) for 6 months or longer while receiving co-formulated TDF, FTC, and 600-mg EFV with EFV C12 of ≥1 mg/L were enrolled. The participants were switched to co-formulated TDF, 3TC, and 400-mg EFV and followed for 24 weeks. The primary endpoint was the proportion of participants with EFV C12 ≥ 1 mg/L at Week 4. The secondary endpoints included virologic response and change of CD4 lymphocyte count up to Week 24. Specific adverse effects associated with EFV were recorded before and after the switch.

RESULTS

From December 2018 to January 2019, 50 participants were enrolled. EFV C12 remained ≥1 mg/L in 48 (96.0%) participants with a median reduction of 38.9% (interquartile range 29.0-44.4) at Week 4 after switch. All participants had undetectable plasma HIV RNA by Week 12, whereas 96.0% of them remained so at Week 24. Significant increases of CD4 lymphocyte count were observed at Weeks 12 and 24. Thirty-three participants (66.0%) reported improvement of pre-existing adverse effects.

CONCLUSION

Switch to coformulated TDF, 3TC, and 400-mg EFV in virally suppressed HIV-positive Taiwanese maintained effective EFV concentration and viral suppression while the adverse effects were reduced.

Pharmacokinetics of Ruxolitinib in HIV Suppressed Individuals on Antiretroviral Agent Therapy from the ACTG A5336 Study

Ruxolitinib is a US Food and Drug Administration-approved orally administered Janus kinase (1/2) inhibitor that reduces cytokine-induced inflammation. As part of a randomized, phase 2, open-label trial, ruxolitinib (10 mg twice daily) was administered to HIV-positive, virologically suppressed individuals (33 men, 7 women) on antiretroviral therapy (ART) for 5 weeks. Herein, we report the population PK subsequently determined from this study. Plasma concentrations of ruxolitinib (294 samples) and antiretroviral agents were measured at week 1 (N = 39 participants) and week 4 or 5 (N = 37). Ruxolitinib PK was adequately described with a 2-compartment model with first-order absorption and elimination with distribution volumes normalized to mean body weight (91.5 kg) and a separate typical clearance for participants administered efavirenz (a known cytochrome P450 3A4 inducer). Participants administered an ART regimen with efavirenz had an elevated typical apparent oral clearance versus the integrase inhibitor regimen group (22.5 vs 12.9 L/hr; N = 14 vs 25). Post hoc predicted apparent oral clearance was likewise more variable and higher (P < .0001) in those administered efavirenz. There was  an ≈25% variation in ruxolitinib plasma exposures between week 1 and week 4/5. ART plasma concentrations resembled those from PK studies without ruxolitinib. Therefore, integrase inhibitor-based ART regimens may be preferred over efavirenz-based regimens when ruxolitinib is administered to HIV-positive individuals.

Effect of high-dose rifampicin on efavirenz pharmacokinetics: drug-drug interaction randomized trial

BACKGROUND

High-dose rifampicin is considered to shorten anti-TB treatment duration but its effect on antiretroviral metabolism is unknown.

OBJECTIVES

To assess the effect of doubling the rifampicin dose (to 20 mg/kg/day, R20) on efavirenz pharmacokinetics (PK) in HIV/TB coinfected patients.

METHODS

Open-label Phase 2 drug-drug interaction randomized trial. Pulmonary TB, ART-naive adults were randomized to R20 and either efavirenz 600 mg (EFV600) or 800 mg (EFV800), or rifampicin 10 mg/kg/day (R10) and EFV600 with a 1:1:1 ratio. Patients were first started on TB treatment and 2-4 weeks later started on ART. They were switched to R10 and EFV600 after 8 weeks. Full PK sampling was done 4 weeks (on rifampicin) and 24 weeks (off rifampicin) after ART initiation. Transaminases, plasma HIV-1 RNA and sputum cultures were monitored. The efavirenz geometric mean ratio (GMR) of AUC at 4 and 24 weeks after ART initiation within the same patient was calculated in each arm and its 90% CI was compared with a preset range (0.70-1.43).

RESULTS

Of 98 enrolled patients (32 in the R20EFV600 arm, 33 in the R20EFV800 arm and 33 in the R10EFV600 arm), 87 had full PK sampling. For the R20EFV600, R20EFV800 and R10EFV600 arms, GMRs of efavirenz AUC were 0.87 (90% CI: 0.75-1.00), 1.12 (90% CI: 0.96-1.30) and 0.96 (90% CI: 0.84-1.10). Twelve weeks after ART initiation, 78.6%, 77.4% and 72.4% of patients had HIV-1 RNA below 100 copies/mL and 85.7%, 86.7% and 80.0% had Week 8 culture conversion, respectively. Two patients per arm experienced a severe increase in transaminases.

CONCLUSIONS

Doubling the rifampicin dose had a small effect on efavirenz concentrations and was well tolerated.

Therapeutic Drug Monitoring of HIV Antiretroviral Drugs in Pregnancy: A Narrative Review

To date, therapeutic drug monitoring (TDM) has played an important role in the management of pregnant HIV patients on highly active antiretroviral therapy. Historically, in pregnant women living with HIV, the third agent in triple therapy has been either non-nucleoside reverse transcriptase inhibitors or protease inhibitors (PIs). PIs have been the preferred agents because of their robustness from the perspective of viral resistance and the dominant drug class for the management of HIV during pregnancy for the previous decade. As with many drugs used during pregnancy, pharmacokinetic changes decrease exposure to these agents as the pregnancy progresses. This can lead to viral escape at the time of pregnancy and ultimately increase the risk of mother-to-child transmission (MTCT) of HIV. TDM has been well-established for this class of highly active antiretroviral therapy, and appropriate dose adjustment studies have been performed. At present, there is a shift from the traditional treatment paradigm in pregnancy to a new drug class, integrase strand transfer inhibitors (INSTIs). Although INSTIs are affected by pharmacokinetic changes during pregnancy, they do not harbor the same issues with viral escape as seen with PIs at birth and in general eliminate the need for boosting with additional agents like ritonavir (r) and cobicistat (c) [bar elvitegravir (EVG)] that can lead to interactions with treatment of other common infections in HIV, including tuberculosis. Furthermore, INSTIs are the most successful medication for rapidly reducing the viral load (VL) in HIV patients, a useful factor where VL may be unknown, or in late presenters. These merits make INSTIs the best choice in pregnancy, although their use has been hindered in recent years by a report of neural tube defects from a large African study with dolutegravir (DTG). New data from Botswana and Brazil indicate that this risk is less significant than previously reported, necessitating further data to shed light on this critical issue. Current international guidelines including DHHS, EACS, WHO, and BHIVA (for patients with VLs >100,000 copies/mL or late presenters) now recommend INSTIs as first-line agents. The role of TDM in INSTIs shifts to cases of insufficient viral suppression with standard adherence measures, cases of drug-drug interactions, or cases where EVG/c is continued throughout pregnancy, and thus remains an important aspect of HIV care in pregnancy.

Pharmacokinetics and Drug-Drug Interactions of Isoniazid and Efavirenz in Pregnant Women Living With HIV in High TB Incidence Settings: Importance of Genotyping

The World Health Organization guidelines recommend that individuals living with HIV receive ≥ 6 months of isoniazid preventive therapy, including pregnant women. Yet, plasma isoniazid exposure during pregnancy, in the antiretroviral therapy era, has not been well-described. We investigated pregnancy-induced and pharmacogenetic-associated pharmacokinetic changes and drug-drug interactions between isoniazid and efavirenz in pregnant women. Eight hundred forty-seven women received isoniazid for 28 weeks, either during pregnancy or at 12 weeks postpartum, and 786 women received efavirenz. After adjusting for NAT2 and CYP2B6 genotype and weight, pregnancy increased isoniazid and efavirenz clearance by 26% and 15%, respectively. Isoniazid decreased efavirenz clearance by 7% in CYP2B6 normal metabolizers and 13% in slow and intermediate metabolizers. Overall, both isoniazid and efavirenz exposures were reduced during pregnancy, but the main determinants of drug concentration were NAT2 and CYP2B6 genotypes, which resulted in a five-fold difference for both drugs between rapid and slow metabolizers.

