Antiviral effect and pharmacokinetic interaction between nevirapine and indinavir in persons infected with human immunodeficiency virus type 1

A Literature Review of Liver Function Test Elevations in Rifampin Drug-Drug Interaction Studies

Although rifampin drug–drug interaction (DDI) studies are routinely conducted, there have been instances of liver function test (LFT) elevations, warranting further evaluation. A literature review was conducted to identify studies in which combination with rifampin resulted in hepatic events and evaluate any similarities. Over 600 abstracts and manuscripts describing rifampin DDI studies were first evaluated, of which 30 clinical studies reported LFT elevations. Out of these, 11 studies included ritonavir in combination with other drug(s) in the rifampin DDI study. The number of subjects that were discontinued from treatment on these studies ranged from 0 to 71 (0–100% of subjects in each study). The number of subjects hospitalized for adverse events in these studies ranged from 0 to 41 (0–83.67% of subjects in each study). LFT elevations in greater than 50% of subjects were noted during the concomitant administration of rifampin with ritonavir‐boosted protease inhibitors and with lorlatinib; with labeled contraindication due to observed hepatotoxicity related safety findings only for saquinavir/ritonavir and lorlatinib. In the lorlatinib and ritonavir DDI studies, considerable LFT elevations were observed rapidly, typically within 24–72 h following co‐administration. A possible sequence effect has been speculated, where rifampin induction prior to administration of the combination may be associated with increased severity of the LFT elevations. The potential role of rifampin in the metabolic activation of certain drugs into metabolites with hepatic effects needs to be taken into consideration when conducting rifampin DDI studies, particularly those for which the metabolic profiles are not fully elucidated.

Designing Out PXR Activity on Drug Discovery Projects: A Review of Structure-Based Methods, Empirical and Computational Approaches

This perspective discusses the role of pregnane xenobiotic receptor (PXR) in drug discovery and the impact of its activation on CYP3A4 induction. The use of structural biology to reduce PXR activity on drug discovery projects has become more common in recent years. Analysis of this work highlights several important molecular interactions, and the resultant structural modifications to reduce PXR activity are summarized. The computational approaches undertaken to support the design of new drugs devoid of PXR activation potential are also discussed. Finally, the SAR of empirical design strategies to reduce PXR activity is reviewed, and the key SAR transformations are discussed and summarized. In conclusion, this perspective demonstrates that PXR activity can be greatly diminished or negated on active drug discovery projects with the knowledge now available. This perspective should be useful to anyone who seeks to reduce PXR activity on a drug discovery project.

Clinical Utility of Current NNRTIs and Perspectives of New Agents in This Class under Development

Highly active antiretroviral therapy (HAART) has significantly reduced the number of deaths caused by AIDS. However, the antiviral efficacy of HAART comprising protease inhibitors (PIs) and nucleoside reverse transcriptase inhibitors (NRTIs) is frequently accompanied by a decrease in patients' quality of life. PI-based therapies often fail due to poor adherence caused by heavy pill burden, complex dosing schedules and undesirable side effects. The current trend is to switch from PI-based to PI-sparing regimens consisting of non-nucleoside reverse transcriptase inhibitors (NNRTIs) and NRTIs. Despite some encouraging results from NNRTI-containing therapies, two major concerns in using the currently available NNRTIs remain: 1) low genetic barrier to the emergence of resistance and 2) cross-resistance due to single mutations that often render the whole class of NNRTIs ineffective. Clearly, new and improved NNRTIs are needed to address these concerns.

Differences in the Prediction of Area Under the Curve for a Protease Inhibitor Using Trough Versus Peak Concentration: Assessment Using Published Pharmacokinetic Data for Indinavir

In the present day antiretroviral therapy, Ctrough is a key tool for efficacy assessment. The present work explored the feasibility of using Ctrough or Cmax in the area under the concentration-time curve (AUC) prediction of indinavir. A simple unweighted linear regression model was developed to describe the relationship between Cmax versus AUC (r = 0.8101, P < 0.001) and Ctrough versus AUC (r = 0.8127, P < 0.001) for indinavir. The regression lines were used to predict the AUC values from literature Cmax or Ctrough data of indinavir in HIV and healthy subjects. The fold difference, defined as the quotient of the observed and predicted AUC values, was evaluated along with statistical comparison, including root mean square error (RMSE) prediction for the 2 models. The correlation between Cmax versus AUC and Ctrough versus AUC was established. Majority of the predicted values for Cmax versus AUC were within 0.75- to 1.5-fold differences. However, the Ctrough versus AUC model showed larger variability with approximately one-third of the predictions within 0.75- to 1.5-fold differences. The r value and %RMSE for observed versus predicted AUC for Ctrough (r = 0.5925, n = 65, P < 0.001, and RMSE: 67%) were inferior to the Cmax (r = 0.8773, n = 86, P < 0.001, and RMSE: 46%). In conclusion, Cmax versus AUC and Ctrough versus AUC relationships were established for indinavir showing the utility of a single concentration time point for therapeutic drug monitoring purpose. The Cmax model for indinavir may be more relevant for AUC prediction as determined by the statistical criteria.

Nevirapine in the treatment of HIV

Nevirapine (Viramune, Boehringer Ingelheim Ltd) is the first marketed non-nucleoside reverse transcriptase inhibitor. As with any antiretroviral drug, nevirapine should always be used as part of a fully suppressive regimen. Clinical studies have shown that nevirapine-containing regimens may accomplish durable virological and immunological responses in approximately half of all antiretroviral-naive patients. It can also be successfully used as a component of salvage therapies and as a part of a strategy to simplify protease inhibitor-containing regimens. Nevirapine has a beneficial effect on the lipid profile in both treatment-naive and -experienced patients. Nevirapine also has an important role in preventing mother-to-child transmission of HIV. It is usually well-tolerated with rash and liver toxicity being the most frequently reported adverse events. Nevirapine interacts with cytochrome P450 enzymes both as a substrate and as an inducer. For this reason, therapeutic drug monitoring should be recommended whenever nevirapine is used with protease inhibitors, methadone (Methadose, Rosemont Pharmaceuticals Ltd), oral contraceptives, rifampicin (Rifadin, Aventis Pharma) and other potentially interacting drugs. Nevirapine-resistant mutations are common to the non-nucleoside reverse transcriptase inhibitor family and they include K103N, V106A, Y181C, Y188C and G190A. A better understanding of the nevirapine profile will certainly contribute to ensuring that its clinical application becomes more effective and beneficial.

A review of pharmacological interactions between HIV or hepatitis C virus medications and opioid agonist therapy: implications and management for clinical practice

Global access to opioid agonist therapy and HIV/hepatitis C virus (HCV) treatment is expanding but when used concurrently, problematic pharmacokinetic and pharmacodynamic interactions may occur. Articles published from 1966 to 2012 in Medline were reviewed using the following keywords: HIV, AIDS, HIV therapy, HCV, HCV therapy, antiretroviral therapy, highly active antiretroviral therapy, drug interactions, methadone and buprenorphine. In addition, a review of abstracts from national and international meetings and conference proceedings was conducted; selected reports were reviewed as well. The metabolism of both opioid and antiretroviral therapies, description of their known interactions and clinical implications and management of these interactions were reviewed. Important pharmacokinetic and pharmacodynamic drug interactions affecting either methadone or HIV medications have been demonstrated within each class of antiretroviral agents. Drug interactions between methadone, buprenorphine and HIV medications are known and may have important clinical consequences. Clinicians must be alert to these interactions and have a basic knowledge regarding their management.

Plasma concentrations of efavirenz and nevirapine among HIV-infected patients with immunological failure attending a tertiary hospital in North-western Tanzania

BACKGROUND

Sub-therapeutic and supra-therapeutic plasma concentrations of antriretrovirals are the significant causes of treatment failure and toxicity respectively among HIV-infected patients. We conducted this study to determine the pattern of efavirenz and nevirapine plasma drug concentrations among adult HIV-infected patients with immunological failure attending at a tertiary hospital in North-western Tanzania.

MATERIALS AND METHODS

A cross-sectional study was conducted among adult HIV-infected patients with immunological failure who have been on either efavirenz or nevirapine based antiretroviral regimen for more than 6 months. Patients were serially enrolled through routine Care and Treatment Clinic (CTC) activities. Plasma drug concentrations for efavirenz and nevirapine were determined by high performance liquid chromatography (HPLC) and Gas Chromatography (GC) respectively. Demographic, clinical and laboratory data such as viral load and CD4 counts were collected. Data analysis was done using STATA 12.

