Comparison of the plasma pharmacokinetics of lamivudine during twice and once daily administration in patients with HIV

Population pharmacokinetic modeling of dolutegravir/lamivudine to support a once-daily fixed-dose combination regimen in virologically suppressed adults living with HIV-1

A fixed-dose combination (FDC) of 50 mg dolutegravir and 300 mg lamivudine is indicated for the treatment of HIV-1 infection. This analysis aimed to characterize the population pharmacokinetics (PK) of dolutegravir and lamivudine based on data from a phase 3 study (TANGO) in virologically suppressed adults living with HIV-1 switching to dolutegravir/lamivudine FDC. These analyses included 362 participants who contributed 2,629 dolutegravir and 2,611 lamivudine samples collected over 48 weeks. A one-compartment model with first-order absorption and elimination parameterized by apparent oral clearance (CL/F), apparent volume of distribution (V/F), and absorption rate constant (Ka) described dolutegravir PK. Covariate search yielded body weight, bilirubin, and ethnicity as predictors of CL/F, and weight was predictive for V/F. The estimates of CL/F, V/F, and Ka were 0.858 L/h, 16.7 L, and 2.15 h-1, respectively. A two-compartment model with first-order absorption and elimination parameterized by CL/F, apparent intercompartmental clearance (Q/F), apparent central volume of distribution (V2/F), apparent peripheral volume of distribution (V3/F), and Ka described lamivudine PK. Covariate search yielded eGFR and race as predictors of CL/F, and weight was predictive for V2/F. The estimated parameter values were CL/F = 19.6 L/h, Q/F = 2.97 L/h, V2/F = V3/F = 105 L, and Ka = 2.30 h-1. The steady-state prediction suggested that the effect of covariates dolutegravir and lamivudine exposures was small (<20%) and not clinically relevant. Therefore, no dose adjustments are recommended based on these analyses. The results support the use of dolutegravir/lamivudine FDC in the treatment of HIV-1 infection in adults.CLINICAL TRIALSThis study is registered with ClinicalTrials.gov as NCT03446573.

Factors influencing hair lamivudine concentration among people living with HIV in Guangxi, China

BACKGROUND

Hair antiretroviral concentration has served as an innovative and objective measure of antiretroviral adherence. However, some factors (for example, pharmacokinetics and hair characteristics) may contribute to the variability of hair antiretroviral concentration that may threaten the validity and reliability of the hair measure as a biomarker of adherence. This study aimed to examine the potential factors that may influence the measure of hair antiretroviral concentration.

METHODS

Hair samples from a cohort of 372 people living with HIV (PLHIV) receiving lamivudine (300 mg/day) in Guangxi, China. Lamivudine concentration was analysed using liquid chromatography-tandem mass spectrometry. Multivariable linear regression was used to evaluate the associations of hair lamivudine concentration with age, sex, ethnicity, height, weight, body mass index, duration of HIV diagnosis, duration of current regimen, dosing schedule, concomitant antiretroviral medications, frequency of hair washing, hair care products use, hair cosmetic treatment and self-reported adherence.

RESULTS

Multivariable models revealed that frequency of hair washing (β=-0.221, P=0.001), dosing schedule (β=0.141, P=0.036) and self-reported adherence (β=0.160, P=0.002) were associated with hair lamivudine concentration.

CONCLUSIONS

We observed that, among those potential factors, hair lamivudine concentration was influenced by frequency of hair washing and dosing schedule. Therefore, frequency of hair washing and dosing schedule should be considered in future research using hair lamivudine concentration as a measure of lamivudine exposure and biomarker of adherence.

Lamivudine/Tenofovir Disoproxil Fumarate is an Appropriate PrEP Regimen

Oral pre-exposure prophylaxis (PrEP) containing tenofovir disoproxil fumarate (TDF) co-formulated with emtricitabine (FTC) or lamivudine (3TC) is recommended as an additional prevention option for persons at substantial risk of HIV infection by both the World Health Organization (WHO) and the US President's Emergency Plan for AIDS Relief (PEPFAR). The WHO and PEPFAR consider 3TC clinically interchangeable with FTC for PrEP given comparable pharmacologic equivalence, resistance and toxicity patterns, and indirect clinical trial evidence from TDF-containing studies. Globally, FTC/TDF has been widely used in clinical trials, open-label extension studies and demonstration projects. Thus, most PrEP efficacy and safety data are based on FTC/TDF use in heterosexual women and men, men who have sex with men, and people who inject drugs. However, generic 3TC/TDF is less expensive than FTC/TDF, is already available in supply chains for HIV drugs, and has 60-70% of the global adult market share, making it particularly appealing in settings with limited availability or affordability of FTC/TDF. Compelling indirect evidence suggests that scaling up use of 3TC/TDF is potentially cost saving for HIV programs in settings where restricting drug choice to FTC/TDF would delay PrEP implementation. Guideline committees and public health decision-makers in countries should encourage flexibility in PrEP drug selection, support off-label use of 3TC/TDF, and approve use of generic formulations to decrease the cost of PrEP medications and accelerate PrEP delivery through the public and private sectors.

The effect of veno-arterial extracorporeal oxygenation and nasogastric tube administration on the pharmacokinetic profile of abacavir, lamivudine and dolutegravir: a case report

BACKGROUND

Pharmacokinetic (PK) changes can affect antiretroviral (ARV) systemic exposure for critically ill patients living with HIV (CI-PLWH). Studies to guide ARV adjustments in this population are limited.

METHODS

A PK analysis was conducted in a 44-year-old CI-PLWH who presented for a heart and lung transplant on veno-arterial extracorporeal membrane oxygenation (VA ECMO). Home ARV therapy (ART) of co-formulated abacavir/lamivudine/dolutegravir (ABC/3TC/DTG) was continued. ARV serum concentrations were obtained during and after VA ECMO. Two blood levels were drawn at 1 h, for maximum serum concentration (C_max) and a serum trough (C_t). ARVs were given as a single tablet crushed via nasogastric tube.