PharmVar GeneFocus: CYP2B6

The Pharmacogene Variation Consortium (PharmVar) catalogs star (*) allele nomenclature for the polymorphic human CYP2B6 gene. Genetic variation within the CYP2B6 gene locus impacts the metabolism or bioactivation of clinically important drugs. Of particular importance are efficacy and safety concerns regarding: efavirenz, which is used for the treatment of HIV type-1 infection; methadone, a mainstay in the treatment of opioid use disorder and as an analgesic; ketamine, used as an antidepressant and analgesic; and bupropion, which is prescribed to treat depression and for smoking cessation. This GeneFocus provides a comprehensive overview and summary of CYP2B6 and describes how haplotype information catalogued by PharmVar is utilized by the Pharmacogenomics Knowledgebase (PharmGKB) and the Clinical Pharmacogenetics Implementation Consortium (CPIC).

The association between cigarette smoking and efavirenz plasma concentration using the population pharmacokinetic approach

AIMS

Efavirenz is still widely used as the preferred first-line antiretroviral agent in middle- and low-income countries, including Malaysia. The efavirenz population pharmacokinetic profile among HIV-positive smokers is still unknown. We aimed to assess the association of smoking with efavirenz and the differences in HIV clinical outcomes.

METHODS

A total of 154 stable HIV-positive patients on efavirenz in northern Malaysia were recruited with a sparse sampling for this multicentre prospective cohort study. The association between smoking and efavirenz pharmacokinetic parameters was determined using the nonlinear mixed-effect model. A mixture model of clearance was adopted to describe the metaboliser status because genetic data are unavailable. The effect of smoking on HIV clinical markers (CD4, CD4/CD8 ratio and viral blips) for at least 2 years after the antiretroviral initiation was also investigated.

RESULTS

Our data were best fitted with a 1-compartment mixture model with first-order absorption without lag time. Smoking significantly associated with higher clearance (β = 1.39; 95% confidence interval: 1.07 to 1.91), while weight affected both clearance and volume. From the mixture model, 20% of patients were in the slow clearance group, which mimic the genotype distribution of slow metaboliser. An efavirenz dose reduction is not recommended for smokers ≥60 kg with normal metabolism rate. Smoking significantly associated with slower normalisation of CD4 and CD4/CD8 ratio.

CONCLUSIONS

HIV-positive smokers presented with significantly higher efavirenz clearance and unfavourable clinical outcomes. Close monitoring of adherence and clinical response among smokers is warranted.

Mechanistic Modeling of Maternal Lymphoid and Fetal Plasma Antiretroviral Exposure During the Third Trimester

Pregnancy-induced changes in plasma pharmacokinetics of many antiretrovirals (ARV) are well-established. Current knowledge about the extent of ARV exposure in lymphoid tissues of pregnant women and within the fetal compartment is limited due to their inaccessibility. Subtherapeutic ARV concentrations in HIV reservoirs like lymphoid tissues during pregnancy may constitute a barrier to adequate virological suppression and increase the risk of mother-to-child transmission (MTCT). The present study describes the pharmacokinetics of three ARVs (efavirenz, dolutegravir, and rilpivirine) in lymphoid tissues and fetal plasma during pregnancy using materno-fetal physiologically-based pharmacokinetic models (m-f-PBPK). Lymphatic and fetal compartments were integrated into our previously validated adult PBPK model. Physiological and drug disposition processes were described using ordinary differential equations. For each drug, virtual pregnant women (n = 50 per simulation) received the standard dose during the third trimester. Essential pharmacokinetic parameters, including Cmax, Cmin, and AUC (0-24), were computed from the concentration-time data at steady state for lymph and fetal plasma. Models were qualified by comparison of predictions with published clinical data, the acceptance threshold being an absolute average fold-error (AAFE) within 2.0. AAFE for all model predictions was within 1.08-1.99 for all three drugs. Maternal lymph concentration 24 h after dose exceeded the reported minimum effective concentration (MEC) for efavirenz (11,514 vs. 800 ng/ml) and rilpivirine (118.8 vs. 50 ng/ml), but was substantially lower for dolutegravir (16.96 vs. 300 ng/ml). In addition, predicted maternal lymph-to-plasma AUC ratios vary considerably (6.431-efavirenz, 0.016-dolutegravir, 1.717-rilpivirine). Furthermore, fetal plasma-to-maternal plasma AUC ratios were 0.59 for efavirenz, 0.78 for dolutegravir, and 0.57 for rilpivirine. Compared with rilpivirine (0 h), longer dose forgiveness was observed for dolutegravir in fetal plasma (42 h), and for efavirenz in maternal lymph (12 h). The predicted low lymphoid tissue penetration of dolutegravir appears to be significantly offset by its extended dose forgiveness and adequate fetal compartment exposure. Hence, it is unlikely to be a predictor of maternal virological failure or MTCT risks. Predictions from our m-f-PBPK models align with recommendations of no dose adjustment despite moderate changes in exposure during pregnancy for these drugs. This is an important new application of PBPK modeling to evaluate the adequacy of drug exposure in otherwise inaccessible compartments.

Pharmacogenomics and pharmacokinetics of efavirenz 400 or 600 mg in 184 treatment-naive HIV-infected patients in China

Background: The pharmacogenomics and pharmacokinetics/pharmacodynamics of 400 mg efavirenz have rarely been reported. Materials & methods: A total of 184 treatment-naive HIV-infected patients were randomly assigned (1:1) to receive a lower dose (tenofovir disoproxil 200 mg, efavirenz 400 mg and lamivudine) or a standard dose regimen. Relationships between pharmacogenomics and efavirenz pharmacokinetics/pharmacodynamics were explored at 48 weeks. Results: There was no relationship between pharmacogenomics and adverse reactions of the central nervous system and antiretoviral efficacy. CYP2B6 516G>T, 785A>G, 18492C>T and ABCB1 3435C>T T/C were associated with higher efavirenz plasma levels in the standard but not the lower dose group. No relationship was found between pharmacogenomics and antiretoviral efficacy. Patients who were <60 kg had higher efavirenz concentration compared with those with weight ≥60 kg when using 600 mg efavirenz, this was not observed with 400 mg efavirenz. Conclusion: The effect of pharmacogenomics and body weight on the efavirenz concentration was significant in the 600 mg group but not in the 400 mg group.

Pharmacokinetics of Efavirenz 600 mg Once Daily During Pregnancy and Post Partum in Ghanaian Women Living With HIV

PURPOSE

The updated World Health Organization guidelines recommend efavirenz (EFV) 400 mg as the preferred alternate first-line antiretroviral therapy to dolutegravir, with EFV 600 mg recommended only in special situations. We examined the pharmacokinetic (PK) properties of EFV 600 mg/d during pregnancy and post partum to inform EFV dosing decisions in pregnant women.

METHODS

Ghanaian pregnant women with HIV infection initiating tenofovir disoproxil fumarate 300 mg/lamivudine 300 mg/EFV 600 mg fixed-dose combination tablet once daily were enrolled. Efavirenz concentrations were measured at 4 weeks of antiretroviral therapy initiation during pregnancy and 6 weeks post partum using validated LC-MS/MS assays. Efavirenz PK parameters were calculated using noncompartmental analysis, and within-group parameters between the 2 periods were compared.

FINDINGS

Of 25 enrolled women, 19 completed PK sampling during pregnancy and post partum. The C_max, C_min, AUC_0-24h, and CL/F for EFV during pregnancy were similar to values at 6 weeks post partum. The pregnancy/postpartum geometric mean ratios for EFV C_max, C_min, AUC_0-24, and CL/F were 1.10 (95% CI, 0.93-1.31), 0.88 (95% CI, 0.67-1.17), 0.84 (95% CI, 0.71-0.98), and 1.20 (95% CI, 1.02-1.40), respectively. Viral load suppression (HIV RNA <200 copies/mL) was achieved in 16 of 17 participants (94%) by the time of delivery. There was 1 maternal-to-child transmission.

IMPLICATIONS

We found that the PK parameters of EFV 600 mg once daily during pregnancy were similar to those in the postpartum period. Our findings suggest that EFV dose adjustment during pregnancy is not necessary in our study population.

Drug dosing during pregnancy-opportunities for physiologically based pharmacokinetic models

Drugs can have harmful effects on the embryo or the fetus at any point during pregnancy. Not all the damaging effects of intrauterine exposure to drugs are obvious at birth, some may only manifest later in life. Thus, drugs should be prescribed in pregnancy only if the expected benefit to the mother is thought to be greater than the risk to the fetus. Dosing of drugs during pregnancy is often empirically determined and based upon evidence from studies of non-pregnant subjects, which may lead to suboptimal dosing, particularly during the third trimester. This review collates examples of drugs with known recommendations for dose adjustment during pregnancy, in addition to providing an example of the potential use of PBPK models in dose adjustment recommendation during pregnancy within the context of drug-drug interactions. For many drugs, such as antidepressants and antiretroviral drugs, dose adjustment has been recommended based on pharmacokinetic studies demonstrating a reduction in drug concentrations. However, there is relatively limited (and sometimes inconsistent) information regarding the clinical impact of these pharmacokinetic changes during pregnancy and the effect of subsequent dose adjustments. Examples of using pregnancy PBPK models to predict feto-maternal drug exposures and their applications to facilitate and guide dose assessment throughout gestation are discussed.