RESULTS

Of the 152 patients with immunological failure enrolled, the sub-therapeutic, therapeutic and supra-therapeutic plasma antiretroviral drug concentrations were found in 43/152 (28.3%), 76/152 (50.0%) and 33/152 (21.7%) respectively. Half of the patients were outside therapeutic window with either sub-therapeutic or supra-therapeutic plasma ARV drug concentrations. There was a significant difference in distribution of ARV adherence (p-value<0.001), NRTI backbone (p-value = 0.039), HIV stage (p-value = 0.026) and viral load (p-value = 0.007) within sub-therapeutic, therapeutic and supra-therapeutic ARV plasma drug concentrations.

CONCLUSION

There is a wide inter-individual variability of plasma ARV concentrations among HIV patients with immunological failure, with a large proportion of patients being outside therapeutic window. This variability is significant based on ARV adherence, NRTI backbone, viral load and HIV stage. Routine therapeutic drug monitoring (TDM) could assist identifying these patients early and making timely correction to avoid virological failure, poor immunological outcome and prevent associated drug toxicities. Nonetheless, ARV adherence should be strictly emphasized on HIV patients with immunological failure.

Integration of data from multiple sources for simultaneous modelling analysis: experience from nevirapine population pharmacokinetics

AIMS

To propose a modelling strategy to efficiently integrate data from different sources in one simultaneous analysis, using nevirapine population pharmacokinetic data as an example.

METHODS

Data from three studies including 115 human immunodeficiency virus-infected South African adults were used. Patients were on antiretroviral therapy regimens including 200 mg nevirapine twice daily and sampled at steady state. A development process was suggested, implemented in NONMEM7 and the final model evaluated with an external data set.

RESULTS

A stepwise approach proved efficient. Model development started with the intensively sampled data. Data were added sequentially, using visual predictive checks for inspecting their compatibility with the existing model. Covariate exploration was carried out, and auxiliary regression models were designed for imputation of missing covariates. Nevirapine pharmacokinetics was described by a one-compartment model with absorption through two transit compartments. Body size was accounted for using allometric scaling. The model included a mixture of two subpopulations with different typical values of clearance, namely fast (3.12 l h(-1)) and slow metabolizers (1.45 l h(-1)), with 17% probability of belonging to the latter. Absorption displayed large between-occasion variability, and food slowed the absorption mean transit time from 0.6 to 2.5 h. Concomitant antitubercular treatment including rifampicin typically decreased bioavailability by 39%, with significant between-subject variability. Visual predictive checks of external validation data indicated good predictive performance.

CONCLUSIONS

The development strategy succeeded in integrating data from different sources to produce a model with robust parameter estimates. This work paves the way for the creation of a nevirapine mega-model, including additional data from numerous diverse sources.

Drug Interaction of Fluvoxamine and Fluoxetine with Nevirapine in HIV-1-Infected Individuals

OBJECTIVE

To evaluate the possible pharmacokinetic interactions between nevirapine and fluvoxamine or fluoxetine in patients with HIV-1 infection.

PATIENTS AND METHODS

Patients who were using fluvoxamine or fluoxetine concomitantly were chosen from an unselected cohort (n = 173) of HIV-1-infected individuals using a nevirapine-containing regimen (study group). HIV-1-infected patients using nevirapine without fluvoxamine or fluoxetine and non-HIV-infected individuals who were using fluvoxamine and fluoxetine were included as controls. The influence of fluvoxamine and fluoxetine on the pharmacokinetics of nevirapine was investigated with a previously developed population pharmacokinetic model. Concomitant use of fluvoxamine or fluoxetine was tested independently as covariate for apparent clearance (CL/F) of nevirapine using nonlinear mixed-effect modelling (NONMEM). Furthermore, to explore the influence of nevirapine on the pharmacokinetics of fluvoxamine and fluoxetine, dose-normalised concentrations of fluvoxamine and fluoxetine from the study group were compared with those of the controls.

RESULTS

Of the 173 HIV-1-infected individuals, 14 were using fluoxetine (n = 7) or fluvoxamine (n = 7) simultaneously with nevirapine. In addition, 17 and 29 individuals were identified as controls for the fluoxetine- and fluvoxamine-group, respectively. Concomitant use of fluvoxamine resulted in a significant reduction of 33.7% in CL/F of nevirapine; this reduction in CL/F appeared to be dose-dependent. Concomitant use of fluoxetine had no influence on the pharmacokinetics of nevirapine. Conversely, nevirapine significantly lowered plasma levels of fluoxetine plus norfluoxetine (seproxetine). In contrast, no significant difference was observed in dose-normalised concentrations of fluvoxamine when the controls were compared with the study group.

CONCLUSION

We advise that special attention is paid to HIV-1-infected indivi-duals using a nevirapine-containing regimen and fluvoxamine or fluoxetine con-comitantly, since pharmacokinetic interactions have been observed.

Molecular mechanisms of drug transporter regulation

Interindividual differences in drug transporter expression can result in variability in drug response. This variation in gene expression is determined, in part, by the actions of nuclear hormone receptors that act as xenobiotic- and endobiotic-sensing transcription factors. Among the ligand-activated nuclear receptors, signaling through the pregnane X receptor (PXR), constitutive androstane receptor (CAR), farnesoid X receptor (FXR), and vitamin D receptor (VDR) constitute major pathways regulating drug transporter expression in tissues. Hence, these endobiotic- and xenobiotic-sensing nuclear receptors are intrinsically involved in environmental influences of drug response. Moreover, because nuclear receptor genes are polymorphic, these transcription factors are also thought to contribute to heritability of variable drug action. In this chapter, the molecular aspects of drug transporter gene regulation by ligand-activated nuclear receptors will be reviewed including their clinical relevance.

CYP2C19 genetic variants affect nelfinavir pharmacokinetics and virologic response in HIV-1-infected children receiving highly active antiretroviral therapy

BACKGROUND

The objective of this research was to identify the impact of genetic variants of P-glycoprotein (ABCB1) and cytochrome P450 (CYP) on nelfinavir pharmacokinetics and response to highly active antiretroviral therapy (HAART) in HIV-1-infected children.

METHODS

HIV-1-infected children (n = 152) from Pediatric AIDS Clinical Trial Group 366 or 377 receiving nelfinavir as a component of HAART were evaluated. Genomic DNA was assayed for ABCB1 and CYP genetic variants using real-time polymerase chain reaction Nelfinavir oral clearance (CL/F), M8 to nelfinavir ratios, CD4 T cells, and HIV-1-RNA were measured during HAART.

RESULTS

Nelfinavir CL/F and M8 to nelfinavir ratios were significantly associated with the CYP2C19-G681A genotypes (P < 0.001). Furthermore, the CYP2C19-G681A genotype was related to virologic responses at week 24 (P = 0.01). A multivariate analysis demonstrated that age (P = 0.03), concomitant protease inhibitor use (P < 0.001), and the CYP2C19-G681A genotype (P < 0.001) remained significant covariates associated with nelfinavir CL/F.

CONCLUSIONS

CYP2C19 genotypes altered nelfinavir pharmacokinetics and the virologic response to HAART in HIV-1-infected children. These findings suggest that CYP2C19 genotypes are important determinants of nelfinavir pharmacokinetics and virologic response in HIV-1-infected children.

Polymorphism of human cytochrome P450 enzymes and its clinical impact

Pharmacogenetics is the study of how interindividual variations in the DNA sequence of specific genes affect drug response. This article highlights current pharmacogenetic knowledge on important human drug-metabolizing cytochrome P450s (CYPs) to understand the large interindividual variability in drug clearance and responses in clinical practice. The human CYP superfamily contains 57 functional genes and 58 pseudogenes, with members of the 1, 2, and 3 families playing an important role in the metabolism of therapeutic drugs, other xenobiotics, and some endogenous compounds. Polymorphisms in the CYP family may have had the most impact on the fate of therapeutic drugs. CYP2D6, 2C19, and 2C9 polymorphisms account for the most frequent variations in phase I metabolism of drugs, since almost 80% of drugs in use today are metabolized by these enzymes. Approximately 5-14% of Caucasians, 0-5% Africans, and 0-1% of Asians lack CYP2D6 activity, and these individuals are known as poor metabolizers. CYP2C9 is another clinically significant enzyme that demonstrates multiple genetic variants with a potentially functional impact on the efficacy and adverse effects of drugs that are mainly eliminated by this enzyme. Studies into the CYP2C9 polymorphism have highlighted the importance of the CYP2C9*2 and *3 alleles. Extensive polymorphism also occurs in other CYP genes, such as CYP1A1, 2A6, 2A13, 2C8, 3A4, and 3A5. Since several of these CYPs (e.g., CYP1A1 and 1A2) play a role in the bioactivation of many procarcinogens, polymorphisms of these enzymes may contribute to the variable susceptibility to carcinogenesis. The distribution of the common variant alleles of CYP genes varies among different ethnic populations. Pharmacogenetics has the potential to achieve optimal quality use of medicines, and to improve the efficacy and safety of both prospective and currently available drugs. Further studies are warranted to explore the gene-dose, gene-concentration, and gene-response relationships for these important drug-metabolizing CYPs.

