Population pharmacokinetics of nevirapine, zidovudine, and didanosine in human immunodeficiency virus-infected patients. The National Institute of Allergy and Infectious Diseases AIDS Clinical Trials Group Protocol 241 Investigators

Amiodarone/N-desethylamiodarone population pharmacokinetics in pediatric patients

The population pharmacokinetics (PK) of amiodarone and its active metabolite, N-desethylamiodarone (DEA) were investigated in pediatric patients with arrhythmias, mainly supraventricular tachycardias. A total of 55 patients from the department of pediatric intensive care and pediatric cardiology at Necker Enfants-malades Hospital (Paris, France) provided 72 concentrations for both amiodarone and DEA following repeated oral or intravenous administration. Blood samples drawn for biological analyses were used for drug concentrations. Plasma amiodarone concentrations were measured by a liquid chromatography method coupled with mass spectrometry (LC-MS/MS) and the data were modelled using the software Monolix 2019R2. Parent pharmacokinetics was described with a two-compartment open model and the metabolite formation was connected to the central parent compartment. Parameter estimates scaled allometrically on body weight (normalized to 70 kg) were respectively (% relative standard errors or RSE) 6.32 (31%) and 7.14 L/h (26%) for elimination (CL) and intercompartmental clearances and 167 (31%) and 3930 (32%) L for V₁ and V₂ . Oral bioavailability was 0.362 (21.5%). The clearance between subject variability (ω, square root of the variance) was 0.462 (RSE 21%). The proportional residual variabilities were respectively 0.453 (RSE 13%) and 0.423 (RSE 12%) for amiodarone and DEA respectively. The terminal half-lives were 34 and 14.5 days for amiodarone and DEA respectively. A dosage schedule was established for 3 weight bands along 2 time periods. The high pharmacokinetic variability suggests that therapeutic drug monitoring (TDM) might be useful to improve individual efficacy and safety.

Nevirapine pharmacokinetics in HIV-infected persons receiving rifapentine and isoniazid for TB prevention

BACKGROUND

The use of rifamycin antibiotics for TB prevention carries a risk of detrimental drug-drug interactions with concomitantly used ART.

OBJECTIVES

To evaluate the interaction of the antiretroviral drug nevirapine in combination with 4 weeks of daily rifapentine and isoniazid for TB prevention in people living with HIV.

METHODS

Participants were individuals enrolled in the BRIEF-TB study receiving nevirapine and randomized to the rifapentine/isoniazid arm of the study. Participants provided sparse pharmacokinetic (PK) sampling at baseline and weeks 2 and 4 for trough nevirapine determination. Nevirapine apparent oral clearance (CL/F) was estimated and the geometric mean ratio (GMR) of CL/F prior to and during rifapentine/isoniazid was calculated.

RESULTS

Seventy-eight participants had evaluable PK data: 61 (78%) female, 51 (65%) black non-Hispanic and median (range) age of 40 (13-66) years. Median (IQR) nevirapine trough concentrations were: week 0, 7322 (5266-9302) ng/mL; week 2, 5537 (3552-8462) ng/mL; and week 4, 5388 (3516-8243) ng/mL. Sixty out of 78 participants (77%) had nevirapine concentrations ≥3000 ng/mL at both week 2 and 4. Median (IQR) nevirapine CL/F values were: week 0 pre-rifapentine/isoniazid, 2.03 (1.58-2.58) L/h; and during rifapentine/isoniazid, 2.62 (1.81-3.42) L/h. The GMR (90% CI) for nevirapine CL/F was 1.30 (1.26-1.33).

CONCLUSIONS

The CL/F of nevirapine significantly increased with concomitant rifapentine/isoniazid. The decrease in nevirapine trough concentrations during rifapentine/isoniazid therapy suggests induction of nevirapine metabolism, consistent with known rifapentine effects. The magnitude of this drug-drug interaction suggests daily rifapentine/isoniazid for TB prevention should not be co-administered with nevirapine-containing ART.

The impact of age on antiretroviral drug pharmacokinetics in the treatment of adults living with HIV

INTRODUCTION

People living with HIV (PLWH) are aging and will receive life-long treatment: despite substantial improvement in drug efficacy and tolerability, side effects still occur and they can blunt antiretroviral treatment effectiveness. Since age may affect drug exposure and may be associated with side-effects we aimed at reviewing available data on the effect of age on antiretrovirals' pharmacokinetics in adult patients.

AREAS COVERED

We searched public databases and major conference proceedings for data on age and pharmacokinetics/pharmacodynamics in PLWH. We limited our review to currently used drugs and focused on population pharmacokinetics and physiologically-based pharmacokinetic modeling studies.