Pharmacogenetic interactions between antiretroviral drugs and vaginally administered hormonal contraceptives

OBJECTIVE

In AIDS Clinical Trials Group study A5316, efavirenz lowered plasma concentrations of etonogestrel and ethinyl estradiol, given as a vaginal ring, while atazanavir/ritonavir increased etonogestrel and lowered ethinyl estradiol concentrations. We characterized the pharmacogenetics of these interactions.

METHODS

In A5316, women with HIV enrolled into control (no antiretrovirals), efavirenz [600 mg daily with nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs)], and atazanavir/ritonavir (300/100 mg daily with NRTIs) groups. On day 0, a vaginal ring was inserted, releasing etonogestrel/ethinyl estradiol 120/15 μg/day. Intensive plasma sampling for antiretrovirals was obtained on days 0 and 21, and single samples for etonogestrel and ethinyl estradiol on days 7, 14, and 21. Seventeen genetic polymorphisms were analyzed.

RESULTS

The 72 participants in this analysis included 25, 24 and 23 in the control, efavirenz, and atazanavir/ritonavir groups, respectively. At day 21 in the efavirenz group, CYP2B6 genotype was associated with increased plasma efavirenz exposure (P = 3.2 × 10), decreased plasma concentrations of etonogestrel (P = 1.7 × 10), and decreased ethinyl estradiol (P = 6.7 × 10). Compared to controls, efavirenz reduced median etonogestrel concentrations by at least 93% in CYP2B6 slow metabolizers versus approximately 75% in normal and intermediate metabolizers. Efavirenz reduced median ethinyl estradiol concentrations by 75% in CYP2B6 slow metabolizers versus approximately 41% in normal and intermediate metabolizers.

CONCLUSION

CYP2B6 slow metabolizer genotype worsens the pharmacokinetic interaction of efavirenz with hormonal contraceptives administered by vaginal ring. Efavirenz dose reduction in CYP2B6 slow metabolizers may reduce, but will likely not eliminate, this interaction.

Pharmacokinetics of Efavirenz 400 mg Once Daily Coadministered With Isoniazid and Rifampicin in Human Immunodeficiency Virus-Infected Individuals

Background

The World Health Organization recommends efavirenz 400 mg (EFV400) as first-line antiretroviral therapy, with a disclaimer that no data with anti-tuberculosis (TB) treatment exist. Many people living with human immunodeficiency virus (PLWH) require TB treatment with isoniazid (INH) and rifampicin (RIF), which affect cytochrome P450 and antiretroviral exposure.

Methods

PLWH receiving tenofovir disoproxil fumarate (TDF)/emtricitabine (FTC)/EFV 600 mg with a viral load (VL) <50 copies/mL switched to TDF/FTC/EFV400. Genetic polymorphisms and pharmacokinetic (PK) parameters of EFV400 without (PK1) and with INH/RIF following 4 (PK2) and 12 (PK3) weeks of coadministration were evaluated.

Results

Twenty-six PLWH were enrolled; 22 completed PK2. All maintained VL <50 copies/mL throughout the study. Geometric mean ratio (GMR) PK2/PK1 of EFV400 maximum plasma concentration (Cmax), area under the curve (AUC), and concentration at 24 hours postdose (C24h) were 0.91 (90% confidence interval [CI], .83-.99), 0.91 (90% CI, .79-1.05), and 0.85 (90% CI, .72-.99), respectively. GMRs (90% CI) of PK3/PK2 and PK3/PK1 Cmax, AUC, and C24h were 0.95 (.86-1.05) and 0.92 (.83-1.01), 0.88 (.75-1.03) and 0.84 (.75-.93), and 0.84 (.72-.99) and 0.75 (.62-.92), respectively. Eleven of 22 participants carried polymorphisms in the CYP2B6 gene associated with slow EFV metabolism.

Conclusions

INH/RIF coadministration was associated with limited changes in EFV400 AUC (<25%), and EFV400 concentrations were maintained within ranges of those measured in PLWH in the ENCORE-1 study, irrespective of CYP2B6 genotype. The coadministration of EFV400 with anti-TB treatment can be considered and this is being confirmed in PLWH with TB.

Clinical Trials Registration

NCT02832778.

Impact of Population and Pharmacogenetics Variations on Efavirenz Pharmacokinetics and Immunologic Outcomes During Anti-Tuberculosis Co-Therapy: A Parallel Prospective Cohort Study in Two Sub-Sahara African Populations

Efavirenz-based combination antiretroviral-therapy (cART) is the recommended regimen during tuberculosis (TB) therapy. In a multi-national parallel prospective-cohort study, we investigated the impact of population and pharmacogenetic variations for efavirenz pharmacokinetics, auto-induction, and immunologic outcome during antituberculosis treatment. A total of 921 treatment-naïve HIV patients with (196 Ethiopians and 231 Tanzanians) or without TB co-infection (285 Ethiopians and 209 Tanzanians) were enrolled and treated with efavirenz-based cART. TB-HIV patients started rifampicin-based anti-TB therapy 4 weeks before cART. Efavirenz plasma concentrations were measured on the 4th and 16th weeks of cART. Genotyping for CYP2B6, CYP3A5, ABCB1, UGT2B7, and SLCO1B1 was done. CD4 cells-count was measured at baseline, 12th, 24th, and 48th weeks of cART. Among HIV-only cohort, plasma efavirenz concentration and median CD4 cell count were significantly higher in Tanzanians than Ethiopians, and both CYP2B6 genotype and population-variation were significant predictors of efavirenz plasma concentration. Within-population analyses indicated a pronounced efavirenz autoinduction in Tanzanians as reflected by a significant decrease of plasma efavirenz concentration over time (p = 0.0001), but not in Ethiopians. Among TB-HIV cohort, there were no significant between-population differences in plasma efavirenz concentrations or CD4 cell-recovery, and CYP2B6 genotype but not population-variation was a significant predictor of efavirenz plasma exposure. In Tanzanian patients, short-term anti-TB co-treatment significantly reduced the mean plasma efavirenz concentration in CYP2B6*1/*1 genotype at week-4 (p = 0.005), but not at week-16 of cART. In Ethiopian patients, anti-TB cotreatment increased the mean plasma efavirenz concentration among CYP2B6*6 carriers at week-4 (p = 0.003) and week-16 (p = 0.035) of cART. In general, long-term anti-TB co-treatment increased plasma efavirenz concentration at week 16 of cART in both Ethiopians and Tanzanians being higher in CYP2B6*6/*6 > *1/*6 > *1/*1 genotypes. In TB-HIV patients, baseline body mass index (BMI), viral load, and WHO clinical-stage but not genotype, population-variation, or efavirenz concentration were significant predictors of immunologic outcome at week-48. In summary efavirenz auto-induction, pharmacokinetics, and the immunologic outcome are influenced by population-variation, anti-TB co-medication, and CYP2B6 genotype. CYP2B6 genotype is a significant predictor of efavirenz plasma exposure regardless of population-variation or antituberculosis co-treatment, but population-variation is insignificant during antituberculosis treatment. CYP2B6 genotype, population, and geographic differences need to be considered for efavirenz dosage-optimization.

A Comparison of Plasma Efavirenz and Tenofovir, Dried Blood Spot Tenofovir-Diphosphate, and Self-Reported Adherence to Predict Virologic Suppression Among South African Women

BACKGROUND

Tenofovir-diphosphate (TFV-DP) in dried blood spots (DBS) is an objective long-term adherence measure, but data are limited on its ability to predict virologic suppression (VS) in people on antiretroviral (ARV) treatment. There are also no data comparing DBS TFV-DP with plasma ARV concentrations as predictors of VS.

METHODS

Women who were on a first-line regimen of tenofovir, emtricitabine, and efavirenz (EFV) were enrolled in a cross-sectional study. Plasma EFV and tenofovir (TFV), DBS TFV-DP assays, and 30-day self-reported adherence were evaluated as predictors of VS (<50 copies/mL) with the area under the curve of receiver operating characteristics and logistic regression.