RESULTS

Area under the concentration-time curve (AUC_0-t) was calculated using non-compartmental analysis. C_max and AUC_0-t were higher during VA ECMO compared with post-decannulation. The C_max of ABC was >2.5-fold higher than the mean in the reference. C_max and C_t post VA ECMO were within range of referenced literature for all ARVs. C_max and AUC_0-t of DTG post VA ECMO was approximately four- to fivefold lower than referenced literature. HIV virological suppression was maintained throughout the hospitalization.

CONCLUSIONS

ART adjustments would not be required for this patient. Additional studies are needed to assess effects of VA ECMO and crushed tube administration of ARVs in CI-PLWH.

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.

Synthesis and characterization of a long-acting emtricitabine prodrug nanoformulation

Purpose

A palmitoylated prodrug of emtricitabine (FTC) was synthesized to extend the drug’s half-life, antiretroviral activities and biodistribution.

Methods

A modified FTC prodrug (MFTC) was synthesized by palmitoyl chloride esterification. MFTC’s chemical structure was evaluated by nuclear magnetic resonance. The created hydrophobic prodrug nanocrystals were encased into a poloxamer surfactant and the pharmacokinetics (PK), biodistribution and antiretroviral activities of the nanoformulation (NMFTC) were assessed. The conversion of MFTC to FTC triphosphates was evaluated.

Results

MFTC coated with poloxamer formed stable nanocrystals (NMFTC). NMFTC demonstrated an average particle size, polydispersity index and zeta potential of 350 nm, 0.24 and −20 mV, respectively. Drug encapsulation efficiency was 90%. NMFTC was readily taken up by human monocyte-derived macrophages yielding readily detected intracellular FTC triphosphates and an extended PK profile.

Conclusion

NMFTC shows improved antiretroviral activities over native FTC. This is coordinate with its extended apparent half-life. The work represents an incremental advance in the development of a long-acting FTC formulation.

Twenty-Five Years of Lamivudine: Current and Future Use for the Treatment of HIV-1 Infection

Supplemental Digital Content is Available in the Text.

Innovation in medicine is a dynamic, complex, and continuous process that cannot be isolated to a single moment in time. Anniversaries offer opportunities to commemorate crucial discoveries of modern medicine, such as penicillin (1928), polio vaccination (inactivated, 1955; oral, 1961), the surface antigen of the hepatitis B virus (1967), monoclonal antibodies (1975), and the first HIV antiretroviral drugs (zidovudine, 1987). The advent of antiretroviral drugs has had a profound effect on the progress of the epidemiology of HIV infection, transforming a terminal, irreversible disease that caused a global health crisis into a treatable but chronic disease. This result has been driven by the success of antiretroviral drug combinations that include nucleoside reverse transcriptase inhibitors such as lamivudine. Lamivudine, an L-enantiomeric analog of cytosine, potently affects HIV replication by inhibiting viral reverse transcriptase enzymes at concentrations without toxicity against human polymerases. Although lamivudine was approved more than 2 decades ago, it remains a key component of first-line therapy for HIV because of its virological efficacy and ability to be partnered with other antiretroviral agents in traditional and novel combination therapies. The prominence of lamivudine in HIV therapy is highlighted by its incorporation in recent innovative treatment strategies, such as single-tablet regimens that address challenges associated with regimen complexity and treatment adherence and 2-drug regimens being developed to mitigate cumulative drug exposure and toxicities. This review summarizes how the pharmacologic and virologic properties of lamivudine have solidified its role in contemporary HIV therapy and continue to support its use in emerging therapies.

Evaluation of effect of impaired renal function on lamivudine pharmacokinetics

AIMS

This study aimed to describe lamivudine pharmacokinetics in patients with impaired renal function and to evaluate the consistency of current dosing recommendations.

METHODS

A total of 244 patients, ranging in age from 18 to 79 years (median 40 years) and in bodyweight from 38 to 117 kg (median 71 kg), with 344 lamivudine plasma concentrations, were analysed using a population pharmacokinetic analysis. Serum creatinine clearance (CLCR) was calculated using the Cockcroft-Gault formula; 177 patients had normal renal function (CLCR > 90 ml min(-1) ), 50 patients had mild renal impairment (CLCR = 60-90 ml min(-1) ), 20 patients had moderate renal impairment (CLCR = 30-60 ml min(-1) ), and five patients had severe renal impairment (CLCR < 30 ml min(-1) ).

RESULTS

A two-compartment model adequately described the data. Typical population estimates (percentage interindividual variability) of the apparent clearance (CL/F), central (Vc /F) and peripheral volumes of distribution (Vp /F), intercompartmental clearance (Q/F) and absorption rate constant (Ka ) were 29.7 l h(-1) (32%), 68.2 l, 114 l, 10.1 l h(-1) (85%) and 1 h(-1) , respectively. Clearance increased significantly and gradually with CLCR. Our simulations showed that a dose of 300 mg day(-1) in patients with mild renal impairment could overexpose them. A dose of 200 mg day(-1) maintained an exposure close to that of adults with normal renal function. However, the current US Food and Drug Administration recommendations for lamivudine in other categories of patients (from severe to moderate renal impairment) provided optimal exposures.

CONCLUSIONS

Lamivudine elimination clearance is related to renal function. To provide optimal exposure, patients with mild renal impairment should receive 200 mg day(-1) instead of 300 mg day(-1) .

Association of Nevirapine Levels with Rash or Hepatotoxicity Among HIV-Infected Thai Women

BACKGROUND

We performed a nested case-control study of Thai women prescribed nevirapine-based antiretroviral therapy (ART) to determine if development of rash or hepatotoxicity during the first 24 weeks of treatment is associated with plasma nevirapine concentrations.

METHOD

From May 2005-January 2007, we enrolled 217 women initiating nevirapine-based ART in Thailand. Cases (n = 54) were women who during the first 24 weeks of treatment with nevirapine developed rash (any grade, n = 42) or hepatotoxicity (≥grade 2, n = 22, [10 had both]). Controls were the next enrolled woman who was confirmed not to meet the case definition during the first 24 weeks. Nevirapine concentrations after the two week lead-in dose of 200 mg once daily were compared between cases and controls by Wilcoxon rank-sum tests.