Effectiveness and metabolic complications after 96 weeks of a generic fixed-dose combination of stavudine, lamivudine, and nevirapine among antiretroviral-naive advanced HIV-infected patients in Thailand: A prospective study

BACKGROUND

Generic fixed-dose combination (FDC) antiretroviral therapy (ART) has been widely used in resource-limited settings. Treatment based on these combinations provide low pill burden and are less expensive.

OBJECTIVE

The aim of this study was to determine the long-term effectiveness and metabolic complications of a generic FDC of stavudine (d4T)/lamivudine (3TC)/ nevirapine (NVP), among ART-naive HIV-infected patients.

METHODS

A prospective study was conducted among patients who were initiated on d4T/3TC/NVP between November 2004 and March 2005. Plasma HIV-1 RNA, CD4 and alanine transaminase were assessed every 12 weeks. Fasting plasma glucose (FPG) and lipid profile were determined at 96 weeks. Adverse events and genotypic drug resistance were recorded. The primary outcome of interest was the proportion of patients who achieved plasma HIV-1 RNA <50 copies/mL after 96 weeks of ART and analyzed by intent-to-treat (ITT) and on-treatment (OT) populations.

RESULTS

There were 140 patients (mean [SD] age, 35.7 [7.6] years; male, 67.9%) enrolled in the study. Median (interquartile range [IQR]) baseline CD4 was 31 (14-79) cells/mm(3) and HIV-1 RNA count was 433,500 (169,000-750,000) copies/mL. At week 96, 87 patients (ITT, 62.1%; OT, 87.0%) achieved HIV-1 RNA -50 copies/mL. Median (IQR) CD4 at 96 weeks was 328 (229-450) cells/mm(3). The reasons for drug discontinuation were as follows: drug resistance (9.3%), lost to follow-up (9.3%), NVP- related rashes (7.9%), death (5.0%), d4T-related adverse events (3.6%), and transferred to another hospital (2.1%). At 96 weeks, 25 patients (28.7%) had low-density lipoprotein cholesterol (LDL-C) >130 mg/dL, 7 (8.0%) had LDL-C >160 mg/dL, 6 (6.9%) had triglycerides >400 mg/dL, and 2 (2.3%) had FPG >126 mg/dL. Eleven patients (12.6%) had a lactic acid level >2.5 mmol/L. Eight patients (9.2%) needed to take antihypertensive agents. Of 13 patients who developed virologic failure, 76.9% and 61.5% had M184V/I and Y181C/I mutations, respectively.

CONCLUSIONS

Initiation of this FDC ofd4T/3TC/NVP in these ART-naive patients with advanced HIV infection and low baseline CD4 cell count was effective at 96 weeks of follow-up with regard to virologic and immunologic responses. However, long-term metabolic complications, particularly dyslipidemia, were common and should be closely monitored.

Drug-Sparing Regimens for HIV Combination Therapy: Benefits Predicted for “Drug Coasting”

Structured Treatment Interruptions (STI) during HIV drug therapy were thought to potentially reduce side effects and toxicity, boost immune involvement, and possibly lower the viral set-point. Clinical trials of STI regimens, however, have had mixed results. We use an established mathematical model of HAART to estimate possible therapeutic outcomes for STI and for other, similar patterns in HIV combination therapy. We perform an exhaustive search of patterns of up to 60 days, for triple-drug combinations involving accurate pharmacokinetics for 12 specific antiviral drugs. The results of this analysis are consistent with recent clinical trials which have demonstrated that STI-type patterns, involving therapy interruption of weeks or months, are rarely optimal. Our analysis predicts, however, that the benefit of treatment can often be improved by including very short drug-free periods, during which the patient effectively "coasts" for a day or two on adequate drug concentrations due to the long half-life of some pharmaceuticals. Our analysis predicts many cases in which this may be achieved without increasing the risk of drug-resistance. This suggests that "drug coasting" patterns, significantly shorter than STI patterns, may merit further clinical investigation in efforts to find drug-sparing regimens for HIV.

Indinavir Trough Concentration as a Determinant of Early Nephrolithiasis in HIV-1-Infected Adults

Indinavir plasma levels are associated with antiretroviral efficacy; however, little data are available regarding toxicity. We assessed the relationship between indinavir pharmacokinetic (PK) characteristics and severe nephrolithiasis as well as other severe or serious adverse reactions. Patients included in the ANRS CO8 APROCO-COPILOTE cohort and receiving 800 mg indinavir three times daily as a first-line protease inhibitor were eligible for this study. To be included in the analysis, their plasma sample at month 1 (M1) had to be available (n = 282) to estimate using population PK modeling, indinavir PK characteristics, ie, maximum (Cmax) and trough plasma (Cres) concentrations, area under the curve (AUC), and observed/predicted concentration ratio (CR). A Cox model was used to estimate the independent effect of Cmax, Cres, AUC, and CR on the hazard of severe nephrolithiasis and serious adverse reactions. At M1, median Cmax was 6205 ng/mL, Cres 631 ng/mL, AUC 24,242 ng . h/mL, and CR 0.6. After a median follow up of 12 months, 11% of patients (30 of 282) had experienced at least one serious adverse reaction among which 12 were nephrolithiasis. In the multivariate analyses, early high indinavir Cres (ie, >/=1000 ng/mL at M1) was associated with a higher rate of severe nephrolithiasis (hazard ratio = 6.7; 95% confidence interval = 1.8-25.2; P < 0.01) and was also associated with a higher rate of all serious adverse reactions but only when nephrolithiasis were included among those cases. Prospective and early indinavir Cres determination should be recommended in the patient's care management and dosage adjustments.

Safety and efficacy of a generic fixed-dose combination of stavudine, lamivudine and nevirapine antiretroviral therapy between HIV-infected patients with baseline CD4 <50 versus CD4 > or = 50 cells/mm3

Background

Antiretroviral therapy (ART) with a generic fixed-dose combination (FDC) of stavudine (d4T)/lamivudine (3TC)/nevirapine (NVP) is widely used in developing countries. The clinical data of this FDC among very advanced HIV-infected patients is limited.

Methods

A retrospective cohort study was conducted among ART-naïve HIV-infected patients who were initiated a generic FDC of d4T/3TC/NVP between May 2004 and October 2005. Patients were categorized into 2 groups according to the baseline CD4 (group A: <50 cell/mm³ and group B: ≥ 50 cell/mm³).

Results

There were 204 patients with a mean ± SD age of 37.1 ± 8.9 years, 120 (58.8%) in group A and 84 (41.2%) in group B. Median (IQR) CD4 cell count was 6 (16–29) cells/mm³ in group A and 139 (92–198) cells/mm³ in group B. Intention-to-treat analysis at 48 weeks, 71.7% (86/120) of group A and 75.0% (63/84) of group B achieved plasma HIV RNA <50 copies/ml (P = 0.633). On-treatment analysis, 90.5% (87/96) in group A and 96.9% (63/65) in group B achieved plasma HIV RNA <50 copies/ml (P = 0.206). At 12, 24, 36 and 48 weeks of ART, mean CD4 were 98, 142, 176 and 201 cells/mm³ in group A and 247, 301, 336 and 367 cells/mm³ in group B, respectively. There were no differences of probabilities to achieve HIV RNA <50 copies/ml (P = 0.947) and CD4 increment at 48 weeks between the two groups (P = 0.870). Seven (9.6%) patients in group A and 4 (8.5%) patients in group B developed skin reactions grade II or III (P = 1.000). ALT at 12 weeks was not different from that at baseline in both groups (P > 0.05).

Conclusion

Initiation of FDC of d4T/3TC/NVP in HIV-infected patients with CD4 <50 and ≥ 50 cells/mm³ has no different outcomes in terms of safety and efficacy. FDC of d4T/3TC/NVP can be effectively used in advance HIV-infected patients with CD4 <50 cells/mm³.