RESULTS

We enrolled 137 women; mean age of 33 years; median 4 years on antiretroviral therapy; 88 (64%) had VS. In receiver operating characteristics analyses: DBS TFV-DP [0.926 (95% CI: 0.876 to 0.976)] had a higher area under the curve than plasma TFV [0.864 (0.797 to 0.932); P = 0.006], whereas plasma EFV [0.903 (0.839-0.967)] was not significantly different from DBS TFV-DP (P = 0.138) or plasma TFV (P = 0.140); all ARV assays performed better than self-report. The association of TFV-DP in DBS with VS strengthened with increasing concentrations [reference <350 fmol/punch: 350-699 fmol/punch aOR 37 (8-178); 700-1249 fmol/punch aOR 47 (13-175); ≥1250 fmol/punch aOR 175 (20-1539)]. "White coat adherence" (defined as DBS TFV-DP <350 fmol/punch with detectable plasma TFV) was only detected in 4 women.

CONCLUSIONS

Plasma EFV, TFV, and DBS TFV-DP were all strong predictors of VS. EFV or TFV assays have potential for development as point-of-care assays for use as objective adherence measures in resource-limited settings.

Rational Design of Doravirine: From Bench to Patients

Since the approval of nevirapine, the first HIV-1 non-nucleoside reverse transcriptase inhibitor (NNRTI) in 1996, NNRTIs have helped play a critical role in maintaining viral suppression in people living with HIV. The many positive attributes of the class, including potency and long plasma half-life, make them attractive drug discovery targets. Given the availability of multiple once-daily integrase-based treatments for HIV-1 infection, the challenge to develop a new antiretroviral agent that addresses the needs of today's patients is formidable. However, with the increased availability of antiretrovirals for treatment and new pre-exposure prophylaxis guidelines, which should globally expand the use of antiretrovirals in prevention, it will be increasingly important to have access to multiple regimens with options from different classes that are well tolerated and convenient to ensure a sustained impact on the global epidemic. Many attempts to improve upon the NNRTI class have failed to deliver a desirable clinical profile consistent with the current landscape of treatment options. Doravirine is the only NNRTI to successfully advance through phase 3 clinical development and approval in recent years. Learning from the liabilities of approved NNRTIs, as well as past development failures, facilitated a rational approach to the discovery of doravirine by focusing on addressing the known safety/tolerability issues of commonly prescribed NNRTIs, such as central nervous system toxicity with efavirenz and potential cardiotoxicity due to off-target effects on cardiac ion channels with rilpivirine, using structural biology and characterization of resistance in vitro to address resistance liabilities and concentrating on the metabolic profile to limit the potential for drug-drug interactions. These preclinical efforts were critical to the design and selection of doravirine as a novel NNRTI that possessed the desired next-generation profile with the ultimate proof that these attributes translate to patients derived from clinical trials.

Safety implications of combined antiretroviral and anti-tuberculosis drugs

Introduction: Antiretroviral and anti-tuberculosis (TB) drugs are often co-administered in people living with HIV (PLWH). Early initiation of antiretroviral therapy (ART) during TB treatment improves survival in patients with advanced HIV disease. However, safety concerns related to clinically significant changes in drug exposure resulting from drug-drug interactions, development of overlapping toxicities and specific challenges related to co-administration during pregnancy represent barriers to successful combined treatment for HIV and TB.Areas covered: Pharmacokinetic interactions of different classes of ART when combined with anti-TB drugs used for sensitive-, drug-resistant (DR) and latent TB are discussed. Overlapping drug toxicities, implications of immune reconstitution inflammatory syndrome (IRIS), safety in pregnancy and research gaps are also explored.Expert opinion: New antiretroviral and anti-tuberculosis drugs have been recently introduced and international guidelines updated. A number of effective molecules and clinical data are now available to build treatment regimens for PLWH with latent or active TB. Adopting a systematic approach that also takes into account the need for individualized variations based on the available evidence is the key to successfully integrate ART and TB treatment and improve treatment outcomes.

A Review of Clinical Pharmacokinetic and Pharmacodynamic Profiles of Select Antiretrovirals: Focus on Differences among Chinese Patients

OBJECTIVE

To identify the pharmacokinetic differences of antiretroviral drugs between HIV-infected Chinese patients and patients of other race/ethnicities.

STUDY DESIGN

Results from prospective, open-label pharmacokinetic studies among Chinese and historical data from other race/ethnicities.

PATIENTS

Pharmacokinetics of six commonly used antiretroviral drugs, including zidovudine, lamivudine, tenofovir disoproxil fumarate, nevirapine, efavirenz and lopinavir/ritonavir, was evaluated in HIV-infected Chinese patients and compared with historical data from other race/ethnicities.

ANALYSIS

Pharmacokinetic analyses were performed at the steady state among HIV-infected Chinese patients. Safety data were collected during the follow-up. The pharmacokinetic parameters including maximal concentrations (Cmax), area-under-curve (AUC) and clearance (Cl/F) from the Chinese patients were compared to the historic data from other race/ethnicities.

RESULTS

Current evidence, though limited, suggested that these antiretroviral agents were generally safe and effective among HIV-infected Chinese patients. However, compared with other racial groups, Chinese patients exhibited higher C_max , AUC and lower Cl/F for most of the agents, and the incidences of adverse reactions, for example, liver toxicity, rash, and bone health, were more frequent.

CONCLUSIONS

These pharmacokinetic differences suggest that lower dosages for commonly prescribed antiretroviral drugs in China might be appropriate to reduce drug-related adverse reactions, while maintain the antiviral efficacy.

Impact of Integrase Inhibition Compared With Nonnucleoside Inhibition on HIV Reservoirs in Lymphoid Tissues

BACKGROUND

HIV is produced in lymphoid tissues (LT) and stored on the follicular dendritic cell network in LT. When antiretroviral therapy is started, plasma viremia decays in 2 phases; the first within days of starting therapy and the second over weeks. Raltegravir (RAL), an integrase inhibitor, has been associated with only a single rapid phase of decay, and we speculated this may be due to higher intracellular concentration (IC) of RAL in LT. We have previously measured suboptimal ICs of antiretroviral therapy agents in LT, which were associated with slower decay of both vRNA+ cells and the follicular dendritic cell network pool.

SETTING

Outpatient clinic at the Joint Clinical Research Center in Kampala, Uganda.

METHODS

We compared the rate of decay in LT in people starting RAL with those starting efavirenz (EFV).

RESULTS

There was no difference in the rate of virus decay in LT. The ratio of the ICs of RAL and EFV in lymph node to the concentration of drug that inhibits 95% of virus in blood was 1 log lower in lymph node for EFV and >3 logs lower for RAL.

CONCLUSION

These data further highlight the challenges of drug delivery to LT in HIV infection and demonstrate that RAL is not superior to EFV as judged by direct measurements of the source of virus in LT.

Role of efavirenz plasma concentrations on long-term HIV suppression and immune restoration in HIV-infected children

Background

To access the long term relationship between efavirenz plasma concentrations and evolution of HIV RNA loads and CD4 cell counts in children.

Methods

Retrospective analysis of data from HIV-infected children on first line efavirenz-containing regimen. A population pharmacokinetic-pharmacodynamic (PK-PD) model was developed to describe the evolution of HIV RNA load and CD4 cell count (efficacy outcomes) in relation to efavirenz plasma concentration. Individual CYP2B6 516 G>T genotype data were not available for this analysis. A score (IS_EFV) quantifying the effect of efavirenz concentrations on the long-term HIV replication was calculated from efavirenz concentrations and PD parameters and, a value of IS_EFV below which HIV replication is likely not suppressed was determined. Cox proportional hazards regression models were used to assess the association of the risk of viral replication with IS_EFV, and with efavirenz mid-dose concentration(C₁₂).

Results

At treatment initiation, median (interquartile range, IQR) age was 8 years (5 to 10), body weight 17 kg (14 to 23), HIV RNA load 5.1 log₁₀ copies/mL (4.6 to 5.4), and CD4 cell count 71 cells/mm³. A model of PK-PD viral dynamics assuming that efavirenz decreases the rate of infected host cells adequately described the relationship of interest. After adjusting for age, baseline HIV RNA load and CD4 cell counts an IS_EFV <85% was significantly associated with a higher risk of viral replication (p-value <0.001) while no significant association was observed with C₁₂ <1.0 mg/L.

Conclusion

The IS_EFV score was a good predictor of viral replication in children on efavirenz-based treatment.