RESULTS

We found no difference in Week 2 pre-dose nevirapine concentrations: cases median = 3,528 ng/mL (n = 24), controls median = 3,150ng/mL (n = 30), p = 0.5. Cases had higher post-dose nevirapine concentrations (median = 6,150 ng/mL, n = 21) than controls (median = 4,746 ng/mL, n = 20, p = 0.02). When limited to cases who developed a rash at Week 2, we found no differences in the pre-dose (median = 3,270 ng/mL, n = 12, p = 0.9) or post-dose nevirapine concentration (median = 5,443 ng/mL, n = 9, p = 0.4) compared with controls.

CONCLUSIONS

We cannot conclude definitively that nevirapine concentrations at two weeks of therapy are associated with rash or hepatotoxicity. It is unlikely that therapeutic drug monitoring at that time will improve identification of patients at risk for rash or hepatotoxicity.

Developmental pharmacokinetic changes of Lamivudine in infants and children

Lamivudine is a nucleoside reverse transcriptase inhibitor widely used in infants and children in combination antiretroviral therapy to treat human immunodeficiency virus (HIV) infection. Developmental changes in lamivudine pharmacokinetic disposition were assessed by combining data from 7 studies of lamivudine (Pediatric AIDS Clinical Trials Group 300, 353, 356, 358, 386, 1056, and 1069) representing subjects across the pediatric age continuum. A population pharmacokinetic model was developed to identify factors that influence lamivudine disposition. Age and Thai race were independent predictors of apparent clearance (CL/F), whereas the use of a fixed drug combination formulation (GPO-VIR) was an independent predictor of bioavailability, with CL/F more than doubling from birth to adolescence. Serum creatinine was not associated with CL/F. Monte Carlo simulations were used to compare the lamivudine exposure achieved with World Health Organization (WHO) weight band and Food and Drug Administration (FDA) label dosing recommendations. WHO dosing yielded higher exposure during the first few months of life, but this difference was less pronounced between 6 months and 14 years of age. Overall, both FDA and WHO dosing provided similar AUC values to those previously reported in HIV-infected adults. Lamivudine WHO weight band dosing results in therapeutic exposure in infants and children and may improve drug dosing in resource-limited countries.

Pharmacokinetics and safety of a new paediatric fixed-dose combination of zidovudine/lamivudine/nevirapine in HIV-infected children

BACKGROUND

Alternatives to the available stavudine-containing paediatric fixed-dose combination (FDC) tablets are rapidly needed due to concerns regarding the cumulative toxicity of long-term stavudine exposure. We report the bioavailability and short-term safety of a novel paediatric FDC tablet of zidovudine (ZDV)/lamivudine (3TC)/nevirapine (NVP; 30/15/28 mg) in HIV-infected children.

METHODS

In this Phase I/II open-label pharmacokinetic study, 42 children weighing 6-30 kg treated with NVP-based HAART for ≥4 weeks were randomized to receive the FDC tablets (GPO-VIR Z30) or the liquid formulations. Dosing was weight-based. Intensive 12-h blood sampling was performed after 2 weeks; subjects then crossed-over to the alternate formulation at equal doses and sampling repeated 2 weeks later. Pharmacokinetic parameters were determined by non-compartmental analysis. Buccal-swab samples were collected for cytochrome P450 (CYP)2B6 polymorphism analysis.

RESULTS

With the FDC tablet, the geometric mean (90% CI) area under the curve (AUC) for ZDV, 3TC and NVP was 1.58 (1.49-1.68), 7.78 (7.38-8.19) and 68.88 (62.13-76.36) μg•h/ml, respectively. Rules for NVP therapeutic inadequacy were defined a priori, and despite lower NVP exposure with the tablet (P<0.001), the levels remained therapeutically adequate. ZDV AUC was similar between formulations. 3TC exposure was significantly higher with the tablet but comparable to historical data in adults and children taking branded tablets. While receiving the tablet, NVP AUC in children with CYP2B 516 GG (45%), GT (45%) and TT (10%) genotypes were 67.0, 74.5 and 106.4 μg•h/ml, respectively (P=0.04).

CONCLUSIONS

Disparities in drug exposure between formulations were observed; however, the FDC tablet delivered therapeutically adequate exposures of each drug and could well play an important role in simplifying antiretroviral treatment for children.

Pharmacokinetics of antiretroviral drug varies with formulation in the target population of children with HIV-1

The bioequivalence of formulations is usually evaluated in healthy adult volunteers. In our study in 19 HIV-1-infected Ugandan children (1.8-4 years of age, weight 12 to <15 kg) receiving zidovudine, lamivudine, and abacavir solutions twice a day for ≥24 weeks, the use of scored tablets allowed comparison of plasma pharmacokinetics of oral solutions vs. tablets. Samples were collected 0, 1, 2, 4, 6, 8, and 12 h after each child's last morning dose of oral solution before changing to scored tablets of Combivir (coformulated zidovudine + lamivudine) and abacavir; this was repeated 4 weeks later. Dose-normalized area under curve (AUC)(0-12) and peak concentration (C(max)) for the tablet formulation were bioequivalent with those of the oral solution with respect to zidovudine and abacavir (e.g., dose-normalized geometric mean ratio (dnGMR) (tablet:solution) for zidovudine and abacavir AUC(0-12) were 1.01 (90% confidence interval (CI) 0.87-1.18) and 0.96 (0.83-1.12), respectively). However, lamivudine exposure was ~55% higher with the tablet formulation (AUC(0-12) dnGMR = 1.58 (1.37-1.81), C(max) dnGMR = 1.55 (1.33-1.81)). Although the clinical relevance of this finding is unclear, it highlights the impact of the formulation and the importance of conducting bioequivalence studies in target pediatric populations.

Abacavir and lamivudine for the treatment of human immunodeficiency virus

INTRODUCTION

The introduction of combination antiretroviral therapy (cART) in 1996 dramatically changed the survival and the quality of life of people living with human immunodeficiency virus (HIV). Viral replication can be controlled by using a combination of more than 30 licensed drugs. Despite the fact that many advances have been made in the last 20 years of experience with antiretrovirals, certain needs remain to be addressed, such as the presence of chronic inflammation, the long-term side effects of newly introduced drugs and eradication. Abacavir (ABC) and lamivudine (3TC) are licensed in a fixed-dose combination to be administered once daily with other antiretroviral agents for the treatment of HIV.