Costs versus benefits: best possible and best practical treatment regimens for HIV

Current HIV therapy, although highly effective, may cause very serious side effects, making adherence to the prescribed regimen difficult. Mathematical modeling may be used to evaluate alternative treatment regimens by weighing the positive results of treatment, such as higher levels of helper T cells, against the negative consequences, such as side effects and the possibility of resistance mutations. Although estimating the weights assigned to these factors is difficult, current clinical practice offers insight by defining situations in which therapy is considered "worthwhile". We therefore use clinical practice, along with the probability that a drug-resistant mutation is present at the start of therapy, to suggest methods of rationally estimating these weights. In our underlying model, we use ordinary differential equations to describe the time course of in-host HIV infection, and include populations of both activated CD4(+) T cells and CD8(+) T cells. We then determine the best possible treatment regimen, assuming that the effectiveness of the drug can be continually adjusted, and the best practical treatment regimen, evaluating all patterns of a block of days "on" therapy followed by a block of days "off" therapy. We find that when the tolerance for drug-resistant mutations is low, high drug concentrations which maintain low infected cell populations are optimal. In contrast, if the tolerance for drug-resistant mutations is fairly high, the optimal treatment involves periods of reduced drug exposure which consequently boost the immune response through increased antigen exposure. We elucidate the dependence of the optimal treatment regimen on the pharmacokinetic parameters of specific antiviral agents.

Incidence and risk factors of rash associated with efavirenz in HIV-infected patients with preceding nevirapine-associated rash

OBJECTIVE

To determine the incidence and risk factors of rash associated with efavirenz in HIV-infected patients with preceding nevirapine-associated rash.

METHODS

A retrospective cohort study was conducted in HIV-infected patients diagnosed with nevirapine-associated rash who subsequently received efavirenz between July 2003 and January 2005. Patients were followed up for 3 months after receiving efavirenz. Possible risk factors, including demographics, previous opportunistic infections, CD4 cell count, viral load, severity of nevirapine-associated rash and concurrent drugs, were studied and compared between those who had (group A) and did not have (group B) rash associated with efavirenz.

RESULTS

A total of 122 patients (52.5% male) were included in the study, with a mean age of 38.2 years. Median (and interquartile range) CD4 cell count and viral load were 55 (20-167) cells/microL and 86,150 (35,321-700,750) HIV-1 RNA copies/mL, respectively. Of the 122 patients, 10 (8.2%) developed rash associated with efavirenz and all required discontinuation of efavirenz. The baseline characteristics of group A (10 patients) and group B (112 patients) were similar. Median (and interquartile range) time from nevirapine discontinuation to efavirenz initiation was 12 (9-21) days in group A and 11 (7-21) days in group B (P=0.765). None of the risk factors investigated was associated with developing rash associated with efavirenz. The preceding development of severe nevirapine-associated rash had a trend towards a higher rate in group A than in group B (20.0% vs 10.7%; odds ratio=2.08; 95% confidence interval 0.39-10.97; P=0.322).

CONCLUSIONS

The majority (>90%) of HIV-infected patients with CD4 counts <200 cells/muL who had preceding nevirapine-associated rash could tolerate efavirenz well. Efavirenz may be an option for subsequent use in these patients, particularly in those who had preceding nevirapine-associated rash.

Population pharmacokinetics of indinavir alone and in combination with ritonavir in HIV-1-infected patients

AIMS

The aim of the study was to characterize the population pharmacokinetics of indinavir, define the relationship between the pharmacokinetics of indinavir and ritonavir, and to identify the factors influencing the pharmacokinetics of indinavir alone or when given with ritonavir.

METHODS

HIV-1-infected patients being treated with an indinavir-containing regimen were included. During regular visits, 102 blood samples were collected for the determination of plasma indinavir and ritonavir concentrations. Full pharmacokinetic curves were available from 45 patients. Concentrations of indinavir and ritonavir were determined by liquid chromatography coupled with electrospray tandem mass spectrometry. Pharmacokinetic analysis was performed using nonlinear mixed effect modelling (NONMEM).

RESULTS

The disposition of indinavir was best described by a single compartment model with first order absorption and elimination. Values for the clearance, volume of distribution and the absorption rate constant were 46.8 l h(-1) (24.2% IIV), 82.3 l (24.6% IIV) and 02.62 h(-1), respectively. An absorption lag-time of 0.485 h was detected in patients also taking ritonavir. Furthermore this drug, independent of dose (100-400 mg) or plasma concentration, decreased the clearance of indinavir by 64.6%. In contrast, co-administration of efavirenz or nevirapine increased the clearance of indinavir by 41%, irrespective of the presence or absence of ritonavir. Female patients had a 48% higher apparent bioavailability of indinavir than males.

CONCLUSIONS

The pharmacokinetic parameters of indinavir were adequately described by our population model. Female gender and concomitant use of ritonavir and non-nucleoside reverse transcriptase inhibitors strongly influenced the pharmacokinetics of this drug. The results support the concept of ritonavir boosting, maximum inhibition of indinavir metabolized being observed at 100 mg.

Pharmacokinetics of nevirapine in HIV-infected children receiving an adult fixed-dose combination of stavudine, lamivudine and nevirapine

OBJECTIVE

To evaluate the steady state pharmacokinetics of nevirapine (NVP) in HIV-infected children receiving a fixed-dose combination of stavudine, lamivudine and NVP.

METHODS

This cross-sectional study enrolled 34 children (18 girls) who had received GPO-VIR S30 (30 mg stavudine, 150 mg lamivudine and 200 mg NVP) for at least 8 weeks. Tablets were divided into quarter fractions (1/4, 1/2, 3/4 or 1 tablet) to attain the NVP dosages of 120-200 mg/m every 12 h. Plasma NVP levels were measured at predose, and at 2 and 6 h after drug administration.

RESULTS

The median age was 8.4 years (range, 3-15). Median CD4 lymphocyte count and percentage at study entry was 576 x 10 cells/l and 20.25%, respectively. The median pharmacokinetics parameters were area under the curve at 12 h, 78.4 h x mug/ml; minimum plasma drug concentration, 5.98 microg/ml; plasma half-life, 25.5 h; apparent oral clearance, 0.079 l/kg per h; and volume of distribution, 2.95 l/kg. Only one child had a minimum plasma drug concentration < 3.4 microg/ml (2.57 microg/ml). Of the 13 children who received GPO-VIR as their first-line regimen, 12 had plasma HIV-1 RNA < 400 copies/ml at 6-18 months, with a median CD4 lymphocyte increase of 216 and 433 x 10 cells/l at 6 and 12 months of treatment, respectively.

CONCLUSIONS

The administration of GPO-VIR S30 fixed-dose combination tablets in fractions or as a whole tablet to children resulted in appropriate NVP exposure and satisfactory virological and immunological benefit. This finding confirms the effectiveness of using a fixed-dose combination as a "transitional option" while waiting for a paediatric fixed-dose combination drug formulation.

Indinavir alters regulators of protein anabolism and catabolism in skeletal muscle

The HIV protease inhibitor indinavir adversely impairs carbohydrate and lipid metabolism, whereas its influence on protein metabolism under in vivo conditions remains unknown. The present study tested the hypothesis that indinavir also decreases basal protein synthesis and impairs the anabolic response to insulin in skeletal muscle. Indinavir was infused intravenously for 4 h into conscious rats, at which time the homeostasis model assessment of insulin resistance was increased. Indinavir decreased muscle protein synthesis by 30%, and this reduction was due to impaired translational efficiency. To identify potential mechanisms responsible for regulating mRNA translation, several eukaryotic initiation factors (eIFs) were examined. Under basal fasted conditions, there was a redistribution of eIF4E from the active eIF4E.eIF4G complex to the inactive eIF4E.4E-BP1 complex, and this change was associated with a marked decrease in the phosphorylation of 4E-BP1 in muscle. Likewise, indinavir decreased constitutive phosphorylation of eIF4G and mTOR in muscle, but not S6K1 or the ribosomal protein S6. In contrast, the ability of a maximally stimulating dose of insulin to increase the phosphorylation of PKB, 4E-BP1, S6K1, or mTOR was not altered 20 min after intravenous injection. Indinavir increased mRNA expression of the ubiquitin ligase MuRF1, but the plasma concentration of 3-methylhistidine remained unaltered. These indinavir-induced changes were associated with a marked reduction in the plasma testosterone concentration but were independent of changes in plasma levels of IGF-I, corticosterone, TNF-alpha, or IL-6. In conclusion, indinavir acutely impairs basal protein synthesis and translation initiation in skeletal muscle but, in contrast to muscle glucose uptake, does not impair insulin-stimulated signaling of protein synthetic pathways.