EXPERT OPINION

Available evidence of a potential detrimental effect in elderly PLWH is limited by study design and small sample sizes. Careful consideration of undoubtful benefits and potential harms is advised when prescribing ARVs to geriatric patients and the knowledge of pharmacokinetics changes need to be included in the process. With the 'greying' of the pandemic we need studies with a specific focus on geriatric patients living with HIV that will consider specific phenotypes and associated changes (including sarcopenia).

Singularities of nevirapine metabolism: from sex-dependent differences to idiosyncratic toxicity

Nevirapine (NVP) is a first-generation non-nucleoside reverse transcriptase inhibitor widely used for the treatment and prophylaxis of human immunodeficiency virus infection. The drug is taken throughout the patient's life and, due to the availability of an extended-release formulation, it is administered once daily. This antiretroviral is one of the scarce examples of drugs with prescription criteria based on sex, in order to prevent adverse reactions. The therapy with NVP has been associated with potentially life-threatening liver and idiosyncratic skin toxicity. Multiple evidence has emerged regarding the formation of electrophilic NVP metabolites as crucial for adverse idiosyncratic reactions. The formation of reactive metabolites that yield covalent adducts with proteins has been demonstrated in patients under NVP-based treatment. Interestingly, several pharmacogenetic- and sex-related factors associated with NVP toxicity can be mechanistically explained by an imbalance toward increased formation of NVP-derived reactive metabolites and/or impaired detoxification capability. Moreover, the haptenation of self-proteins by these reactive species provides a plausible link between NVP bioactivation and immunotoxicity, further supporting the relevance of this toxicokinetics hypothesis. In the current paper, we review the existing knowledge and recent developments on NVP metabolism and their relation to NVP toxicity.

Novel Polymyxin Combination with the Antiretroviral Zidovudine Exerts Synergistic Killing against NDM-Producing Multidrug-Resistant Klebsiella pneumoniae

Polymyxins are used as a last-line therapy against multidrug-resistant (MDR) New Delhi metallo-β-lactamase (NDM)-producing Klebsiella pneumoniae However, polymyxin resistance can emerge with monotherapy; therefore, novel strategies are urgently needed to minimize the resistance and maintain their clinical utility. This study aimed to investigate the pharmacodynamics of polymyxin B in combination with the antiretroviral drug zidovudine against K. pneumoniae Three isolates were evaluated in static time-kill studies (0 to 64 mg/liter) over 48 h. An in vitro one-compartment pharmacokinetic/pharmacodynamic (PK/PD) model (IVM) was used to simulate humanized dosage regimens of polymyxin B (4 mg/liter as continuous infusion) and zidovudine (as bolus dose thrice daily to achieve maximum concentration of drug in broth [C _max] of 6 mg/liter) against K. pneumoniae BM1 over 72 h. The antimicrobial synergy of the combination was further evaluated in a murine thigh infection model against K. pneumoniae 02. In the static time-kill studies, polymyxin B monotherapy produced rapid and extensive killing against all three isolates followed by extensive regrowth, whereas zidovudine produced modest killing followed by significant regrowth at 24 h. Polymyxin B in combination with zidovudine significantly enhanced the antimicrobial activity (≥4 log₁₀ CFU/ml) and minimized bacterial regrowth. In the IVM, the combination was synergistic and the total bacterial loads were below the limit of detection for up to 72 h. In the murine thigh infection model, the bacterial burden at 24 h in the combination group was ≥3 log₁₀ CFU/thigh lower than each monotherapy against K. pneumoniae 02. Overall, the polymyxin B-zidovudine combination demonstrates superior antimicrobial efficacy and minimized emergence of resistance to polymyxins.

Clinical and genetic determinants of nevirapine plasma trough concentration

Background:

Only few data are available on the influence of CYP2B6 and CYP3A4/A5 polymorphisms on nevirapine plasma concentrations in the Caucasian population. Our aim was to assess the impact of CYP2B6 and CYP3A4/A5 polymorphisms on nevirapine plasma concentrations consecutively collected.

Methods:

We retrospectively analyzed clinical data of all HIV-positive patients who were followed at the Infectious Diseases Unit, DIBIC Luigi Sacco, University of Milan between January 2000 and December 2015. All patients with at least one nevirapine plasma trough concentration (NVP C_min) determination were tested for CYP2B6 c.516 G>T, CYP3A4*22C>T and CYP3A5*3 A>G polymorphisms. Univariate and multivariate regression analyses were carried out considering NVP C_min as the dependent variable and genetic polymorphisms and clinical characteristics as independent variables.

Results:

A total of 143 patients were evaluated. Most of them were males (61.5%) and Caucasian (92.3%). Overall, NVP C_min varied from 1571 to 14,189  ng/mL (median  =  5063  ng/mL, interquartile range  =  3915–6854). The median NVP C_min significantly differed in patients with different CYP2B6 genotypes, but did not vary in those with different CYP3A phenotypes. In the final general linear model, factors significantly associated with a higher NVP C_min were each extra unit of T alleles of CYP2B6 rs3745274 (β  =  0.328, 95% confidence interval  =  0.172–0.484; p  <  0.0001), older age (β  =  0.362, 95% confidence interval  =  0.193–0.532; p  <  0.0001) and hepatitis C virus coinfection (β  =  0.161, 95% confidence interval  =  0.006–0.315; p  <  0.041).