AREAS COVERED

This article provides an extensive review of the evidence on the combination of ABC 600 mg and 3TC 300 mg. Specifically, it discusses the chemistry-- including the phrarmacodynamics, resistance to treatment, pharmacokinetics and metabolism--and formulations available. It also looks at clinical efficacy, including safety and tolerability.

EXPERT OPINION

In the last few years, new data regarding human leukocyte antigen (HLA) B*5701 testing to prevent the hypersensitivity reaction due to ABC have been presented, providing a landmark in the management of adverse events in HIV, and later a previously unexpected correlation of the recent exposure to ABC with an increased risk of cardiovascular disease. This review presents the current situation with regard to the long-term efficacy and safety data on the ABC/3TC combination.

Developmental pharmacokinetics of lamivudine in 580 pediatric patients ranging from neonates to adolescents

Lamivudine concentration-time courses were described for a very large range of ages to study the effects of body weight and maturation on lamivudine pharmacokinetics and to check the consistency of dosing recommendations. Lamivudine concentrations were monitored on a routine basis to produce concentrations similar to the known values in adults. Concentrations were measured in 580 children from 2 days to 18 years old. A total of 2,106 plasma lamivudine concentrations were measured, and a population pharmacokinetic analysis was performed using the stochastic approximation expectation maximization algorithm implemented in MONOLIX 3.1 software. A two-compartment model adequately described the data. After standardization for a mean standard body weight by using an allometric model, age also had a significant effect on clearance maturation. Typical population estimates (percent interindividual variability) standardized for 70 kg of the apparent clearance, including central and peripheral volumes of distribution, intercompartmental clearance, and absorption rate constant, were 31 liters · h(-1) (32%), 76.4 liters (77%), 129 liters, 5.83 liters · h(-1), and 0.432 h(-1), respectively. According to the model, elimination clearance (liters/h/70 kg) increases gradually during the first years of life. Theoretical doses needed to reach the range of 24 h of exposure observed in adults were calculated: to be closer to adult exposure, children should receive 4 mg/kg/day from birth to 8 weeks of age, 5 mg/kg/day from 8 to 16 weeks of age, 6 mg/kg from 16 to 25 weeks of age, 8 mg/kg/day from 25 weeks of age to 14 kg of body weight, 150 mg/day from 14 to 25 kg of body weight, 225 mg/day from 25 to 35 kg of body weight, and 300 mg/day thereafter.

Pharmacokinetics and acceptability of once- versus twice-daily lamivudine and abacavir in HIV type-1-infected Ugandan children in the ARROW Trial

BACKGROUND

No data on once-daily dosing of nucleoside analogues in African children currently exist. We compared the pharmacokinetics (PK) of once- versus twice-daily lamivudine and abacavir treatment using the World Health Organization recommended weight band dosing of scored adult tablets.

METHODS

HIV type-1 (HIV-1)-infected Ugandan children aged 3-12 years receiving antiretroviral therapy that included lamivudine and abacavir twice daily (total 150+300 mg, 225+450 mg and 225/300+600 mg daily for 12-<20, 20-<25 and ≥25 kg, respectively) were enrolled in a crossover study. Plasma PK sampling (at 0, 1, 2, 4, 6, 8 and 12 h after observed morning intake) was performed for the twice-daily regimen at steady-state. Children were then switched to once-daily treatment with PK sampling repeated 4 weeks later (with an additional 24 h sample). Acceptability questionnaires were completed at both time points. Daily area under the curve (AUC(0-24)) and maximum concentrations (C(max)) were compared by geometric mean ratios (GMRs).

RESULTS

A total of 41 HIV-1-infected children (median age of 7 years) and n=23, n=14 and n=4 in 12-<20, 20-<25 and ≥25 kg weight bands, respectively, were enrolled. Mean AUC(0-24) was 13.0 and 12.0 mg•h/l for once- and twice-daily lamivudine (GMR 1.09, 90% confidence intervals [CI] 0.98-1.20) and 15.3 and 15.6 mg•h/l for once- and twice-daily abacavir (GMR 0.98, 90% CI 0.89-1.08), respectively, with no difference in 3-6 versus 7-12 year olds. C(max) was 76% (lamivudine) and 64% (abacavir) higher on once-daily regimens. For both children and caregivers, once-daily dosing of lamivudine plus abacavir was highly acceptable and strongly preferred over twice-daily.

CONCLUSIONS

In children aged 3-12 years, AUC(0-24) of lamivudine and abacavir were bioequivalent on once- and twice-daily regimens. Once-daily dosing of abacavir and lamivudine could provide an alternative dosing strategy for HIV-1-infected children, with high acceptability and strong preference suggesting the potential for improved adherence.

Steady-state pharmacokinetics of lamivudine once-daily versus twice-daily dosing in Chinese HIV-infected patients

OBJECTIVE

The present study aimed to compare the pharmacokinetics of lamivudine in 300 mg once-daily and 150 mg twice-daily dosing regimens in HIV-infected Chinese patients.

METHODS

HIV-infected patients received lamivudine 300 mg once daily or 150 mg twice daily as part of a highly active antiretroviral therapy regimen. After the patients received lamivudine for at least 3 months, serial blood samples were collected for 24 hours. The samples were measured by a validated high-performance liquid chromatography (HPLC) assay. The pharmacokinetics of once-daily versus twice-daily dosing was evaluated by noncompartment models.

RESULTS

Ten patients received lamivudine 300 mg once daily and 5 patients received 150 mg twice daily. The C(max) was significantly higher in the once-daily arm than the twice-daily arm (2.23 vs 1.61 μg/mL, P <.05), whereas the C(min) was markedly lower (0.05 vs 0.12 μg/mL, P <.05). The half-lives were 3.32 hours and 2.62 hours, and AUC₂₄ values were 11.8 μg/mL·h and 13.0 μg/mL·h in the 300 mg once-daily and 150 mg twice-daily regimens, respectively (P >.05).