Management of HIV Infection in Persons Co-infected With Hepatitis

Co-infection with hepatitis C virus (HCV) and/or hepatitis B virus (HBV) is becoming a rampant disparity in HIV-infected patients. The advent of antiretroviral therapy has led to agents that are effective for suppression of both HIV and HBV; however, this can not be extrapolated to patients who are coinfected with HCV. Treatment of HCV disease is often strenuous and can lead to untoward adverse effects. Co-infection with HIV often leads to higher rates of cirrhosis and liver failure in patients with HBV or HCV, compromising antiretroviral treatment in this patient population due to the hepatotoxicity of these agents. The purpose of this review is to familiarize health care providers to the management of HIV infection in patients who are also co-infected with HBV or HCV.

Practical guidelines to interpret plasma concentrations of antiretroviral drugs

Several relationships have been reported between antiretroviral drug concentrations and the efficacy of treatment, and toxicity. Therefore, therapeutic drug monitoring (TDM) may be a valuable tool in improving the treatment of HIV-1-infected patients in daily practice. In this regard, several measures of exposure have been studied, e.g. trough and maximum concentrations, concentration ratios and the inhibitory quotient. However, it has not been unambiguously established which pharmacokinetic parameter should be monitored to maintain optimal viral suppression. Each pharmacokinetic parameter has its pros and cons. Many factors can affect the pharmacokinetics of antiretroviral agents, resulting in variability in plasma concentrations between and within patients. Therefore, plasma concentrations should be considered on several occasions. In addition, the interpretation of the drug concentration of a patient should be performed on an individual basis, taking into account the clinical condition of the patient. Important factors herewith are viral load, immunology, occurrence of adverse events, resistance pattern and comedication. In spite of the described constraints, the aim of this review is to provide a practical guide for TDM of antiretroviral agents. This article outlines pharmacokinetic target values for the HIV protease inhibitors amprenavir, atazanavir, indinavir, lopinavir, nelfinavir, ritonavir and saquinavir, and the non-nucleoside reverse transcriptase inhibitors efavirenz and nevirapine. Detailed advice is provided on how to interpret the results of TDM of these drugs.

Indinavir Plasma Concentration and Adherence Score Are Codeterminant of Early Virologic Response in HIV-Infected Patients of the APROCO Cohort

To study the respective roles of indinavir concentrations and treatment adherence as predictors of early virologic response, we analyzed the patients of the APROCO cohort treated by indinavir 800 mg TID during the first 4 months. Minimum (Cmin), maximum (Cmax), and the ratio of the measured to expected concentrations (CR) were estimated for each patient at M4, from a population pharmacokinetic analysis of all data. The relationship among virologic success at M4 [plasma HIV RNA (VL) <500 copies/mL], baseline characteristics, estimated indinavir concentrations, and adherence score measured by a self-administered questionnaire, was analyzed by multivariate logistic regression. In the 216 studied patients, baseline median HIV RNA was 4.4 log10 copies/mL, and CD4 cell count was 309/mm. Virologic success was achieved in 195 (90%) patients; it was independently related to baseline viral load (OR = 0.524, CI 0.29-0.93; P = 0.03), antiretroviral treatment naive status (OR = 3.89, CI 1.29-11.76; P = 0.01), and indinavir Cmin (OR = 1.06, CI 1.02-1.10; P = 0.004) when adherence score was not included in the model, whereas full adherence was the only independent related factor when included in the model (OR = 8.8, 95% CI 2.85-27.3; P < 10). In the 168 fully adherent patients, virologic success was more frequent in patients with shorter duration of antiretrovirals at baseline (P = 0.03), lower baseline HIV RNA (P = 0.03), and higher indinavir CR (P < 10); the most discriminating Cmin cut-off was 194 ng/mL. Data on the relationship between indinavir plasma concentration and virologic success are therefore misleading without a concomitant assessment of adherence. These data suggest that any strategy of therapeutic drug monitoring must imply first a combined evaluation of plasma concentrations and adherence level and second an intervention target based on the results of both assessments.

Simplification of therapeutic drug monitoring for twice-daily regimens of lopinavir/ritonavir for HIV infection

Cost and inconvenience limit the application of full 12-hour pharmacokinetic (PK) analysis for routine therapeutic drug monitoring of antiretroviral medications. We explore whether lopinavir (LPV) and ritonavir (RTV) exposures can be estimated with limited sampling for patients taking twice-daily LPV/RTV. One hundred and one PK profiles from 81 patients, most receiving salvage therapies including twice-daily LPV/RTV, were obtained for the analysis. After a minimum of 2 weeks on a stable regimen, blood was drawn immediately before and at 1, 2, 4, 6, 8, 10, and 12 hours after a timed medication dose. Plasma drug concentrations were determined by a validated HPLC-MS-MS assay. Peak concentrations, evening troughs, and AUC0-12 h were entered into linear and log10-log10 linear regression models to determine the best correlation with LPV and RTV plasma concentrations using a maximum of 2 time points. The accuracy and precision of PK parameter estimates of the resultant models were tested on data collected for an additional 25 patients. Twelve models using various combinations of 2 timed LPV concentrations afforded accurate (maximum % bias = -6.45) and precise (relative standard deviation < 15%) estimates for the LPV peak concentration or AUC0-12h. Four sets of 2 concentrations provided simultaneous estimates of both PK parameters, with the best estimates derived from data collected at 2 and 6 hours postdose. Evening trough concentrations were the best estimators of the daily nadir; however, no adequate substitute for collecting blood 12 hours postdose emerged from this analysis.

The Influence of St. John’s Wort on the Pharmacokinetics and Protein Binding of Imatinib Mesylate

STUDY OBJECTIVE

To determine the effect of St. John's wort on the pharmacokinetics of imatinib mesylate.

DESIGN

Open-label, complete crossover, fixed-sequence, pharmacokinetic study.

SETTING

Clinical research center.

SUBJECTS

Ten healthy adult volunteers.

INTERVENTION

Single 400-mg oral doses of imatinib were administered before and after 2 weeks of treatment with St. John's wort 300 mg 3 times/day.

MEASUREMENTS AND MAIN RESULTS

The pharmacokinetics of imatinib were significantly altered by St. John's wort, with reductions of 32% in the median area under the concentration-time curve from time zero to infinity (p=0.0001), 29% in maximum observed concentration (p=0.005), and 21% in half-life (p=0.0001). Protein binding ranged from 97.7-90.3% (mean 94.9%), was concentration independent, and was not altered by St. John's wort. Therapeutic outcomes of imatinib have been shown to correlate with both dose and drug concentrations.

CONCLUSION

Coadministration of imatinib with St. John's wort may compromise imatinib's clinical efficacy.

Antiretrovirals, Part II: Focus on Non-Protease Inhibitor Antiretrovirals (NRTIs, NNRTIs, and Fusion Inhibitors)

The second in a series reviewing the HIV/AIDS antiretroviral drugs. This review summarizes the non-protease inhibitor antiretrovirals: nucleoside and nucleotide analogue reverse transcriptase inhibitors (NRTIs), the nonnucleoside reverse transcriptase inhibitors (NNRTIs), and cell membrane fusion inhibitors. In an overview format for primary care physicians and psychiatrists, this review presents the mechanism of action, side effects, toxicities, and drug interactions of these agents.

Extending antiretroviral therapy to resource-poor settings: implications for drug resistance

The emergence of drug resistance in human immunodeficiency virus type 1 (HIV-1) may limit the clinical benefits of antiretroviral therapy. There is no objective evidence that the risk of drug resistance is greater in resource-limited settings than in the developed world. Treatment programmes will be most successful at preventing the spread of drug resistance if they provide healthcare infrastructures to maximize the effectiveness of antiretroviral therapy through the use of potent and convenient combination regimens that achieve durable suppression of HIV-1 replication.

Pharmacokinetic Evaluation and Short-Term Activity of Stavudine, Nevirapine, and Nelfinavir Therapy in HIV-1???Infected Adults

OBJECTIVE

Evaluate pharmacokinetic interaction, short-term safety, and antiretroviral activity of stavudine (d4T), nevirapine (NVP), and nelfinavir (NFV) as combination HIV-1 therapy.

DESIGN

Prospective, open-label study investigating the pharmacokinetic interactions between d4T, NVP, and NFV and documenting short-term tolerability and virologic and immunologic activity.

METHODS

Twenty-five HIV-1-infected adults, naive to nonnucleoside reverse transcriptase inhibitors (NNRTIs) and protease inhibitors (PIs), < or = 6 months of d4T treatment, CD4 > or = 100 cells/mm, and viral load > = 5,000 copies/mL enrolled. All received NFV 750 mg 3 times daily and d4T 30-40 mg twice daily for 1 week, then added NVP at 200 mg once daily for 2 weeks and 200 mg twice daily thereafter. Steady-state pharmacokinetic parameters of NFV, AG1402 (metabolite of NFV), and d4T were compared before and after the addition of NVP.