Conclusion:

Our study, conducted in a prevalent Caucasian population, highlighted the importance of CYP2B6 genetic variants in influencing nevirapine plasma trough concentration. Furthermore, older age and hepatitis C virus coinfection significantly increase exposure to nevirapine.

Sex-dependent metabolism of nevirapine in rats: impact on plasma levels, pharmacokinetics and interaction with nortriptyline

Nevirapine (NVP) is a non-nucleoside reverse transcriptase inhibitor (NNRTI) widely used in the treatment of human immunodeficiency virus type 1 (HIV-1) and is the first-choice NNRTI during pregnancy. NVP shows a sex dimorphic profile in humans with sex differences in bioavailability, biotransformation and toxicity. In this study, sex differences in NVP metabolism and inhibition of NVP metabolism by the antidepressant nortriptyline (NT) were evaluated using rats as experimental animals. NVP was administered orally to male and female rats and sex differences in plasma levels and pharmacokinetic parameters were analysed. NVP plasma levels were higher in female compared with male rats, and pharmacokinetic parameters such as maximum plasma concentration (C_max), time to C_max (T_max), half-life (t_1/2) and area under the plasma concentration-time curve from the time of dosing to the last measurable concentration (AUC_last) showed ca. 4-, 5-, 7- and 22-fold higher values in female rats. In vitro experiments carried out with hepatic microsomes confirmed slower NVP metabolism in female rats, with a maximum velocity (V_max) 2-fold lower than in male hepatic microsomes. The major metabolite in both sexes was 12-hydroxynevirapine (12-OH-NVP), with the V_max for this metabolite being 15-fold lower in female compared with male rat hepatic microsomes. Inhibition of NVP metabolism by NT was similar in both sexes, with statistically non-significant differences in 50% inhibitory concentration (IC₅₀) values. In summary, NVP is metabolised more slowly in female compared with male rats, but the inhibitory effect of NT is similar in both sexes.

Effect of diurnal variation, CYP2B6 genotype and age on the pharmacokinetics of nevirapine in African children

OBJECTIVES

To characterize the effects of CYP2B6 polymorphisms, diurnal variation and demographic factors on nevirapine pharmacokinetics in African children.

METHODS

Non-linear mixed-effects modelling conducted in NONMEM 7.3 described nevirapine plasma concentration-time data from 414 children aged 0.3-15 years.

RESULTS

Nevirapine pharmacokinetics was best described using a one-compartment disposition model with elimination through a well-stirred liver model accounting for a first-pass effect and transit-compartment absorption. Intrinsic clearance was affected by diurnal variation (characterized using a cosine function with peak amplitude 29% at 12 noon) and CYP2B6 metabolizer status [extensive metabolizer (EM) 516GG|983TT, reference; intermediate metabolizer (IM) 516GT|983TT or 516GG|983TC, 17% lower; slow metabolizer (SM) 516TT|983TT or 516GT|983TC, 50% lower; ultra-slow metabolizer (USM) 516GG|983CC, 68% lower]. Age was found to affect pre-hepatic bioavailability: 31.7% lower at birth and increasing exponentially. Median (90% CI) evening Cmin values in the different metabolizer groups were 5.01 (3.01-7.47), 6.55 (3.65-13.32), 11.59 (5.44-22.71) and 12.32 (12.32-27.25) mg/L, respectively. Evening Cmin values were <3 mg/L in 43% of EM weighing <6 kg and 26% of IM weighing <6 kg, while 73% of SM and 88% of USM in all weight-bands had evening Cmin values >8 mg/L. Cmin was not markedly affected by administration time, but was altered by unequal splitting of the daily dose.

CONCLUSIONS

Diurnal variation does not greatly affect nevirapine exposure. However, when daily doses cannot be split equally, the larger dose should be given in the morning. To achieve homogeneous exposures, nevirapine doses for SM and USM should be reduced by 50%, and children weighing <6 kg with EM or IM metabolizer status should receive the same dose as children weighing 6-10 kg.

Lopinavir/ritonavir plus lamivudine and abacavir or zidovudine dose ratios for paediatric fixed-dose combinations

BACKGROUND

Lopinavir/ritonavir (LPV/r) is available in a liquid formulation that is far from ideal for treatment of children in resource-poor settings. Flexible, low-cost, solid, oral fixed-dose combinations (FDC) of LPV/r with nucleoside reverse transcriptase inhibitors (LPV/r/abacavir [ABC]/lamivudine [3TC] and LPV/r/zidovudine [ZDV]/3TC) are needed to improve both management and adherence of children. This work aimed to develop appropriate drug ratios and dosing for each FDC.