CONCLUSION

The shorter half-life was observed first in Chinese HIV patients with once- and twice-daily regimens. The 300 mg once-daily regimen was associated with lower trough concentrations and remarkable interpatient variability. Further studies in large groups of HIV patients are needed to confirm the influence of shorter half-lives in Chinese patients on efficacy and toxicity.

A chewable pediatric fixed-dose combination tablet of stavudine, lamivudine, and nevirapine: pharmacokinetics and safety compared with the individual liquid formulations in human immunodeficiency virus-infected children in Thailand

BACKGROUND

Pediatric fixed-dose combinations (FDCs) are needed to facilitate antiretroviral therapy in children. We evaluated the relative bioavailability, safety, and therapeutic adequacy of a novel chewable pediatric FDC tablet of stavudine (7 mg), lamivudine (30 mg), and nevirapine (50 mg), referred to as GPO-VIR S7, and compared it with the individual original brand-name liquid formulations in human immunodeficiency virus-infected Thai children.

METHODS

The International Maternal Pediatric Adolescent AIDS Clinical Trials group (IMPAACT) P1056 study was a phase I/II, 2-arm, randomized, open-label, multidose pharmacokinetic cross-over study. Children ≥6 to ≤30 kg receiving nevirapine-based HAART for at least 4 weeks were randomized to receive GPO-VIR S7 chewable tablets or the equivalent liquid formulations. Children were stratified by weight and dosing was weight-based. Intensive 12-hour blood sampling was performed on day 28, and subjects then crossed-over to the alternate formulation at equal doses with identical 12-hour sampling on day 56. Pharmacokinetic indices were determined by noncompartmental analysis.

RESULTS

Thirty-four children completed the study. While taking Government Pharmaceutical Organization (GPO)-VIR S7 the geometric mean (90% CI) area under the curve was 1.54 μg·hr/mL (1.42-1.67) for stavudine, 6.39 (5.82-7.00) for lamivudine, and 74.06 (65.62-83.60) for nevirapine. Nevirapine drug exposure for GPO-VIR S7 was therapeutically adequate. Geometric mean area under the curve ratios (90% CI) of GPO-VIR S7/liquid formulation for stavudine, lamivudine, and nevirapine were 0.97 (0.92-1.02), 1.41 (1.30-1.53), and 1.08 (1.04-1.13), respectively. No serious drug-related toxicity was reported.

CONCLUSIONS

The chewable FDC was safe and provided therapeutically adequate plasma drug exposures in human immunodeficiency virus-infected children. Substituting the FDC for liquid formulations can simplify antiretroviral therapy.

Abacavir/lamivudine combination in the treatment of HIV: a review

Abacavir has been at the center of research and clinical interest in the last two years. The frequency of the associated abacavir hypersensitivity syndrome has decreased substantially since the introduction of routine testing for the HLA-B*5701 allele; the activity of the drug in HIV-infected persons with HIV RNA values more than 100,000 copies/mL has been questioned; the possible increased risk of myocardial infarction after recent exposure to abacavir has been debated; and the drug has been moved from the “recommended” category to the “alternative” category in several guidelines. Still, the drug remains a useful agent in combination with other drugs, including lamivudine, for the treatment of HIV infection. This review will focus on the pharmacokinetics, activity, side effects, and resistance profile of both abacavir and lamivudine, including a thorough review of all of the recent studies relevant to both drugs.

Abacavir/lamivudine fixed-dose combination antiretroviral therapy for the treatment of HIV

In the past 15 years, improvements in the treatment of HIV infection have dramatically reduced morbidity and mortality. Nucleoside reverse transcriptase inhibitors are the backbone of combination antiretroviral therapy for the treatment of HIV. One of the recommended and commonly used therapies in this class is the once-daily fixed-dose combination of abacavir/lamivudine. Clinical studies and practice have shown these drugs to be potent, safe, and easy to use in a variety of settings; however, several recent reports have challenged the safety and efficacy claims among certain patient populations, including those at risk for cardiovascular disease and in those with high viral loads prior to treatment initiation. We reviewed abacavir/lamivudine as a treatment for HIV and discussed limitations of its use due to these controversial issues.

Population pharmacokinetics of lamivudine in human immunodeficiency virus-exposed and -infected infants

This study aimed to determine lamivudine disposition in infants and to construct an appropriate dose adjustment for age, given the widespread use of lamivudine for both the prevention of mother-to-child transmission of human immunodeficiency virus (HIV) and the treatment of HIV-infected infants. Using a pooled-population approach, the pharmacokinetics of lamivudine in HIV-exposed or -infected infants from four Pediatric AIDS Clinical Trials Group studies were assessed. Ninety-nine infants provided 559 plasma samples for measurement of lamivudine concentrations. All infants received combination antiretroviral therapy including lamivudine dosed at 2 mg/kg of body weight every 12 h (q12h) for the first 4 to 6 weeks of life and at 4 mg/kg q12h thereafter. Lamivudine's apparent clearance was 0.25 liter/h/kg at birth, doubling by 28 days. In the final model, age and weight were the only significant covariates for lamivudine clearance. While lamivudine is predominantly renally eliminated, the serum creatinine level was not an independent covariate in the final model, possibly because it was confounded by age. Inclusion of interoccasion variability for bioavailability improved the individual subject clearance prediction over the age range studies. Simulations based on the final model predicted that by the age of 4 weeks, 90% of infant lamivudine concentrations with the standard 2 mg/kg dose of lamivudine fell below the adult median concentration. This population pharmacokinetic analysis affirms that adjusting the dose of lamivudine from 2 mg/kg to 4 mg/kg q12 h at the age of 4 weeks for infants with normal maturation of renal function will provide optimal lamivudine exposure, potentially contributing to more successful therapy.

Age-dependent pharmacokinetics of lamivudine in HIV-infected children

The recommended dose of lamivudine in children is higher when compared with adults: 4 mg/kg vs approximately 2 mg/kg (150 mg) and administered twice a day. Limited data are available to demonstrate that this increased dose results in adequate exposure to lamivudine in children with human immunodeficiency virus (HIV) infection. Data were selected from children who were using lamivudine for at least 2 weeks before a full pharmacokinetic (PK) study was conducted. Lamivudine PK parameters were significantly related to age. The age of 6 years appeared to be a cutoff for a change in PK parameters of lamivudine, with children <6 years of age (n=17) having a median area under the curve 43% lower and a median peak plasma concentration 47% lower (both P<0.001) than older children (n=34). In conclusion, further investigation of the relationship between decreased lamivudine exposure and treatment outcome and long-term resistance development in younger children with HIV infection is warranted.