RESULTS

No statistically significant changes in NFV or d4T pharmacokinetics were observed following the addition of NVP. Levels of AG1402 were suppressed 60-70%. Drug-related adverse events were seen at expected rates. At day 36, median viral load suppression was 2.0 log10 and absolute CD4 count increased by 111 cells/mm.

CONCLUSIONS

NVP administration did not significantly affect the steady-state pharmacokinetic parameters of NFV or d4T. The combination of d4T, NVP, and NFV induced rapid suppression of HIV-1 viral load and rises in CD4 cell count.

Pharmacodynamics and clinical use of anti-HIV drugs

Antiretroviral drug exposure has been linked to both antiviral efficacy and the development of toxicity and further research in this area is ongoing and necessary. Use of these data may have important implications for TDM of HAART regimens in clinical practice. TDM, in conjunction with an assessment of the patient's viral resistance in the form of an IQ, needs to be examined and validated in large clinical trials.

HIV infection and advanced age emerging epidemiological, clinical, and management issues

While the mean age of HIV/AIDS patients at first diagnosis is progressively rising, no updated epidemiological estimates, controlled clinical data, and randomized therapeutic trials, are available regarding clinical and laboratory response to antiretroviral therapy, safety of anti-HIV compounds and their associations, potential drug-drug interactions, short- and long-term toxicity, consequences on underlying disorders, or interactions with concomitant pharmacological regimens, in the elderly. The life expectancy of HIV-infected persons treated with highly active antiretroviral therapy (HAART) now approximates that of general population matched for age, while also AIDS definition itself has lost most of its epidemiological and clinical significance, thanks to the immunoreconstitution resulting from the large-scale use of potent HAART regimens. The increased survival of HIV-infected patients, the late recognition of other subjects with missed or delayed diagnosis are responsible for a further expected rise of mean age of HIV-infected individuals, so that the patient population aged 60-70 years or more is expected to increase in coming years. Unfortunately, the majority of therapeutic trials involving antiretroviral therapy, as well as antimicrobial chemoprophylaxis for AIDS-related opportunistic complications, have advanced age and/or concurrent end-organ disorders among main exclusion criteria, or the design of these studies does not allow to extrapolate data regarding older patients, compared with younger ones. The very limited data presently available seem to demonstrate that HAART has a virological efficacy in the elderly comparable with that of younger adults, but immunological recovery is often slower and blunted, although several studies clearly demonstrated that thymic function is preserved until late adult age. When facing an HIV-infected patient with advanced age, health care givers have to pay careful attention to eventual end-organ disorders, all possible pharmacological interactions, overlapping toxicity due to concurrent drug administration. All these issues may significantly interfere with HAART activity, patient's adherence to prescribed medications, and frequency and severity of untoward effects. The guidelines of antiretroviral therapy and those of treatment and prophylaxis of AIDS-related diseases deserve appropriate updates, paralleling the increasing mean age of HIV-infected population. Moreover, epidemiological figures need an increased focus on older age, while clinical trials specifically targeting on the elderly population are mandatory to have reliable data on all aspects of HAART administration in advanced age.

Intracellular Accumulation of Nelfinavir and Its Relationship to P-Glycoprotein Expression and Function in HIV-Infected Patients

Objective

To compare plasma and intracellular nelfinavir pharmacokinetics, and determine their relationship to P-glycoprotein (P-gp) expression and function in lymphocytes of HIV-infected patients.

Methods

A pharmacokinetic study of 12 patients receiving nelfinavir plus dual nucleoside analogue therapy. Blood samples were taken at intervals to 12 h. Peripheral blood mononuclear cells (PBMCs) were isolated by density gradient centrifugation, and nelfinavir extracted from cells in the presence of 60% methanol and evaporated to dryness. Both plasma and intracellular nelfinavir samples were assayed by high performance liquid chromatography linked to mass spectrometry. P-gp expression and function were measured by flow cytometric analysis. Data were analysed by non-compartmental analysis using WinNonLin pharmacokinetic software.

Results

The mean intracellular nelfinavir AUC0–12 (mean ±SE) was about ninefold higher than that of plasma (264 200 ±63420 vs 29250 ±6629 ng/ml/h; P<0.001, and intracellular Cmin and C0 values for nelfinavir were five- to sixfold higher than that of plasma (Cmin: 5712 ±2156 vs 1062 ±357 ng/ml; C0: 15860 ±3662 vs 2553 ±539 ng/ml; P<0.0005). The intracellular nelfinavir Cmax was 15-fold higher than plasma (59420 ±13940 vs 3986 ±822 ng/ml; P<0.0005). There were no differences between plasma and intracellular values for Tmax, elimination half-life or mean residence time. In patients chronically treated with nelfinavir mean P-gp expression was 8.85 ±1.3 MFI, there was no correlation between Pgp expression and either intracellular AUC0–12 (r=–0.35; P=0.29) or intracellular C0 values. There was a correlation between intracellular nelfinavir concentrations and P-gp function at baseline (r=0.59; P<0.05). Basal P-gp-mediated rhodamine efflux was 61.0 ±4.2%. In the presence of ritonavir, cellular rhodamine efflux decreased to 25.6 ±5.5% ( P=0.001), representing an additional reversible efflux potential of 56.1 ±9.78%. There was a strong correlation between plasma and intracellular AUC0–12 for nelfinavir (r=0.75; P=0.011).

Conclusions

Nelfinavir undergoes significant intracellular accumulation within the PBMCs of HIV-infected patients, which may be in part related to its moderate ability to inhibit P-gp-mediated drug efflux. The addition of ritonavir further reduced P-gp function. Intracellular accumulation of nelfinavir correlated with P-gp function but not P-gp expression, suggesting pump activity is substrate concentration-dependant. There was a significant correlation between plasma and intracellular nelfinavir concentrations, suggesting one is a good surrogate marker of the other.

Pharmacokinetic drug interactions with nevirapine

Treatment of HIV infection is a multi-drug issue. Not only are there drugs for the treatment of HIV but also concomitant drugs for opportunistic infections, complications arising from the anti-retroviral therapy and other conditions related to a chronic disease. To have any understanding of drug-drug interactions in HIV treatment we need to appreciate the importance of key pharmacological areas including: 1) how each drug in a regimen is eliminated; 2) the potential for a drug to either induce or inhibit metabolic enzymes and/or transporters; 3) the therapeutic index of each drug. It is impossible to memorise all the possible drug-drug interactions in HIV, therefore understanding how drugs are metabolised/eliminated and the potential for a particular drug to modify the pharmacokinetics of another has predictive value even when substantive data are unavailable. NNRTIs interact with cytochrome P450 (CYP450) enzymes both as substrates and inducers. Because of the inductive effects caution must be exercised when using with protease inhibitors (either boosted or un-boosted with ritonavir). In this situation therapeutic drug monitoring may play a role in optimising response. There needs to be care when using many drugs with NNRTIs e.g. methadone, oral contraceptives, rifampicin, and there are some definite contraindications. By understanding pharmacological principles, it is possible to optimise use of multi-drug regimens.

New anti-HIV protease inhibitors provide more treatment options

For several years, protease inhibitor (PI)-containing antiretroviral treatment (ART) regimens have demonstrated long-term virologic and immunologic benefits and good durability of response. However, first-generation PIs have been associated with high pill burdens, gastrointestinal side effects, perturbation of lipid levels and glucose metabolism, and, in some cases, food and hydration requirements. Coadministration of low-dose ritonavir with PIs has enhanced their pharmacokinetic profile (lower doses, fewer pills, less frequent dosing schedules) and pharmacodynamics (increased potency, especially against resistant viruses) but has also been associated with increases in lipid levels. Two new PIs, atazanavir and 908 (fosamprenavir), may offer salvageable PI treatment options and may also address issues of potency, tolerability, and convenience by requiring fewer pills and causing fewer lipid and glucose perturbations than current PI options. The availability of these novel PIs may improve longterm treatment options for many patients.

Efficacy and Durability of Nevirapine in Antiretroviral-Experienced Patients

The non-nucleoside reverse transcriptase inhibitor (NNRTI) nevirapine (NVP) has been used as a component of salvage therapy for patients who have experienced virologic failure while taking nucleosides and protease inhibitors (PIs). In spite of broad cross-resistance within the NNRTI class, NVP may also play a role in salvage therapy for patients who have experienced failure while taking NNRTIs Another role for NVP in treatment-experienced patients is in so-called "PI switch" strategies, in which NVP is substituted for a PI within a virologically successful combination regimen. This paper reviews the clinical data that support the use of NVP in salvage regimens and PI switch strategies.