METHODS

Data from 25 combined datasets included therapeutic drug monitoring and clinical studies from IMPAACT and PENTA. Population pharmacokinetic analyses were performed using Monolix. Monte-Carlo simulations of WHO and FDA dosing recommendations were performed to assess their ability to provide optimal exposure in children weighing 4 to 25 kg based on consensus plasma targets. The LPV/r:3TC:ZDV(ABC) dose ratios were 2.67:1:2(2), respectively.

RESULTS

Using WHO dosage, LPV efficacy target was reached in all weight bands. Given the recommended drug ratios, the dosage for the 4-5.9 kg weight band (LPV/ZDV: 120/90 mg twice daily [bid]) showed more than 20% of subjects had ZDV levels at high risk of neutropenia. Reducing the LPV/ZDV dose to 80/60 mg bid decreased frequency of high ZDV concentrations but retained the LPV efficacy criteria.

CONCLUSIONS

This defined a flexible and simple FDC containing 40 mg LPV, 10 mg ritonavir, 15 mg 3TC and 30 mg ABC or ZDV. According to the weight bands defined by WHO, 4-5.9 kg, 6-9.9 kg, 10-13.9 kg, 14-19.9 kg, 20-24.9 kg, therapeutic doses would be 2, 3, 4, 5 or 6 individual units administered by oral route bid.

Caring for women living with HIV: gaps in the evidence

Introduction

In the management of HIV, women and men generally undergo the same treatment pathway, with gender differences being given limited consideration. This is in spite of accumulating evidence that there are a number of potential differences between women and men which may affect response to treatment, pharmacokinetics, toxicities and coping. There are also notable psychological, behavioural, social and structural factors that may have a unique impact on women living with HIV (WLWH). Despite our increasing knowledge of HIV and advances in treatment, there are significant gaps in the data relating specifically to women. One of the factors contributing to this situation is the under-representation of women in all aspects of HIV clinical research. Furthermore, there are clinical issues unique to women, including gynaecologic and breast diseases, menopause-related factors, contraception and other topics related to women's and sexual health.

Methods

Using scoping review methodology, articles from the literature from 1980 to 2012 were identified using appropriate MeSH headings reflecting the clinical status of WLWH, particularly in the areas of clinical management, sexual health, emotional wellbeing and treatment access. Titles and abstracts were scanned to determine whether they were relevant to non-reproductive health in WLWH, and papers meeting inclusion criteria were reviewed.

Results

This review summarizes our current knowledge of the clinical status of WLWH, particularly in the areas of clinical management, sexual health, emotional wellbeing and treatment access. It suggests that there are a number of gender differences in disease and treatment outcomes, and distinct women-specific issues, such as menopause and co-morbidities, that pose significant challenges to the care of WLWH.

Conclusions

Based on a review of this evidence, outstanding questions and areas where further studies are required to determine gender differences in the efficacy and safety of treatment and other clinical and psychological issues specifically affecting WLWH have been identified. Well-controlled and adequately powered clinical studies are essential to help provide answers to these questions and to contribute to activities aimed at improving the health and wellbeing of WLWH.

Population pharmacokinetics study of recommended zidovudine doses in HIV-1-infected children

The aims of this study were to describe the pharmacokinetics of zidovudine (ZDV) and its biotransformation to its metabolite, 3*-azido-3*-deoxy-5*-glucuronylthymidine (G-ZDV), in HIV-infected children, to identify factors that influence the pharmacokinetics of ZDV, and to compare and evaluate the doses recommended by the World Health Organization (WHO) and the Food and Drug Administration (FDA). ZDV concentrations in 782 samples and G-ZDV concentrations in 554 samples from 247 children ranging in age from 0.5 to 18 years were retrospectively measured. A population pharmacokinetic model was developed with NONMEM software (version 6.2), and the pharmacokinetics of ZDV were best described by a one-compartment model with first-order absorption and elimination. The effect of body weight on the apparent elimination clearance and volume of distribution was significant. The mean population parameter estimates were as follows: absorption rate, 2.86 h(-1); apparent elimination clearance, 89.7 liters · h(-1) (between-subject variability, 0.701 liters · h(-1)); apparent volume of distribution, 229 liters (between-subject variability, 0.807 liters); metabolic formation rate constant, 12.6 h(-1) (between-subject variability, 0.352 h(-1)); and elimination rate constant of G-ZDV, 2.27 h(-1). On the basis of simulations with FDA and WHO dosing recommendations, the probabilities of observing efficient exposures (doses resulting in exposures of between 3 and 5 mg/liter · h) with less adverse events (doses resulting in exposures below 8.4 mg/liter · h) were higher when the FDA recommendations than when the WHO recommendations were followed. In order to improve the FDA recommendations, ZDV doses should be reconsidered for the weight band (WB) of 20 to 40 kg. The most appropriate doses should be decreased from 9 to 8 mg/kg of body weight twice a day (BID) for the WB from 20 to 29.9 kg and from 300 to 250 mg BID for the WB from 30 to 39.9 kg. The highest dose, 300 mg BID, should be started from body weights of 40 kg.