The Utility of Efavirenz-based Prophylaxis Against HIV Infection. A Systems Pharmacological Analysis

Pre-exposure prophylaxis (PrEP) is considered one of the five “pillars” by UNAIDS to reduce HIV transmission. Moreover, it is a tool for female self-protection against HIV, making it highly relevant to sub-Saharan regions, where women have the highest infection burden. To date, Truvada is the only medication for PrEP. However, the cost of Truvada limits its uptake in resource-constrained countries. Similarly, several currently investigated, patent-protected compounds may be unaffordable in these regions. We set out to explore the potential of the patent-expired antiviral efavirenz (EFV) as a cost-efficient PrEP alternative. A population pharmacokinetic model utilizing data from the ENCORE1 study was developed. The model was refined for metabolic autoinduction. We then explored EFV cellular uptake mechanisms, finding that it is largely determined by plasma protein binding. Next, we predicted the prophylactic efficacy of various EFV dosing schemes after exposure to HIV using a stochastic simulation framework. We predicted that plasma concentrations of 11, 36, 1287 and 1486ng/mL prevent 90% sexual transmissions with wild type and Y181C, K103N and G190S mutants, respectively. Trough concentrations achieved after 600 mg once daily dosing (median: 2017 ng/mL, 95% CI:445–9830) and after reduced dose (400 mg) efavirenz (median: 1349ng/mL, 95% CI: 297–6553) provided complete protection against wild-type virus and the Y181C mutant, and median trough concentrations provided about 90% protection against the K103N and G190S mutants. As reduced dose EFV has a lower toxicity profile, we predicted the reduction in HIV infection when 400 mg EFV-PrEP was poorly adhered to, when it was taken “on demand” and as post-exposure prophylaxis (PEP). Once daily EFV-PrEP provided 99% protection against wild-type virus, if ≥50% of doses were taken. PrEP “on demand” provided complete protection against wild-type virus and prevented ≥81% infections in the mutants. PEP could prevent >98% infection with susceptible virus when initiated within 24 h after virus exposure and continued for at least 9 days. We predict that 400 mg oral EFV may provide superior protection against wild-type HIV. However, further studies are warranted to evaluate EFV as a cost-efficient alternative to Truvada. Predicted prophylactic concentrations may guide release kinetics of EFV long-acting formulations for clinical trial design.

Efavirenz pharmacokinetics during pregnancy and infant washout

BACKGROUND

Limited data exist on efavirenz pharmacokinetics in HIV-positive pregnant women and neonatal washout.

METHODS

HIV-infected pregnant women receiving 600 mg efavirenz once daily had intensive steady-state 24-h pharmacokinetics profiles during the second trimester (2T), third trimester (3T) and 6-12 weeks postpartum (PP). Maternal and umbilical cord blood samples were drawn at delivery and neonatal washout pharmacokinetics were determined. Therapeutic targets were the estimated 10th percentile efavirenz area under the concentration-time curve (AUC) in non-pregnant historical controls (40.0 μg•h/ml) and a trough concentration (C24 h) of 1 μg/ml. Data were prospectively collected within two trials: IMPAACT P1026s (United States) and PANNA (Europe).

RESULTS

Among 42 women studied, 15, 42 and 40 had efavirenz pharmacokinetic data available in 2T, 3T and PP, respectively. Median (range) 3T age 33 (20.7-43.5) years, weight 74 (50-132) kg and gestational age 33.4 (28.4-37.9 weeks). Efavirenz AUC during the 3T (60 μg•h/ml) was similar to that reported in non-pregnant adults (58 μg•h/ml). Exposure in the 2T was lower, but within the 0.80-1.25 range. C24 concentrations during pregnancy were lower compared to historical controls on 600 mg efavirenz, however, they were similar to the C24 concentrations after equally potent dose of 400 mg efavirenz. Cord blood/maternal plasma concentration ratio (range) was 0.67 (0.36-0.95). Among 23 infants with washout data available, median (interquartile range) elimination half-life was 65.6 h (40.6-129). HIV RNA viral loads at delivery were <400 and <50 copies/ml for 96.7% and 86.7% of women, respectively. In 3T and PP, respectively, 8/41 (19%) and 6/40 (15%) had AUC below target; 7/41 (17%) and 3/39 (8%) had C24 below target.

CONCLUSIONS

Efavirenz exposure was similar during pregnancy compared with PP, C24 was in line with C24 after 400 mg equipotent efavirenz dosing. Efavirenz readily crossed the placenta and infant elimination half-life was over twice that of maternal participants. Clincaltrials.gov identifiers: NCT00825929 and NCT00042289.

A Mechanism-Based Population Pharmacokinetic Analysis Assessing the Feasibility of Efavirenz Dose Reduction to 400 mg in Pregnant Women

BACKGROUND

Reducing the dose of efavirenz can improve safety, reduce costs, and increase access for patients with HIV infection. According to the World Health Organization, a similar dosing strategy for all patient populations is desirable for universal roll-out; however, it remains unknown whether the 400 mg daily dose is adequate during pregnancy.

METHODS

We developed a mechanistic population pharmacokinetic model using pooled data from women included in seven studies (1968 samples, 774 collected during pregnancy). Total and free efavirenz exposure (AUC24 and C12) were predicted for 400 (reduced) and 600 mg (standard) doses in both pregnant and non-pregnant women.

RESULTS

Using a 400 mg dose, the median efavirenz total AUC24 and C12 during the third trimester of pregnancy were 91 and 87% of values among non-pregnant women, respectively. Furthermore, the median free efavirenz C12 and AUC24 were predicted to increase during pregnancy by 11 and 15%, respectively.

CONCLUSIONS

It was predicted that reduced-dose efavirenz provides adequate exposure during pregnancy. These findings warrant prospective confirmation.

Evaluation of universal versus genotype-guided efavirenz dose reduction in pregnant women using population pharmacokinetic modelling

Objectives

Lack of data on the pharmacokinetics of efavirenz in pregnant women at the 400 mg reduced dose currently prevents universal roll-out. Population pharmacokinetic modelling was used to explore pharmacokinetic endpoints at 200, 400 and 600 mg daily doses in pregnant women stratified by CYP2B6 metabolic status.

Methods

The analysis was based on 252 plasma efavirenz concentrations from 77 pregnant women (77 sparse, 175 intensive) who received antiretroviral regimens containing 600 mg of efavirenz. The model was developed using NONMEM®. The effect of genetics was investigated and concentration-time courses at steady-state were simulated for individuals (n = 1000 each) classified as CYP2B6 slow, intermediate and fast metabolizers at 200, 400 and 600 mg daily doses.

Results

At a 400 mg reduced dose, predicted mean (90% CI) mid-dose efavirenz concentration (C12) was 2.24 μg/mL (0.89-4.18) in pregnant women classified as slow metabolizers, compared with 0.87 μg/mL (0.34-1.64) in intermediate metabolizers and 0.78 μg/mL (0.30-1.47) in fast metabolizers. C12 was below the 0.47 μg/mL threshold determined within the ENCORE 1 trial in 10% at 400 mg, 4.6% at 600 mg and 3.4% with genotype-guided dosing. The 4.0 μg/mL toxicity threshold was exceeded in 4.6% at 400 mg, 13.5% at 600 mg and 5.2% with genotype-guided dosing.

Conclusions

These data provide context for the ongoing debate about reduction in efavirenz dose to 400 mg during pregnancy and should be interpreted alongside the lower toxicity expected with the lower dose. Additional research is required to investigate genotype-guided dose reduction in pregnant women.

Effectiveness of half-a-tablet efavirenz plus 2 nucleos(t)ide reverse-transcriptase inhibitors as maintenance therapy with the guidance of therapeutic drug monitoring among virologically suppressed HIV-positive patients: A prospective study

BACKGROUND

Optimal efavirenz (EFV) dose that minimizes adverse effects while maintaining efficacy has yet to be elucidated. With a therapeutic drug monitoring (TDM)-guided strategy, we assessed the effectiveness of half-a-tablet EFV plus 2 nucleos(t)ide reverse-transcriptase inhibitors (NRTIs) in HIV-infected Taiwanese who had achieved viral suppression with full-dose (600 mg) EFV.

METHODS

HIV-infected adults receiving EFV-containing regimens who had plasma mid-dose EFV concentration (C12) ≥2.0 mg/L and had plasma HIV RNA load (PVL) <200 copies/mL were enrolled in this single-arm, open-label study by reducing EFV to half-a-tablet daily. The primary endpoint was PVL <50 copies/ml in an intention-to-treat (ITT) population at week 48. The secondary endpoints were the plasma EFV C12, the proportion of patients with plasma EFV C12 <1.0 mg/L, PVL <50 copies/ml at week 96 and week 144.