Subtherapeutic antiretroviral plasma concentrations in routine clinical outpatient HIV care

The objective of this study was to evaluate plasma concentrations of nonnucleoside reverse transcriptase inhibitors (NNRTIs) and protease inhibitors (PIs) within several dosing schemes in a cohort of HIV-infected patients in routine clinical practice and to find possible explanations for subtherapeutic plasma concentrations. Patients were included if a PI or NNRTI was part of their antiretroviral regimen, at least one plasma concentration was obtained, and a complete medication overview from community pharmacy records was available. The study period was from January 1998 to September 2001. Each plasma concentration was related to median plasma concentrations of a pharmacokinetic reference curve, yielding a concentration ratio (CR). A cutoff CR was defined for each antiretroviral drug per specific regimen, discriminating between >or=therapeutic and subtherapeutic concentrations. For the patients with subtherapeutic concentrations, it was sorted out whether drug interactions, adverse events and self-reported symptoms, or nonadherence could be the cause of the lower than expected plasma concentration. Ninety-seven HIV-infected patients fulfilled the criteria. During the defined period, 1145 plasma concentrations were available (median, 11; interquartile range, 8-14). Three hundred fourteen (27.4%) plasma concentrations were classified subtherapeutic. Drug interactions (2; 0.6%), adverse events and self-reported symptoms (67; 21.3%), and nonadherence (14; 4.5%) could only partly explain the subtherapeutic drug levels. Consequently, a large number of the subtherapeutic plasma concentrations (73.6%) remained inexplicable. A high number of subtherapeutic plasma concentrations were observed. No clear causes were found; thus, corrective measures will be difficult to employ. Therefore, therapeutic drug monitoring (TDM) must maintain its crucial place in routine clinical care to be able to identify patients who need extra attention so that therapeutic plasma concentrations are achieved.

Indinavir, efavirenz, and abacavir pharmacokinetics in human immunodeficiency virus-infected subjects

Adult AIDS Clinical Trials Group (AACTG) Protocol 886 examined the dispositions of indinavir, efavirenz, and abacavir in human immunodeficiency virus-infected subjects who received indinavir at 1,000 mg every 8 h (q8h) and efavirenz at 600 mg q24h or indinavir at 1,200 mg and efavirenz at 300 mg q12h with or without abacavir 300 at mg q12h. Thirty-six subjects participated. The median minimum concentration in plasma (C(min)) for indinavir administered at 1,200 mg q12h was 88.1 nM (interquartile range [IR], 61.7 to 116.5 nM), whereas the median C(min) for indinavir administered at 1,000 mg q8h was 139.3 nM (IR, 68.8 to 308.7 nM) (P = 0.19). Compared to the minimum C(min) range for wild-type virus (80 to 120 ng/ml) estimated by the AACTG Adult Pharmacology Committee, the C(min) for indinavir administered at 1,200 mg q12h (54 ng/ml) is inadequate. The apparent oral clearance (CL/F) (P = 0.28), apparent volume of distribution at steady state (V(ss)/F) (P = 0.25), and half-life (t(1/2)) (P = 0.80) of indinavir did not differ between regimens. The levels of efavirenz exposure were similar between regimens. For efavirenz administered at 600 mg q24h and 300 mg q12h, the median maximum concentrations in plasma (C(max)s) were 8,968 nM (IR, 5,784 to 11,768 nM) and 8,317 nM (6,587 to 10,239 nM), respectively (P = 0.66), and the C(min)s were 4,289 nM (IR, 2,462 to 5,904 nM) and 4,757 nM (IR, 3,088 to 6,644 nM), respectively (P = 0.29). Efavirenz pharmacokinetic parameters such as CL/F (P = 0.62), V(ss)/F (P = 0.33), and t(1/2) (P = 0.37) were similar regardless of the dosing regimen. The median C(max), C(min), CL/F, V(ss)/F, and t(1/2) for abacavir were 6,852 nM (IR, 5,702 to 7,532), 21.0 nM (IR, 21.0 to 87.5), 43.7 liters/h (IR, 37.9 to 55.2), 153.9 liters (IR, 79.6 to 164.4), and 2.0 h (IR, 1.8 to 2.8), respectively. In summary, when indinavir was given with efavirenz, the trough concentration of indinavir after administration of 1,200 mg q12h was inadequate. Abacavir did not influence the pharmacokinetics or exposure parameters of either indinavir or efavirenz. The levels of efavirenz exposure were similar in subjects receiving efavirenz q12h or q24h.

Reverse phase high-performance liquid chromatography method for the analysis of amprenavir, efavirenz, indinavir, lopinavir, nelfinavir and its active metabolite (M8), ritonavir, and saquinavir in heparinized human plasma

The increasing interest in applying therapeutic drug monitoring (TDM) to antiretroviral therapy is related to the observed interindividual variation in antiretroviral pharmacokinetics that results in a wide range of drug exposure from fixed-dosing regimens and the rapid evolution in the availability of phenotypic assays that generate a target 50% inhibitory concentration (e.g., IC(50)) as a basis for adjusting individual antiretroviral dosages. To facilitate the application of TDM, a method for the simultaneous determination of eight species has been developed. This method is used to quantitate efavirenz and the following protease inhibitors: amprenavir, indinavir, lopinavir, nelfinavir and its active metabolite (M8), ritonavir, and saquinavir. The method using reversed-phase high-performance liquid chromatography (RP-HPLC) was validated. Detection is effected using a photodiode-array detector (PDA) scanning at four different wavelengths. This method allows for detection of all analytes to a lower limit of quantitation of 0.1 to 0.2 microg/mL with an interday variation in CV ranging from 3.5% to 10.4%. The method is being applied to a TDM program that is currently being implemented in the authors' laboratory.

Therapeutic drug monitoring of nelfinavir and indinavir in treatment-naive HIV-1-infected individuals

BACKGROUND

Both virological failure and the toxicity of HIV protease inhibitors have been related to interindividual variability of plasma drug concentrations. Therapeutic drug monitoring (TDM) offers the possibility to detect patients with drug concentrations outside therapeutic ranges, who can subsequently benefit from dose modifications.

METHODS

ATHENA was a randomized controlled clinical trial. Subjects were randomly assigned to either a TDM group, in which the results of drug concentration measurements plus advice were reported to their treating physician, or to a control group for whom TDM results were not reported. This analysis refers to treatment-naive patients who started a regimen containing indinavir or nelfinavir before November 1999.

FINDINGS

A total of 147 patients were randomly assigned: 92 to nelfinavir, 55 to indinavir. After one year of follow-up significantly fewer patients in the TDM group had discontinued nelfinavir or indinavir than in the control group: 17.4 versus 39.7%. This was mainly driven by a significantly lower rate of discontinuation because of virological failure in nelfinavir patients: 2.4% in the TDM group versus 17.6% in the control group, and by a non-significant difference in the rate of discontinuation because of toxicity in indinavir patients: 14.3% in the TDM group versus 29.6% in the control group. In a non-completer equals failure analysis of all randomized patients, the TDM group showed a significantly higher proportion of patients with a viral load below 500 copies after 12 months of treatment (78.2 versus 55.1%).

INTERPRETATION

TDM of nelfinavir and indinavir in treatment-naive patients improves treatment response.

Drug interactions between antiretroviral drugs and comedicated agents

HIV-infected individuals usually receive a wide variety of drugs in addition to their antiretroviral drug regimen. Since both non-nucleoside reverse transcriptase inhibitors and protease inhibitors are extensively metabolised by the cytochrome P450 system, there is a considerable potential for pharmacokinetic drug interactions when they are administered concomitantly with other drugs metabolised via the same pathway. In addition, protease inhibitors are substrates as well as inhibitors of the drug transporter P-glycoprotein, which also can result in pharmacokinetic drug interactions. The nucleoside reverse transcriptase inhibitors are predominantly excreted by the renal system and may also give rise to interactions. This review will discuss the pharmacokinetics of the different classes of antiretroviral drugs and the mechanisms by which drug interactions can occur. Furthermore, a literature overview of drug interactions is given, including the following items when available: coadministered agent and dosage, type of study that is performed to study the drug interaction, the subjects involved and, if specified, the type of subjects (healthy volunteers, HIV-infected individuals, sex), antiretroviral drug(s) and dosage, interaction mechanism, the effect and if possible the magnitude of interaction, comments, advice on what to do when the interaction occurs or how to avoid it, and references. This discussion of the different mechanisms of drug interactions, and the accompanying overview of data, will assist in providing optimal care to HIV-infected patients.

Intracellular Indinavir Pharmacokinetics in HIV-Infected Patients: Comparison with Plasma Pharmacokinetics

Objective

To determine intracellular concentrations of indinavir (IDV) and investigate the relationship between plasma and intracellular IDV pharmacokinetics in HIV-infected patients.