Abacavir/lamividune combination in the treatment of HIV-1 infection: a review

Consensus guidelines for the management of HIV infection recommend the use of two nucleoside analogues in combination with either a non-nucleoside reverse transcriptase inhibitor or a ritonavir-boosted protease inhibitor in therapy-naive patients. As adherence is crucial for treatment success, regimens with fewer pills, simpler dosing schedules and fewer adverse events have become the first choice for antiretroviral therapy. Fixed-dose combinations further improve the convenience of therapy. There are three dual-nucleoside fixed-dose combinations licensed for treating HIV-infected individuals, which include a combination of abacavir and lamivudine. This article reviews the pharmacology, efficacy, resistance profiles, safety and tolerability of abacavir focussing on its use in combination with lamivudine and discusses the role of this nucleoside backbone in antiretroviral therapy.

Early virologic failure and rescue therapy of tenofovir, abacavir, and lamivudine for initial treatment of HIV-1 infection: TONUS study

BACKGROUND

To assess the efficacy and safety of the triple NRTI combination of abacavir (ABC), lamivudine (3TC), and tenofovir (TDF) in a once-daily regimen.

METHOD

38 HIV-naive patients (pts) were treated in a prospective open-arm study over 48 weeks (W48). Virological failure was defined as never achieving plasma HIV-1 RNA < 400 copies/mL or rebound of > or = 0.7 log10.

RESULTS

12/36 (33%) pts had virologic failure at W24 and 10 additional pts had HIV RNA > 50 copies/mL at W12 or W24. There was a significant association between baseline viral load (VL) and virologic failure in 0%, 29%, and 64% pts with baseline VL levels < 4, 4-5, and > 5 log10 copies/mL, respectively (p = .014). 76% of pts developed K65R and M184V/I mutations by W24, and 19% developed M184V/I alone. At W4, 86% of pts had adequate plasma Cmin for the 3 drugs. 14 pts with K65R and M184V/I were given a rescue therapy with a successful outcome (< 50 copies/mL; median follow-up 48 weeks).

CONCLUSION

Convergent genetic pathway to resistance, in conjunction with lower antiretroviral potency, may explain the high rate of selection K65R and M184V mutations. These mutations did not appear to have a negative effect on rescue therapy with a variety of regimens.

Pharmacokinetic properties of nucleoside/nucleotide reverse transcriptase inhibitors

Options for antiretroviral therapy in patients infected with HIV continue to expand as new drugs are integrated into treatment regimens. Nonetheless, nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs/NtRTIs) remain the backbone of highly active antiretroviral therapy (HAART). With the approval of emtricitabine in 2003, there are now 8 Food and Drug Administration (FDA)-approved NRTIs/NtRTIs. Several of these agents are effective as once-daily therapy, including didanosine, lamivudine, extended-release stavudine (FDA approved, but not currently available), tenofovir DF, and emtricitabine. Recent results from pharmacokinetic and clinical trials indicate that another NRTI, abacavir, may also be effective as a once-daily therapy, and FDA approval of once-daily dosing is anticipated. NRTIs are inactive as administered, requiring anabolic phosphorylation within target cells to achieve their antiretroviral effects. All NRTIs are converted to nucleoside triphosphates, which serve as the active metabolites (the NtRTI, tenofovir DF, only requires conversion to the diphosphate form). Frequency of drug administration is closely related to the pharmacokinetic properties of a drug. The key parameter is the half-life; however, the plasma elimination half-life of the NRTIs/NtRTIs as administered is of little use in developing a dosing schedule. Rather, the intracellular half-life of the nucleoside triphosphate is the relevant parameter. This article reviews the pharmacokinetic properties, particularly those of the various phosphorylation steps, of the NRTIs/NtRTIs.

The pharmacology of antiretroviral nucleoside and nucleotide reverse transcriptase inhibitors: implications for once-daily dosing

The trend toward once-daily dosing in HIV antiretroviral therapy is based on the association between adherence, treatment outcome, and patient preferences. Patients prefer simpler treatments, fewer pills, less frequent dosing, and no food restrictions. When a regimen meets a patient's preferences, the patient is more likely to be adherent, and with good adherence, the regimen is more likely to be effective. Nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs) have been a prime focus for developing once-daily therapies primarily because they form the backbone of most current regimens. Within the NRTI class, however, drugs differ in their pharmacokinetic properties, such as plasma and intracellular half-lives, and thus in their suitability for once-daily dosing. For example, newer NRTIs, such as tenofovir and emtricitabine, combine longer plasma half-lives with longer intracellular half-lives, prolonging exposure and the period of pharmacologic activity. Of equal importance, the clinical impact of systemic and intracellular interactions between concomitant drugs defines which once-daily drugs may be combined in once-daily regimens. To construct simplified and effective therapies for individual patients, clinicians require an understanding of the plasma and intracellular pharmacokinetic properties of NRTIs and how these properties determine a drug's appropriateness for once-daily dosing and placement within a once-daily regimen.

Once-daily antiretroviral therapy: Spanish Consensus Statement

BACKGROUND

Administration of antiretroviral therapy (ART) once daily is creating extraordinary interest among the members of the scientific community and also among those who receive the therapy. However, in clinical practice, some doubts remain about its use.

OBJECTIVES

This document examines the characteristics and possibilities of treatment administered once daily.

METHODS

Consensus of 248 Spanish experts in the field.

RESULTS

Once-daily dosing is considered an added value which could favour adherence and, therefore, efficacy, as well as the quality of life of certain patients, however, the objective of adequate adherence in the long term is often difficult to achieve regardless of the treatment used. In theory, any patient can receive once-daily therapy, although some patients could particularly benefit from it, e.g. those with unfavourable social or personal circumstances, including drug users, patients whose treatment must be supervised, patients receiving multiple medications, or those who need rescue therapy after multiple treatment failures. At present, it is possible to design once-daily ART using some of the combinations of drugs considered as first-choice in national and international recommendations for antiretroviral therapy, but the options are still limited. The marketing of new drugs with this characteristic could allow us to increase the number and types of patient who can benefit from once-daily regimens, including those patients who need rescue therapy.