RESULTS

Between April 2013 and September 2016, 203 patients (93.6% male; median age, 39.0 years) were enrolled. The median EFV C12 before switch was 2.80 mg/L (interquartile range (IQR), 2.41-3.73), which decreased to 1.59 mg/L (IQR, 1.23-2.03) after switch with a reduction of 47.4% (IQR, 38.3-55.5%). In ITT analysis, 93.6%, 92.3% and 87.3% of the patients achieved PVL <50 copies/ml at weeks 48, 96 and 144, respectively. More than 70% of the patients reported alleviation of EFV-associated adverse effects following the switch.

CONCLUSION

Under the guidance of TDM, switch to half-a-tablet EFV plus 2 NRTIs is effective in maintaining viral suppression in HIV-infected Taiwanese with EFV C12 ≥ 2.0 mg/L.

Pharmacokinetics of efavirenz in patients on antituberculosis treatment in high human immunodeficiency virus and tuberculosis burden countries: A systematic review

AIMS

Efavirenz (EFV) and rifampicin-isoniazid (RH) are cornerstone drugs in human immunodeficiency virus (HIV)-tuberculosis (TB) coinfection treatment but with complex drug interactions, efficacy and safety challenges. We reviewed recent data on EFV and RH interaction in TB/HIV high-burden countries.

METHODS

We conducted a systematic review of studies conducted in the high TB/HIV-burden countries between 1990 and 2016 on EFV pharmacokinetics during RH coadministration in coinfected patients. Two reviewers conducted article screening and data collection.

RESULTS

Of 119 records retrieved, 22 were included (two conducted in children), reporting either EFV mid-dose or pre-dose concentrations. In 19 studies, median or mean concentrations of RH range between 1000 and 4000 ng ml^-1 , the so-called therapeutic range. The proportion of patients with subtherapeutic concentration of RH ranged between 3.1 and 72.2%, in 12 studies including one conducted in children. The proportion of patients with supratherapeutic concentration ranged from 19.6 to 48.0% in six adult studies and one child study. Five of eight studies reported virological suppression >80%. The association between any grade hepatic and central nervous system adverse effects with EFV/RH interaction was demonstrated in two and three studies, respectively. The frequency of the CYP2B6 516G > T polymorphism ranged from 10 to 28% and was associated with higher plasma EFV concentrations, irrespective of ethnicity.

CONCLUSIONS

Anti-TB drug coadministration minimally affect the EFV exposure, efficacy and safety among TB-HIV coinfected African and Asian patients. This supports the current 600 mg EFV dosing when coadministered with anti-TB drugs.

Prospective plasma efavirenz concentration assessment in Chinese HIV-infected adults enrolled in a large multicentre study

OBJECTIVES

Few studies have explored the optimal dosing for efavirenz in individuals from China. We investigated plasma efavirenz concentrations and their association with efficacy and tolerance of efavirenz 600 mg daily in Chinese HIV-infected adults.

METHODS

An analysis was performed using plasma samples from 455 patients enrolled in a prospective multicentre trial in China. A total of 1198 plasma samples collected at weeks 4, 24 and 48 following antiretroviral therapy initiation were analysed. The mid-dose interval efavirenz concentrations (C12 ) were determined using high-performance liquid chromatography.

RESULTS

The median efavirenz concentration (interquartile range) steadily increased over time from 3.02 (2.28-4.23) to 3.71 (2.91-4.91) mg/L from week 4 to 48 (P < 0.001). The proportion of patients with C12 > 4.0 mg/L also rose from 28.0% to 34.2% and 43.8%, measured at 4, 24 and 48 weeks, respectively (P < 0.001). Five patients had efavirenz concentrations < 1.0 mg/L at week 4, 24 or 48. In the multivariable regression analysis, lower body weight and non-Han ethnicities were associated with higher efavirenz concentrations over time. At each time-point, patients with a body weight < 60 kg had significantly higher efavirenz C12 compared with those with body weight ≥ 60 kg (P < 0.05).

CONCLUSIONS

Efavirenz concentrations increased steadily over 48 weeks, and a substantial proportion of participants had efavirenz C12 above the upper limit of the proposed therapeutic window, especially those with low body weight (< 60 kg). Based upon these findings, a dosage reduction of efavirenz to 400 mg daily may warrant consideration in this population, especially for those with lower body weight.

Physiologically-based pharmacokinetic modelling of infant exposure to efavirenz through breastfeeding

Background: Very little is known about the level of infant exposure to many drugs commonly used during breastfeeding. The aim of this study was to develop a physiologically-based pharmacokinetic (PBPK) model for predicting infant exposure to maternal efavirenz through breastmilk. Methods: A breastfeeding PBPK model combining whole-body maternal and infant sub-models was constructed from drug-specific and system parameters affecting drug disposition using mathematical descriptions. The model was validated against published data on the pharmacokinetics of efavirenz in nursing mother-infant pairs. Further simulations were conducted to assess exposure in the context of the 400 mg reduced dose of efavirenz as well as best- and worse-case scenarios. Results: The model adequately described efavirenz pharmacokinetics, with over 80% of observed data points (203 matched breast milk and plasma pairs) within the predictive interval. All parameters were within 2-fold difference of clinical data. Median (range) predicted versus observed breast milk AUC0-24, Cmax and Cmin at the standard 600 mg dose were 75.0 (18.5-324) versus 68.5 (26.3-257) µg.hr/mL, 4.56 (1.17-16.0) versus 5.39 (1.43-18.4) µg/mL, and 2.11 (0.38-12.3) versus 1.68 (0.316-9.57) µg/mL, respectively. Predicted plasma AUC0-24, Cmax and Cmin at 400 mg reduced dose were similar to clinical data from non-breastfeeding adults. Model-predicted infant plasma concentrations were similar to clinical data, 0.15 (0.026–0.78) μg/mL at the 400 mg maternal dose in pooled analysis, approximately 25% lower than simulated exposure at 600 mg. The maximum exposure index was observed in the youngest infants, 5.9% (2.2-20) at 400 mg and 8.7% (3.2-29) at 600 mg. Thirteen and 36% of 10 days-1 month old infants were predicted to have exposure index above the 10% recommended threshold at 400 mg and 600 mg maternal dose, respectively. Conclusions: This application of PBPK modelling opens up opportunities for expanding our understanding of infant exposure to maternal drugs through breastfeeding.

Application of Physiologically Based Pharmacokinetic (PBPK) Modeling Within a Bayesian Framework to Identify Poor Metabolizers of Efavirenz (PM), Using a Test Dose of Efavirenz

Poor metabolisers of CYP2B6 (PM) require a lower dose of efavirenz because of serious adverse reactions resulting from the higher plasma concentrations associated with a standard dose. Treatment discontinuation is a common consequence in patients experiencing these adverse reactions. Such patients benefit from appropriate dose reduction, where efficacy can be achieved without the serious adverse reactions. PMs are usually identified by genotyping. However, in countries with limited resources genotyping is unaffordable. Alternative cost-effective methods of identifying a PM will be highly beneficial. This study was designed to determine whether a plasma concentration corresponding to a 600 mg test dose of efavirenz can be used to identify a PM. A physiologically based pharmacokinetic (PBPK) model was used to simulate the concentration-time profiles of a 600 mg dose of efavirenz in extensive metabolizers (EM), intermediate metabolizers (IM), and PM of CYP2B6. Simulated concentration-time data were used in a Bayesian framework to determine the probability of identifying a PM, based on plasma concentrations of efavirenz at a specific collection time. Results indicated that there was a high likelihood of differentiating a PM from other phenotypes by using a 24 h plasma concentration. The probability of correctly identifying a PM phenotype was 0.82 (true positive), while the probability of not identifying any other phenotype as a PM (false positive) was 0.87. A plasma concentration >1,000 ng/mL at 24 h post-dose is likely to be from a PM. Further verification of these findings using clinical studies is recommended.

Development of Guanfacine Extended-Release Dosing Strategies in Children and Adolescents with ADHD Using a Physiologically Based Pharmacokinetic Model to Predict Drug-Drug Interactions with Moderate CYP3A4 Inhibitors or Inducers

BACKGROUND

Guanfacine extended-release (GXR) is an orally administered, non-stimulant treatment for children and adolescents with attention-deficit/hyperactivity disorder (ADHD) and is primarily metabolized by the 3A4 isozyme of cytochrome P450 (CYP3A4). The results of clinical pharmacokinetic (PK) studies indicate that guanfacine is sensitive to drug-drug interactions (DDIs) perpetrated by strong inhibitors and inducers of CYP3A4.