Clinical pharmacokinetics of antiretroviral drugs in older persons

INTRODUCTION

Combination antiretroviral therapy has enabled HIV-infected persons to reach older ages in high numbers. Hepatic and renal changes that normally occur with advancing age occur earlier and with higher incidence in HIV-infected individuals. A limited number of prospective controlled studies have demonstrated small reductions (17 to 41%) in lopinavir, atazanavir and lamivudine clearance in older versus younger adults. A much larger number of retrospective studies in adults (age range ∼ 20 to 60 years), including all antiretroviral drugs, have evaluated age as a covariate for pharmacokinetics. Most studies did not detect substantial associations between drug exposures and age.

AREAS COVERED

This review summarizes antiretroviral drug pharmacokinetics in older persons. The authors review articles from PubMed (search terms: elderly, antiretroviral, pharmacokinetics) in addition to the bibliographies of those selected.

EXPERT OPINION

The evidence to date does not support major pharmacokinetic changes in adults between ∼ 20 and 60 years of age. However, additional prospective, well-controlled studies are needed in more persons > 60 years, including those with frailty and comorbidities, with assessment of unbound drug clearance, and incorporation of adherence, pharmacogenetics and concomitant medications. Until then, guidelines for drug-drug interactions and dosing in renal and hepatic impairment should be followed in older HIV-infected individuals.

Population-Based Assessments of Clinical Drug-Drug Interactions: Qualitative Indices or Quantitative Measures?

Population-based assessments of drug-drug interactions have become more common since the introduction and acceptance of the population pharmacokinetic approach. Unlike traditional methods, population-based studies provide clinically relevant results that can be applied directly to a target patient population. Furthermore, population-based studies do not demand the traditional requirements of intensive pharmacokinetic sampling, rigorous inpatient stays, or stringent assessment schedules. As such, the population-based approach can effectively be used to confirm known drug-drug interactions and further characterize anticipated interactions. A prospectively designed analysis can also reveal drug-drug interactions that might otherwise have gone undetected with traditional methods. Ultimately, these results could help to alleviate clinicians' concerns about using widely marketed drugs in combination therapies and also reduce patients' risk of experiencing unacceptable side effects. This article intends to provide a balanced overview of the population-based approach and its merits, drawbacks, and potential utility in the assessment of drug-drug interactions during clinical drug development.

Pharmacokinetics of phase I nevirapine metabolites following a single dose and at steady state

Nevirapine is one of the most extensively prescribed antiretrovirals worldwide. The present analyses used data and specimens from two prior studies to characterize and compare plasma nevirapine phase I metabolite profiles following a single 200-mg oral dose of nevirapine in 10 HIV-negative African Americans and a steady-state 200-mg twice-daily dose in 10 HIV-infected Cambodians. Nevirapine was assayed by high-performance liquid chromatography (HPLC). The 2-, 3-, 8- and 12-hydroxy and 4-carboxy metabolites of nevirapine were assayed by liquid chromatography-tandem mass spectrometry (LC/MS/MS). Pharmacokinetic parameters were calculated by noncompartmental analysis. The metabolic index for each metabolite was defined as the ratio of the metabolite area under the concentration-time curve (AUC) to the nevirapine AUC. Every metabolite concentration was much less than the corresponding nevirapine concentration. The predominant metabolite after single dose and at steady state was 12-hydroxynevirapine. From single dose to steady state, the metabolic index increased for 3-hydroxynevirapine (P < 0.01) but decreased for 2-hydroxynevirapine (P < 0.001). The 3-hydroxynevirapine metabolic index was correlated with nevirapine apparent clearance (P < 0.001). These findings are consistent with induction of CYP2B6 (3-hydroxy metabolite) and a possible inhibition of CYP3A (2-hydroxy metabolite), although these are preliminary data. There were no such changes in metabolic indexes for 12-hydroxynevirapine or 4-carboxynevirapine. Two subjects with the CYP2B6 *6*6 genetic polymorphism had metabolic indexes in the same range as other subjects. These results suggest that nevirapine metabolite profiles change over time under the influence of enzyme induction, enzyme inhibition, and host genetics. Further work is warranted to elucidate nevirapine biotransformation pathways and implications for drug efficacy and toxicity.

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.