CONCLUSIONS

Once-daily ART is a good alternative to regimens administered several times each day when a potent combination of active drugs is available.

Better maintained adherence on switching from twice-daily to once-daily therapy for HIV: a 24-week randomized trial of treatment simplification using stavudine prolonged-release capsules

BACKGROUND

Adherence to antiretroviral therapy is critical to treatment outcomes. Adherence studies in other therapeutic areas of medicine suggest that once-daily regimens support improved adherence when compared to twice-daily therapy. An expansion in the range of once-daily antiretrovirals is making once-daily therapy possible for persons with HIV infection.

METHODS

A 24-week randomized open-label simplification study of twice-daily regimens based on stavudine immediate release or zidovudine to an all once-daily regimen based on the stavudine prolonged-release capsule (PRC), in persons with complete virological suppression on regimens also including efavirenz and lamivudine, was carried out. Subjects were assessed for adherence [using the Medication Event Monitoring System (MEMS) cap; Aardex Corporation, Union City, CA, USA], quality of life, tolerability and efficacy.

RESULTS

Forty-three patients were randomly assigned: 21 remained on their original regimen and 22 switched to once-daily therapy with stavudine PRC. Although high levels of adherence and good quality of life were present at study enrollment, adherence declined to a significantly lesser extent at week 24 in the group that switched to once-daily therapy. Efficacy was maintained in both groups and there were no differences in tolerability or toxicity.

CONCLUSIONS

Subjects switching from twice-daily therapy to once-daily therapy demonstrate less of a decline in adherence over 24 weeks. A once-daily regimen including stavudine PRC is as effective and tolerable as a regimen containing the twice-daily formulation.

Plasma Pharmacokinetics of Once- versus Twice-Daily Lamivudine and Abacavir: Simplification of Combination Treatment in HIV-1-Infected Children (Penta-13)

Background

There are few data on plasma and intracellular pharmacokinetics (PK) of once-daily (q24h) nucleoside analogues in HIV-infected children.

Methods

Children aged 2–13 years receiving combination treatment containing lamivudine (3TC) (4 mg/kg) and/or abacavir (ABC) (8 mg/kg) twice daily (q12h) were included in this single-arm, open-label, crossover study. Intensive plasma PK sampling was performed at steady state, after which children switched to q24h dosing and PK sampling was repeated 4 weeks later. Daily area under the curve (AUC0–24) and peak level (Cmax) of q24h and q12h regimens were compared by geometric mean ratios (GMRs) with 90% confidence intervals (CIs). Children were followed for 24 weeks to evaluate safety and virological response.

Results

24 children were enrolled, of whom 20 [median age (range) 5.6 (2.1–12.8) years] had evaluable PK data for 3TC ( n=19) and/or ABC ( n=14). GMRs of 3TC and ABC AUC0–24 and Cmax q24h versus q12h significantly exceeded 1.0. GMRs were not significantly different between children aged 2–6 versus 6–13 years old ( P>0.08). Of note, 3TC Cmax values for both q12h and q24h were significantly lower in children aged 2–6 versus 6–13 years old. No child discontinued due to adverse events. At baseline, 16 out of 20 children had a viral load <100 copies/ml compared with 17 out of 19 at week 24.

Conclusion

AUC0–24 and Cmax of both 3TC and ABC q24h were not inferior to q12h dosing in children. Insufficient results were obtained concerning intracellular levels of the active triphosphate moieties of both agents. Virological data did not indicate a marked difference in antiviral activity between q12h and q24h regimens.

Pharmacologic Perspectives for Once-Daily Antiretroviral Therapy

OBJECTIVE

To contrast available once-daily antiretroviral agents and combinations of these agents from a clinical pharmacologic viewpoint.

DATA SOURCES

Data were extracted from publications and major HIV conference proceedings cited in MEDLINE (1966–March 2004) using the search terms antiretroviral therapy, combination therapy, once-daily therapy, and pharmacokinetics. Additional references were obtained from the bibliographies of these sources.

STUDY SELECTION AND DATA EXTRACTION

Information pertaining to pharmacologic perspectives for once-daily antiretroviral agents was selected.

DATA SYNTHESIS

Maximal and durable suppression of plasma HIV RNA, the principal goal of therapy, depends on the intrinsic antiviral activity of the antiretroviral regimen. A favorable tolerability/toxicity profile is also fundamentally important. All once-daily agents exhibit some pharmacologic limitations or lack adequate long-term follow-up. Of available agents, efavirenz has a long and distinguished efficacy record, with reasonable safety and moderate tolerability. Lamivudine, and newer agents such as atazanavir (or atazanavir/ritonavir), emtricitabine, fosamprenavir/ritonavir, and tenofovir, may offer pharmacologic advantages in the current state of once-daily therapy. Important considerations exist for coadministering once-daily agents including drug–drug interactions, drug–food incompatibilities, and synergistic toxicities. Few controlled studies have compared once-daily regimens with conventional regimens.

CONCLUSIONS

Progress has been made toward once-daily therapy, but more clinical experience with available agents is needed, including comparative studies of entirely once-daily regimens versus conventional regimens. Limitations of currently available agents signify a need for improved antiretroviral utilization or new alternative agents.