OBJECTIVE

The aim was to provide guidance on the possible requirement for GXR dose adjustment in children and adolescents with ADHD by predicting DDIs following co-administration with moderate CYP3A4 inhibitors and inducers.

METHODS

A physiologically based PK model for GXR orally administered to healthy adults was developed based on physicochemical, in vitro and clinical PK data. The model was validated using clinical PK data for co-administration of GXR with ketoconazole (strong CYP3A4 inhibitor) or rifampicin (strong CYP3A4 inducer).

RESULTS

Model predictions indicated that co-administration of GXR with the moderate CYP3A4 inhibitors erythromycin 500 mg three times a day or fluconazole 200 mg daily (q.d.) increased the guanfacine area under the plasma concentration-time curve (AUC) by 2.31-fold or 1.98-fold, respectively, compared with GXR monotherapy. The moderate CYP3A4 inducer efavirenz 400 mg or 600 mg q.d. was predicted to reduce guanfacine AUC to 58 or 33% of its value for GXR monotherapy, respectively.

CONCLUSION

Without the requirement for additional clinical studies, the following GXR dose recommendations were developed and approved for US labeling for use in children and adolescents with ADHD: (1) decrease GXR to 50% of the usual target dose when it is co-administered with strong or moderate CYP3A4 inhibitors; (2) consider titrating GXR up to double the usual target dose over 1-2 weeks when it is co-administered with strong or moderate CYP3A4 inducers.

NeuroAIDS in children

The human immunodeficiency virus-1 (HIV-1) enters the central nervous system compartment within the first few weeks of systemic HIV infection and may cause a spectrum of neurologic complications. Without combination antiretroviral therapy (cART), 50-90% of all HIV-infected infants and children develop some form of neuroAIDS. Of the estimated 2.3 million children less than 15 years of age who were living in sub-Saharan Africa at the end of 2014, only 30% were receiving cART, suggesting that there is a large burden of neuroAIDS among HIV-infected children in sub-Saharan Africa. There is complex interplay between the disease process itself, the child's immune reaction to the disease, the secondary complications, the side-effects of antiretroviral drugs, and inadequate antiretroviral drug uptake into the central nervous system. In addition there is the layering effect from the multiple socioeconomic challenges for children living in low- and middle-income countries. Adolescents may manifest with a range of neurocognitive sequelae from mild neurocognitive disorder through to severe neurocognitive impairment. Neuroimaging studies on white-matter tracts have identified dysfunction, especially in the frontostriatal networks needed for executive function. Psychiatric symptoms of depression, attention deficit hyperactivity disorder, and behavioral problems are also commonly reported in this age group. Antiretroviral drugs may cause treatment-limiting neurologic and neuropsychiatric adverse reactions. The following chapter addresses the neurologic complications known to be, and suspected of being, associated with HIV infection in children and adolescents.

Efavirenz Therapeutic Range in HIV-1 Treatment-Naive Participants

BACKGROUND

Efavirenz is currently suggested as an alternative to recommended antiretroviral (ARV) regimens by the Department of Health and Human Services for the treatment of HIV-1 in ARV-naive patients. A mid-dosing interval therapeutic range between 1000 and 4000 ng/mL for efavirenz has been proposed in the literature, with patients more likely to experience virologic failure below this range and adverse effects above. The current study reports an analysis of virologic outcome between those above, below, or within the reported efavirenz therapeutic range (1000-4000 ng/mL) and within subgroups.

METHODS

This analysis examined efavirenz plasma concentrations obtained from participants enrolled in AIDS Clinical Trials Group Study A5202. This investigation divided subjects into those who experienced virologic failure and those who did not. These subjects were further separated to investigate those who had "high," "within," or "low" plasma concentrations, based on the therapeutic range. The association between virologic failure and plasma concentration was statistically examined in addition to the variables: race/ethnicity, sex, assigned nucleos(t)ide reverse transcriptase inhibitor backbone, age at study entry, history of intravenous drug use, weight, and screening HIV-1 RNA stratification level.

RESULTS

In univariate analyses, a statistically significant difference was found when comparing the efavirenz concentration groups, (22 failures among the "low" concentration group [19%], 65 failures among the "within" concentration group [12%], and 11 failures among the "high" concentration group [9%]) when evaluating virologic failure as an outcome (P = 0.04). In addition, the proportion of participants with virologic failure differed across race/ethnicity groups (P = 0.03) with black non-Hispanic participants observed to have the highest rate (17%). Efavirenz concentration group, race/ethnicity, age, weight, and the interaction between efavirenz concentration group and weight were found to be significantly associated with virologic failure in multivariable logistic regression analysis.

CONCLUSIONS

The proposed efavirenz therapeutic range, combined with the impact of a patient's weight, is associated with virologic failure in HIV-infected ARV-naive individuals in the United States. Additional analysis is recommended to determine the most appropriate concentration value that defines the lower limit of the efavirenz therapeutic range.

Prediction of plasma efavirenz concentrations among HIV-positive patients taking efavirenz-containing combination antiretroviral therapy

We investigated the predictors of plasma mid-dose concentrations (C12) of efavirenz by enrolling 456 HIV-positive patients who had received 2 nucleos(t)ide reverse-transcriptase inhibitors plus efavirenz (600 mg daily) for 2 weeks or longer and had their CYP2B6 516G>T polymorphism and efavirenz C12 determined. The median efavirenz C12 was 2.41 mg/L (IQR, 1.93–3.14). In analysis of covariance models, patients with CYP2B6 516GT and TT genotypes compared to those with GG genotype had higher efavirenz C12 (for GT genotype, an increase by 0.976 mg/L [95%CI, 0.765–1.188], and TT genotype, 4.871 mg/L [95%CI, 4.126–5.616]), while per 10-kg increment in weight decreased C12 by 0.199 mg/L (95%CI, 0.111–0.287). Models incorporating CYP2B6 516G>T polymorphism and weight had moderate predictive values in predicting efavirenz C12 ≥ 2 mg/L (ROC area under curve = 0.706 [95%CI, 0.656–0.756]). In the absence of CYP2B6 516G>T polymorphism, weight ≤58 kg provided better predictabilities for efavirenz C12 ≥ 2 mg/L (probability, 77.1% [95%CI, 69.0–83.5%] for weight = 50 kg and 70.6% [95%CI, 64.1–76.4%] for weight = 58 kg).

Genetic Polymorphisms Affecting the Pharmacokinetics of Antiretroviral Drugs

BACKGROUND

Antiretroviral treatment is highly effective in enhancing HIV-positive patients' survival and quality of life. Despite an increased tolerability in recent years, a substantial amount of patients experience side effects. Antiretrovirals' efficacy and tolerability have been associated with plasma concentrations and single nucleotide polymorphisms in selected genes involved in drug disposition.

OBJECTIVE

Our aim was to review the current knowledge in genetic polymorphisms affecting plasma, intracellular or compartmental concentrations of antiretrovirals.

METHODS

A search of the PubMed database was conducted to identify relevant articles, using the following terms: 'pharmacogenetics' or 'pharmacogenomics' or 'single nucleotide polymorphisms' or 'genetic/allelic variants' and 'pharmacokinetics' or 'concentrations' and 'HIV' or 'antiretroviral'. Abstracts from the main HIV conferences during 2015 and 2016 were also searched using the same keywords. Abstracts were manually checked and, if relevant, full papers were obtained. Only articles published in English were selected.

RESULTS

Several genetic polymorphisms in genes coding enzymes involved in drug metabolism (cytochrome P450 isoenzymes and uridine diphosphate glucuronosyltransferases) and transport (P-glycoprotein, anionic and cationic transporters, other transporters), as well as nuclear receptors (pregnane X receptor and the constitutive androstane receptor), have been associated with concentrations of antiretrovirals. The extent of such influence, the conflicting data, and the potential clinical relevance are discussed in the main section of this article.

CONCLUSION

Genetic polymorphisms may affect antiretroviral disposition, as well as both efficacy and toxicity. Despite a large amount of data, such precious knowledge has seldom been applied in patients. Studies on the clinical relevance and cost effectiveness of tailoring antiretroviral regimens to patients' genetic assets are lacking, but their importance may grow with the increasing age and complexity of persons living with HIV/AIDS.

Antiretroviral dose optimization: the future of efavirenz 400 mg dosing

PURPOSE OF REVIEW

Antiretroviral (ARV) therapy costs in low-income and middle-income countries are major concerns, and lower doses of first-line treatment components, when possible, would save millions of dollars, which could be used to treat more people living with HIV.