Nevirapine exposure with WHO pediatric weight band dosing: enhanced therapeutic concentrations predicted based on extensive international pharmacokinetic experience

Nevirapine (NVP) is a nonnucleoside reverse transcriptase inhibitor (NNRTI) used worldwide as part of combination antiretroviral therapy in infants and children to treat HIV infection. Dosing based on either weight or body surface area has been approved by the U.S. Food and Drug Administration (FDA) but can be difficult to implement in resource-limited settings. The World Health Organization (WHO) has developed simplified weight band dosing for NVP, but it has not been critically evaluated. NVP pharmacokinetic data were combined from eight pediatric clinical trials (Pediatric AIDS Clinical Trials Group [PACTG] studies 245, 356, 366, 377, 403, 1056, and 1069 and Children with HIV in Africa Pharmacokinetics and Adherence of Simple Antiretroviral Regimens [CHAPAS]) representing subjects from multiple continents and across the pediatric age continuum. A population pharmacokinetic model was developed to characterize developmental changes in NVP disposition, identify potential sources of NVP pharmacokinetic variability, and assess various pediatric dosing strategies and their impact on NVP exposure. Age, CYP2B6 genotype, and ritonavir were independent predictors of oral NVP clearance. The Triomune fixed-dose tablet was an independent predictor of bioavailability compared to the liquid and other tablet formulations. Monte Carlo simulations of the final model were used to assess WHO weight band dosing recommendations. The final pharmacokinetic model indicated that WHO weight band dosing is likely to result in a percentage of children with NVP exposure within the target range similar to that obtained with FDA dosing. Weight band dosing of NVP proposed by the WHO has the potential to provide a simple and effective dosing strategy for resource limited settings.

Nevirapine pharmacokinetics and risk of rash and hepatitis among HIV-infected sub-Saharan African women

OBJECTIVES

To estimate nevirapine (NVP) pharmacokinetics and examine its association with rash and/or hepatotoxicity in women starting antiretroviral treatment in the AIDS Clinical Trials Group A5208/OCTANE study in Africa.

DESIGN

In HIV-infected, nonpregnant women with screening CD4 cell count less than 200 cells/μl randomized to NVP (twice daily, after 14-day once-daily lead-in period) and tenofovir/emtricitabine, single NVP blood samples were collected 14 and 28 days following randomization. Rash and hepatotoxicity that occurred during therapy, or within 7 days after the last dose of NVP, were defined as toxicity.

METHODS

NVP pharmacokinetics were modeled by population pharmacokinetic analysis. Individual Bayesian pharmacokinetic estimates were used to calculate clearance, 24-h area under the curve, and predicted plasma concentrations.

RESULTS

Median week 4 NVP clearance was 2 l/h. Among the 359 women, 194 (54%) developed a rash of any grade; 82 (23%) had grade 2+ and nine (3%) had grade 3+ rash. Median clearance was 1.7 l/h for participants exhibiting 3+ rash versus 2 l/h in women without 3+ rash (P = 0.046). The odds of developing 3+ rash was 50% higher for every 20% decrease in clearance (P = 0.046). NVP discontinuation due to rash/liver toxicity was significantly more common among women with pretreatment CD4 cell count more than 250 cells/μl (P = 0.003).

CONCLUSION

In this study, HIV-infected African women starting a NVP-based antiretroviral regimen had a lower NVP clearance compared to previous reports. Severe rash, but not hepatotoxicity, was associated with higher NVP exposure. Albeit observed in a small number of women, baseline CD4 cell count at least 250 cells/μl was significantly associated with NVP toxicity.

Influence of body weight on achieving indinavir concentrations within its therapeutic window in HIV-infected Thai patients receiving indinavir boosted with ritonavir

Indinavir boosted with ritonavir (IDV/r) dosing with 400/100 mg, twice daily, is preferred in Thai adults, but this dose can lead to concentrations close to the boundaries of its therapeutic window. The objectives of this analysis were to validate a population pharmacokinetic model to describe IDV/r concentrations in HIV-infected Thai patients and to investigate the impact of patient characteristics on achieving adequate IDV concentrations. IDV/r concentration data from 513 plasma samples were available. Population means and variances of pharmacokinetic parameters were estimated using a nonlinear mixed effects regression model (NONMEM Version VI). Monte Carlo simulations were performed to estimate the probability of achieving IDV concentrations within its therapeutic window. IDV/r pharmacokinetics were best described by a one-compartment model coupled with a single transit compartment absorption model. Body weight influenced indinavir apparent oral clearance and volume of distribution and allometric scaling significantly reduced the interindividual variability. Final population estimates (interindividual variability in percentage) of indinavir apparent oral clearance and volume of distribution were 21.3 L/h/70 kg (30%) and 90.7 L/70 kg (22%), respectively. Based on model simulations, the probability of achieving an IDV trough concentration greater than 0.1 mg/L was greater than 99% for 600/100 mg and greater than 98% for 400/100 mg, twice daily, in patients weighing 40 to 80 kg. However, the probability of achieving IDV concentrations associated with an increased risk of drug toxicity (greater than 10.0 mg/L) increased from 1% to 10% with 600/100 mg compared with less than 1% with 400/100 mg when body weight decreased from 80 to 40 kg. The validated model developed predicts that 400/100 mg of IDV/r, twice daily, provides indinavir concentrations within the recommended therapeutic window for the majority of patients. The risk of toxic drug concentrations increases rapidly with IDV/r dose of 600/100 mg for patients less than 50 kg and therapeutic drug monitoring of IDV concentrations would help to reduce the risk of IDV-induced nephrotoxicity.