Methods

A pharmacokinetic study of 10 patients receiving IDV plus dual nucleoside analogue therapy. Peripheral blood mononuclear cells were isolated by density gradient centrifugation and cell counts estimated. IDV was extracted from cells in the presence of 60% methanol and evaporated to dryness. Both plasma and intracellular IDV samples were assayed by high performance liquid chromatography linked to mass spectrometry. Data were subjected to non-compartmental pharmacokinetic analysis.

Results

The mean intracellular IDV area under the curve over 8 h (AUC0-8) was lower than the plasma AUC0-8 (7574 ±1003 vs 25060 ±4171 ng/ml/h; P<0.004). However, both the elimination half-life (t1/2) and the mean residence time (MRT) of IDV intracellularly were prolonged compared with plasma (t1/2: 2.0 ±0.3 vs 1.2 ±0.09 h; MRT: 3.6 ±0.6 vs 2.1 ±0.1 h; P<0.05). All patients were responsive to therapy at the time of the study, as assessed by HIV plasma RNA levels. Individual plasma versus intracellular time course results suggest that, due to the prolonged intracellular half-life, some patients may achieve acceptable intracellular IDV concentrations despite sub-therapeutic plasma levels. Similarly, potentially inadequate intracellular concentrations may occur despite therapeutic plasma concentrations.

Conclusions

There is no significant intracellular accumulation of IDV within the lymphocytes of HIV-1-infected patients relative to plasma. However, intracellular concentrations are compatible with reported IDV-free drug concentrations in plasma. The intracellular elimination half-life and mean residence time of IDV are significantly prolonged compared with plasma. This may in part explain why certain patients maintain adequate viral suppression despite sub-therapeutic plasma IDV levels.

Treatment failure of nelfinavir-containing triple therapy can largely be explained by low nelfinavir plasma concentrations

The relationship between plasma concentrations of nelfinavir and virologic treatment failure was investigated to determine the minimum effective concentration of nelfinavir. Plasma samples were prospectively collected from treatment-naive patients who began taking nelfinavir, 1,250 mg BID + two nucleoside reverse transcription inhibitors (NRTIs). Nelfinavir concentration ratios were calculated by dividing each individual nelfinavir level by the time-adjusted population value. Virologic failure was defined as either no response (a detectable viral load after 6 months) or a relapse (detectable viral load after being undetectable, or an increase in viral load >1 log above nadir). Forty-eight patients were included with a median follow-up period of 8 months. The median concentration ratio of nelfinavir was 0.98 (interquartile range, 0.76-1.47). Virologic failure was observed in 29% of the patients. In a univariate analysis, the nelfinavir concentration ratio appeared to be the single determinant that was related to virologic failure (P = 0.039). Patients with a median ratio <0.90 had a relative risk of 3.0 (95% CI, 1.2-7.6) for virologic failure. Using this threshold, virologic failures were detected with 64% sensitivity and 74% specificity (P = 0.014). Virologic failure of nelfinavir-containing triple therapy can be explained, to a large extent, by low plasma levels of nelfinavir.

Nevirapine or lamivudine plus stavudine and indinavir: examples of 2-class versus 3-class regimens for the treatment of human immunodeficiency virus type 1

We compared use of a 3-class regimen (nevirapine [Nvp], stavudine [d4T], and indinavir [Idv; 1000 mg 3 times daily]) with use of a 2-class regimen (lamivudine [3TC], d4T, and Idv [800 mg 3 times daily]) for 145 patients infected with human immunodeficiency virus type 1 (HIV-1). At week 72, the plasma HIV-1 RNA level was undetectable in 52% of Nvp recipients versus 79% of 3TC recipients (P<.001). Idv trough levels were 81 ng/mL in the Nvp group and 99 ng/mL in the 3TC group (P=.012). In the Nvp group, 42.5% of patients discontinued the study regimen; in the 3TC group, 22.5% of patients discontinued therapy (P=.013). The rate of resistance to nonnucleoside analogue reverse-transcriptase inhibitors among patients in the Nvp group with virological failure was not different from the rate of resistance to 3TC among patients in the 3TC group with virological failure. These results do not support the use of a 3-class regimen that includes Nvp for patients with no or limited exposure to nucleoside analogues.

Therapeutic drug monitoring of HIV-protease inhibitors to assess noncompliance

OBJECTIVE

To determine plasma concentration ratio limits (CORALS) for HIV-protease inhibitors outside of which random plasma concentrations reflect partial compliance or noncompliance. In the absence of a gold standard for measuring compliance and to avoid complex techniques, measuring plasma concentrations may be an objective and easy way to check noncompliance.

METHODS

Pharmacokinetic curves after observed ingestion were recorded in patients on steady-state indinavir 800 mg TID (n = 22), ritonavir 400 mg/saquinavir 400 mg BID (n = 22, ritonavir; n = 17, saquinavir hard-gel capsules), or nelfinavir 750 mg TID (n = 4) or 1250 mg BID (n = 4). Concentration ratios were calculated by dividing the measured concentration by the median population value at the corresponding sampling time. Limits were based on the minimum P(05) (5th percentile) and maximum P(95) of these ratios found during the sampling interval. With these limits the authors determined (1) the proportion of patients falsely judged as noncompliers after observed ingestion, (2) discrimination between compliers and noncompliers, and (3) the absolute percentage of noncompliers. To judge the last two elements, two sets of random plasma samples were included: (1) samples sent in by the physician on suspicion of noncompliance (indinavir, n = 42; nelfinavir, n = 22;) or from a study population stating imperfect compliance in a questionnaire (ritonavir/saquinavir, n = 11); (2) control samples sent in routinely for monitoring therapeutic levels (indinavir, n = 41; nelfinavir, n = 201) or drawn from patients who stated perfect compliance in the questionnaire (ritonavir/saquinavir, n = 35).

RESULTS

The following CORALS were found: indinavir <0.23 or >3.3; nelfinavir <0.36 or >2.1; ritonavir <0.18 or >1.9; saquinavir <0.28 or >2.3. In 31% to 55% of the patients suspected of noncompliance a plasma concentration ratio outside these limits was found. If a ratio was outside the limits, there was a 68% to 88% chance that that plasma sample belonged to a patient suspected of noncompliance, compared with the controls (all Chi-squared tests < 0.05). Compared with observed ingestion, these chances ranged from 87% to 92%.

CONCLUSION

By using concentration ratio limits (CORALS), plasma samples of protease inhibitors with values outside these limits are highly indicative of partial or noncompliance.

Position paper on therapeutic drug monitoring of antiretroviral agents

Monitoring drug concentrations in humans to optimize efficacy and reduce toxicity is not a new concept in clinical pharmacology. It has been successfully applied to many different classes of drugs. As a result of considerable concentration and response data, the concept of therapeutic drug monitoring (TDM) has been expanded to certain antiretroviral compounds. In particular, protease inhibitors and nonnucleoside reverse transcriptase inhibitors may be viable candidates for TDM, and limited clinical trial data suggest monitoring plasma concentrations of these agents may indeed clinically benefit patients with HIV infection. A primary distinction between TDM of antiretroviral drugs compared with other drugs is that multiple agents are concomitantly used to treat HIV infection. As with all illnesses that require self-administered drug therapy, poor adherence is a major impediment to success. However, in the treatment of HIV infection, inadequate drug concentrations will result in the appearance or evolution of drug resistance mutations that can endanger present and future drug treatment options. Procedures for sample collection, cross-validation of analytical procedures, and interpretation of assay results should be standardized. More clinical data are needed to confirm this approach and methods of implementing TDM should be further explored. This position paper offers guidelines to aid clinicians who choose to incorporate TDM into the routine care of their patients.

Critical issues in therapeutic drug monitoring of antiretroviral drugs

The interest in therapeutic drug monitoring (TDM) of antiretroviral drugs is growing rapidly. For the protease inhibitors, and to a lesser extent for the non-nucleoside reverse transcriptase inhibitors, relationships between plasma drug concentrations and their efficacy and toxicity have been identified. Furthermore, the pharmacokinetics of especially the protease inhibitors vary widely between patients, suggesting a role for TDM to individualize antiretroviral therapy. Recently, randomized, prospective clinical trials evaluating the role of TDM in the management of HIV-1-infected patients showed promising results. However, there are still many questions to be answered before large-scale introduction of TDM can be justified (e.g., which pharmacokinetic parameter should be optimized, and what is the minimal effective concentration). This review summarizes the basis for TDM of antiretroviral drugs and discusses the problems and prospects of this potential tool in the care for HIV-1-infected individuals.