Once-daily versus twice-daily lamivudine, in combination with zidovudine and efavirenz, for the treatment of antiretroviral-naive adults with HIV infection: a randomized equivalence trial

A randomized, double-blind, double-dummy controlled, multicenter trial was conducted that involved 554 antiretroviral-naive human immunodeficiency virus-infected adults (plasma HIV type 1 [HIV-1] RNA level, >or=400 copies/mL; CD4(+) cell count, >100 cells/mm(3)) and compared a 300-mg once-daily (q.d.) regimen of lamivudine (3TC) versus a 150-mg twice-daily (b.i.d.) regimen of 3TC, combined with zidovudine (300 mg b.i.d.) and efavirenz (600 mg q.d.), during a 48-week period. Treatments were considered equivalent if the 95% confidence interval (CI) for the difference in proportions of patients achieving an HIV-1 RNA level of <400 copies/mL was within the bound of -12% to 12%. At week 48 of the study, an intent-to-treat analysis in which patients with missing data were considered to have experienced treatment failure showed that the 3TC q.d. and 3TC b.i.d. regimens were equivalent (HIV-1 RNA level <400 copies/mL, 178 [64%] of 278 vs. 174 [63%] of 276; treatment difference, 1% [95% CI, -7.1% to 8.9%]; HIV-1 RNA level <50 copies/mL, 165 [59%] of 278 vs. 168 [61%] of 276; treatment difference, 1.7% [95% CI, -9.7% to 6.6%]). Median increase above baseline in CD4(+) cell count was similar (q.d. group, +144 cells/mm(3); b.i.d. group, +146 cells/mm(3)), and the incidences of adverse events, disease progression, and HIV-associated conditions were comparable.

Failures of 1 week on, 1 week off antiretroviral therapies in a randomized trial

BACKGROUND

Scheduled treatment interruptions are being evaluated in an effort to decrease costs and side effects of highly active antiretroviral therapy (HAART). A schedule of 1 week on and 1 week off therapy offers the promise of 50% less drug exposure with continuously undetectable HIV RNA concentration.

METHODS

In the Staccato study 600 patients on successful HAART were to be randomized to either continued therapy, CD4-guided therapy, or one week on, one week off therapy. A scheduled preliminary analysis evaluated effectiveness in the 1-week-on-1-week-off arm.

RESULTS

Of 36 evaluable patients, 19 (53%) had two successive HIV RNA concentrations > 500 copies/ml at the end of the week off therapy, and were classified as virological failure. Most of those who failed took didanosine, stavudine, saquinavir, and ritonavir (11 patients). In these patients, there was no evidence of mutations suggestive of drug resistance, and plasma saquinavir levels were within the expected range. Two of three patients failing on triple nucleotides had drug resistance mutations, but nonetheless responded to reintroduction of triple nucleotide therapy. One of two patients taking nevirapine, and one of eight taking efavirenz, also failed. Both had resistance mutations at the time of failure, but not at baseline.

CONCLUSIONS

The 1-week-on-1-week-off schedule, as tested in the Staccato study, showed an unacceptably high failure rate and was therefore terminated.

Simplified regimens for treating HIV infection and AIDS

PURPOSE

To review the variables that greatly affect adherence to the complex treatment regimens used in HIV disease and to examine available options that could improve patient outcomes.

DATA SOURCES

Comprehensive review of current medical and scientific literature, drug-prescribing literature, and randomized clinical trials of drug treatments.

CONCLUSIONS

Effective treatment of HIV infection is dependent on consistent adherence to prescribed antiretroviral medications. A large pill burden, multiple daily doses, and adverse events are some of the complexities that negatively impact patient adherence. For example, lipodystrophy and hyperlipidemia are two serious side effects associated with some agents. Once-daily antiretroviral agents offer many advantages over historical treatment options but are associated with possible drawbacks.

IMPLICATIONS FOR PRACTICE

Currently, four single agents are available for once-daily administration, and a few others are under investigation. In addition, combination therapy with either dual or boosted protease inhibitor regimens is becoming a popular way of overcoming the poor pharmacokinetic characteristics of individual protease inhibitors.

Lamivudine can exert a modest antiviral effect against human immunodeficiency virus type 1 containing the M184V mutation

The M184V mutation in human immunodeficiency virus (HIV) reverse transcriptase is associated with high-level resistance to both (-)2',3'-dideoxy-3'-thiacytidine (3TC) and (-)2',3'-dideoxy-5-fluoro-3'-thiacytidine as well as low-level resistance to 2',3'-dideoxyinosine, 2',3'-dideoxycytidine, and abacavir. This mutation is also associated with diminished HIV replicative fitness as well as several functional changes in enzyme activity, including diminutions in polymerase processivity, pyrophosphorylysis, and nucleotide primer unblocking. Despite the fact that M184V encodes up to 1,000-fold resistance to 3TC, we asked whether this drug might still display some antiviral effect in regard to viruses containing this mutation. Cell-free assays revealed that high concentrations of 3TC triphosphate (i.e., >100 micro M) could affect chain termination and/or inhibit purified reverse transcriptase containing the M184V substitution. This effect became more pronounced with elongation of reverse transcriptase products. In newly infected cells (i.e., peripheral blood mononuclear cells), we found that the amount of full-length reverse transcriptase product was diminished in the presence of 2 to 10 micro M 3TC, although no decrease in the first product of the reverse transcriptase reaction, i.e., minus strong-stop DNA, was observed. In the presence of two other HIV inhibitors, e.g., nevirapine and indinavir, 3TC exerted additive effects in tissue culture at concentrations only marginally higher than the 50% inhibitory concentration (IC(50)). Reverse transcriptases cloned from clinical isolates harboring M184V in the context of multidrug resistance had similar IC(50) values for 3TC triphosphate compared to reverse transcriptase containing only the M184V mutation. These results suggest that viruses containing M184V can retain a higher degree of sensitivity to 3TC than previously assumed.

Once-Daily Administration of Antiretrovirals

Adherence to therapy is of critical importance for the long-term success of the treatment of HIV infection. Once-daily administration of antiretroviral agents is appealing, as it may increase patient's adherence. The pharmaceutical industry is making huge efforts to develop drugs or combinations of drugs with pharmacokinetic properties allowing once-daily administration. The major pharmacokinetic requirement for once-daily administration is that the intracellular concentration of the antiretroviral or its active metabolite remains above the minimal concentration that can inhibit viral replication during the entire 24-hour period. Soon, all three major classes of antiretroviral agents will be available as once-daily formulations. However, only a few clinical trials have yet assessed the efficacy and safety of truly once-daily antiretroviral combinations. Preliminary results from these small pilot studies suggest that once-daily administration of antiretrovirals is a feasible approach. Large comparative trials are needed before the real benefits of such a strategy can be fully assessed.