Population pharmacokinetic-pharmacogenetic study of nevirapine in HIV-infected Cambodian patients

The aims of this ANRS12154 open-label, single-center, multiple-dose pharmacokinetic study were to characterize nevirapine pharmacokinetics in a Cambodian population of HIV-infected patients and to identify environmental and genetic factors of variability, focusing on the CYP2B6, CYP3A5, and ABCB1 (MDR1) genes. A total of 170 Cambodian HIV-infected patients were included. Nevirapine trough concentrations were measured after 18 and 36 months of starting antiretroviral treatment and in samples drawn during a dosing interval in a subset of 10 patients. All data were analyzed by nonlinear mixed-effects modeling. The effect of covariates was investigated using the population pharmacokinetic model. Patients carrying homozygous loss-of-function alleles CYP3A5 6986A>G, CYP2B6 516G>T, CYP2B6 1459C>T, and ABCB1 3435C>T represent 42.4%, 9.2%, 0%, and 18% of the population, respectively. The median nevirapine trough concentrations did not differ after 18 and 36 months of treatment (5,705 ng/ml [range, ≤50 to 13,871] and 5,709 ng/ml [range, ≤50 to 15,422], respectively). Interpatient and intrapatient variabilities of nevirapine apparent clearance were 28% and 17%, respectively. CYP2B6 516G>T and creatinine clearance were found to significantly affect nevirapine apparent clearance. The estimated nevirapine apparent clearances were 2.95 liters/h, 2.62 liters/h, and 1.86 liters/h for CYP2B6 516GG, CYP2B6 516GT, and CYP2B6 516TT genotypes, respectively. The impact of creatinine clearance was small. This study demonstrates that 95% of the patients had sustained nevirapine exposure well above the 3,000-ng/ml threshold. Nevirapine clearance was shown to be affected by CYP2B6 516G>T genetic polymorphism and creatinine clearance, although this explained only part of the interpatient variability, which remains low compared to that for other antiretroviral drugs.

Lack of pharmacokinetic interaction between amdoxovir and reduced- and standard-dose zidovudine in HIV-1-infected individuals

Amdoxovir (AMDX) inhibits HIV-1 containing the M184V/I mutation and is rapidly absorbed and deaminated to its active metabolite, beta-D-dioxolane guanosine (DXG). DXG is synergistic with zidovudine (ZDV) in HIV-1-infected primary human lymphocytes. A recent in silico pharmacokinetic (PK)/enzyme kinetic study suggested that ZDV at 200 mg twice a day (b.i.d.) may reduce toxicity without compromising efficacy relative to the standard 300-mg b.i.d. dose. Therefore, an intense PK clinical study was conducted using AMDX/placebo, with or without ZDV, in 24 subjects randomized to receive oral AMDX at 500 mg b.i.d., AMDX at 500 mg plus ZDV at 200 or 300 mg b.i.d., or ZDV at 200 or 300 mg b.i.d. for 10 days. Full plasma PK profiles were collected on days 1 and 10, and complete urine sampling was performed on day 9. Plasma and urine concentrations of AMDX, DXG, ZDV, and ZDV-5'-O-glucuronide (GZDV) were measured using a validated liquid chromatography-tandem mass spectrometry method. Data were analyzed using noncompartmental methods, and multiple comparisons were performed on the log-transformed parameters, at steady state. Coadministration of AMDX with ZDV did not significantly change either of the plasma PK parameters or percent recovery in the urine of AMDX, DXG, or ZDV/GZDV. Larger studies with AMDX/ZDV, with a longer duration, are warranted.

Efficacy of trichloroacetic acid in the treatment of anal intraepithelial neoplasia in HIV-positive and HIV-negative men who have sex with men

BACKGROUND

Anal intraepithelial neoplasia (AIN), particularly AIN 3 is a precursor to anal cancer. Most cases of AIN are intraanal, but few treatments for intraanal AIN are currently available. Topical 85% trichloroacetic acid (TCA) is an inexpensive method used to treat perianal condyloma, a form of AIN 1, but its efficacy to treat intraanal AIN as first-line therapy is unknown.