RECENT FINDINGS

The Encore-1 study, followed by a detailed pharmacokinetic analysis of efavirenz 400 versus 600 mg once daily, produced enough information for the most recent ARV treatment WHO guidelines to include efavirenz 400 mg among agents used for first-line treatment. However, data on efavirenz 400 mg plasma concentrations during pregnancy and when coadministered with rifampicin-containing antituberculosis (TB) treatment are not yet available as formal pharmacokinetic studies under these circumstances are ongoing.

SUMMARY

Although efavirenz at a daily dose of 400 mg once daily in combination with tenofovir disoproxil fumarate and emtricitabine has shown noninferiority to the approved 600 mg once-daily dose, large global uptake has been delayed by the lack of data on drug exposure during pregnancy and anti-TB treatment. Knowledge on efavirenz 400 mg exposure in these scenarios will arise in mid-late 2017.

Comprehensive Pharmacokinetic, Pharmacodynamic and Pharmacogenetic Evaluation of Once-Daily Efavirenz 400 and 600 mg in Treatment-Naïve HIV-Infected Patients at 96 Weeks: Results of the ENCORE1 Study

Background

ENCORE1 demonstrated non-inferiority of daily efavirenz 400 mg (EFV400) versus 600 mg (EFV600) to 96 weeks in treatment-naïve, HIV-infected adults but concerns regarding lower EFV400 concentrations remained. Therefore, relationships between EFV pharmacokinetics (PK) and key genetic polymorphisms with 96-week efficacy and safety were investigated.

Methods

Relationships between EFV PK parameters and single nucleotide polymorphisms (SNP; CYP2B6,CYP2A6, CYP3A4, NR1I3, NR1I2, ABCB1) with plasma HIV-RNA (pVL) <200 copies/mL and EFV discontinuation and adverse events at 96 weeks were explored. Receiver operating characteristic curve analysis evaluated the predictability of mid-dose interval (C₁₂) cutoffs and 96-week pVL.

Results

A total of 606 patients (32 % female; 37 % African, 33 % Asian; n = 311 EFV400, n = 295 EFV600) were included. EFV PK parameters, including C₁₂, were not associated with pVL <200 copies/mL at 96 weeks (odds ratio [OR] 5.25, 95 % confidence interval [CI] 0.41–67.90, p = 0.204). Lower risk of CNS-related adverse events was associated with CYP2B6 983TC/CC (OR 0.35, 95 % CI 0.15–0.81, p = 0.015) and higher risk was associated with CYP2B6 15582CT/TT and ABCB1 3435TT (OR 1.46, 95 % CI 1.02–2.09, p = 0.040; OR 2.31, 95 % CI 1.33–4.02, p = 0.003, respectively). Discontinuation due to adverse events (clinician decision) was independently associated with dose (OR 2.54, 95 % CI 1.19–5.43, p = 0.016). C₁₂ between 0.47 and 0.76 mg/L provided sensitivity/specificity >90 % (100 %/92.3 to 98.9 %/92.3 %) for achieving pVL <200 copies/mL at 96 weeks.

Conclusions

A higher rate of EFV-related adverse events and discontinuations due to these events for EFV600 were not driven by polymorphisms assessed. Although a single threshold concentration associated with HIV suppression may be clinically useful, it was not viable for ENCORE1. Implementation of EFV400 would improve toxicity management whilst still maintaining good efficacy.

Electronic supplementary material

The online version of this article (doi:10.1007/s40262-015-0360-5) contains supplementary material, which is available to authorized users.

Impact of Single Nucleotide Polymorphisms on Plasma Concentrations of Efavirenz and Lopinavir/Ritonavir in Chinese Children Infected with the Human Immunodeficiency Virus

Single nucleotide polymorphisms (SNPs) in the genes that encode the cytochrome P450 (CYP) drug metabolizing enzymes and drug transporters have been reported to influence antiretroviral drug pharmacokinetics. Although primarily metabolized by CYP2B6 and -3A, efavirenz (EFV) and lopinavir/ritonavir (LPV/r) are substrates of P-glycoprotein and the solute carrier organic (SLCO) anion transporter, respectively. We investigated the association between SNPs and efavirenz (EFV) or lopinavir/ritonavir (LPV/r) concentrations in Chinese children infected with the human immunodeficiency virus (HIV). Genotyping was performed on CYP2B6 516G→T, -1459C→T, and -983T→C, ABCB1 3435C→T, and SLCO1B1 521T→C in 229 HIV-infected Chinese pediatric patients (age range 4.0 to 17.5 yrs). Plasma concentrations of EFV and LPV/r were measured using validated high-performance liquid chromatography coupled with the mass spectrum method among 39 and 69 children who received EFV- and LPV/r-containing regimens, respectively. The frequencies of CYP2B6 516G→T in the study participants were 71%, 25%, and 4% for the G/G, G/T, and T/T genotypes, respectively. Among the children under therapeutic drug monitoring, 21% and 39% experienced EFV and LPV concentrations, respectively, above the upper threshold of the therapeutic window. CYP2B6 516G→T was significantly associated with EFV concentrations (p<0.001). Older children (older than 10 yrs) were more likely to have significantly higher EFV concentrations than the younger ones (p=0.0314). CYP2B6 genotyping and EFV concentration monitoring may help optimize antiretroviral therapy in pediatric patients who initiate an EFV-based regimen.

When could new antiretrovirals be recommended for national treatment programmes in low-income and middle-income countries: results of a WHO Think Tank

PURPOSE OF REVIEW

To discuss barriers and opportunities for the introduction of new antiretrovirals into national treatment programmes in low-income and middle-income countries to support further treatment scale-up. Invitees to a WHO Think Tank in February 2017 evaluated recently published results.

RECENT FINDINGS

There is not sufficient clinical experience of dolutegravir (DTG), tenofovir alafenamide (TAF) or efavirenz 400 mg (EFV400) to recommend their use in pregnancy. Outcomes from births and assessment of congenital anomalies need to be evaluated from several hundred pregnant women. Clinical experience of these treatments during rifampicin-based treatment for tuberculosis is also required. This could be difficult for TAF, which is currently contraindicated with TAF. Changes in second-line treatment from two nucleoside analogues + protease inhibitor plus ritonavir will require new randomized trials of alternative combinations.

CONCLUSION

Additional safety and efficacy data on DTG, TAF and EFV400 in some subpopulations are needed before a large introduction in national treatment programmes. There is currently limited support for the introduction of TAF as part of first-line antiretroviral treatment in low-income and middle-income settings. There was an overall agreement for 6-monthly reviews of safety and efficacy data, in parallel with a phased introduction of the new antiretrovirals.

Plasma Efavirenz Exposure, Sex, and Age Predict Virological Response in HIV-Infected African Children

BACKGROUND

Owing to insufficient evidence in children, target plasma concentrations of efavirenz are based on studies in adults. Our analysis aimed to evaluate the pediatric therapeutic thresholds and characterize the determinants of virological suppression in African children.

METHODS

We analyzed data from 128 African children (aged 1.7-13.5 years) treated with efavirenz, lamivudine, and one among abacavir, stavudine, or zidovudine, and followed up to 36 months. Individual pharmacokinetic (PK) measures [plasma concentration 12 hours after dose (C12h), plasma concentration 24 hours after dose (C24h), and area under the curve (AUC0-24)] were estimated using population PK modeling. Cox multiple failure regression and multivariable fractional polynomials were used to investigate the risks of unsuppressed viral load associated with efavirenz exposure and other factors among 106 initially treatment-naive children, and likelihood profiling was used to identify the most predictive PK thresholds.

RESULTS

The risk of viral load >100 copies per milliliter decreased by 42% for every 2-fold increase in efavirenz mid-dose concentration [95% confidence interval (CI): 23% to 57%; P < 0.001]. The most predictive PK thresholds for increased risk of unsuppressed viral load were C12h 1.12 mg/L [hazard ratio (HR): 6.14; 95% CI: 2.64 to 14.27], C24h 0.65 mg/L (HR: 6.57; 95% CI: 2.86 to 15.10), and AUC0-24 28 mg·h/L (HR: 5.77; 95% CI: 2.28 to 14.58). Children older than 8 years had a more than 10-fold increased risk of virological nonsuppression (P = 0.005); among children younger than 8 years, boys had a 5.31 times higher risk than girls (P = 0.007). Central nervous system adverse events were infrequently reported.

CONCLUSIONS

Our analysis suggests that the minimum target C24h and AUC0-24 could be lowered in children. Our findings should be confirmed in a prospective pediatric trial.