METHODS

Retrospective review of medical records was performed for all patients with AIN treated at the University of California San Francisco Anal Neoplasia Clinic with TCA as the first-line therapy from January 2000 to December 2004. Clearance was defined as the absence of AIN confirmed by high-resolution anoscopy and cytology after up to 4 TCA treatments.

RESULTS

Thirty-five HIV-positive men and 19 HIV-negative men met the enrollment criteria. In multivariate analysis, greater clearance was seen in patients 41-48 years of age versus >49 years [odds ratio (OR): 8.4, confidence interval (CI): 1.1 to 94, P: 0.04]. Among HIV-positive men, those with 2 or fewer lesions showed greater clearance (OR: 14.3, CI: 1.5 to 662, P: 0.01). 32% of patients with AIN 2/3 cleared to no lesions. On a per lesion basis, 73% of AIN 1 and 71% AIN 2/3 cleared to no lesion or AIN 1 or less, respectively.

CONCLUSIONS

Topical 85% TCA was safe and well tolerated. It was more effective in younger patients and among HIV-positive patients, those with 2 or fewer lesions. A high proportion of AIN 2/3 lesions responded to TCA treatment.

Response to zidovudine/didanosine-containing combination antiretroviral therapy among HIV-1 subtype C-infected adults in Botswana: two-year outcomes from a randomized clinical trial

BACKGROUND

Numerous national antiretroviral (ARV) treatment initiatives offering protease inhibitor-sparing combination antiretroviral therapy (cART) have recently commenced in southern Africa, the first of which began in Botswana in January 2002. Evaluation of the efficacy and tolerability of various protease inhibitor-sparing cART regimens requires intensive study in the region, as does investigation of the development of drug resistance and the optimal means of sustaining adherence. The "Tshepo" Study is the first large-scale, randomized, clinical trial that addresses these important issues among HIV-1 subtype C-infected ARV treatment-naive adults in southern Africa.

METHODS

The Tshepo Study is a completed, open-labeled, randomized study that enrolled 650 ARV-naive adults between December 2002 and 2004. The study is a 3 x 2 x 2 factorial design comparing the efficacy and tolerability among factors: (1) 3 combinations of nucleoside reverse transcriptase inhibitors (NRTIs): zidovudine (ZDV) + lamivudine (3TC), ZDV + didanosine (ddI), and stavudine (d4T) + 3TC; (2) 2 different nonnucleoside reverse transcriptase inhibitors (NNRTIs): nevirapine and efavirenz; and (3) 2 different adherence strategies: the current national "standard of care" versus an "intensified adherence strategy" incorporating a "community-based directly observed therapy." Study patients were stratified into 2 balanced CD4 T-cell count groups: less than 201 versus 201-350 cells per cubic millimeter with viral load greater than 55,000 copies per milliliter. Following Data Safety Monitoring Board recommendations in April 2006, ZDV/ddI-containing arms were discontinued due to inferiority in primary end point, namely, virologic failure with resistance. We report both overall data and pooled data from patients receiving ZDV/ddI- versus ZDV/3TC- and d4T/3TC-containing cART through April 1, 2006.

RESULTS

Four hundred fifty-one females (69.4%) and 199 males with a median age of 33.3 years were enrolled into the study. The median follow-up as of April 1, 2006, was 104 weeks, and loss to follow-up rate at 2 years was 4.1%. The median baseline CD4 T-cell count was 199 cells per cubic millimeter [interquartile ratio (IQR) 136-252], and the median plasma HIV-1 RNA level was 193,500 copies per milliliter (IQR 69-250, 472-500). The proportion of participants with virologic failure and genotypic resistance mutations was 11% in those receiving ZDV/ddI-based cART versus 2% in those receiving either ZDV/3TC- or d4T/3TC-based cART (P = 0.002). The median CD4 T-cell count increase at 1 year was 137 cells per cubic millimeter (IQR 74-223) and 199 cells per cubic millimeter (IQR 112-322) at 2 years with significantly lower gain in the ZDV/ddI arm. At 1 and 2 years, respectively, 92.0% and 88.8% of patients had an undetectable plasma HIV-1 RNA level (< or = 400 copies/mL). Kaplan-Meier survival estimates at 1 and 2 years were 96.6% and 95.4%. One hundred twenty patients (18.2%) had treatment-modifying toxicities, of which the most common were lipodystrophy, anemia, neutropenia, and Stevens-Johnson syndrome. There was a trend toward difference in time to treatment-modifying toxicity by pooled dual-NRTI combination and no difference in death rates.

CONCLUSIONS

The preliminary study results show overall excellent efficacy and tolerability of NNRTI-based cART among HIV-1 subtype C-infected adults. ZDV/ddI-containing cART, however, is inferior to the dual NRTIs d4T/3TC or ZDV/3TC when used with an NNRTI for first-line cART.

Risk factors for virological failure and subtherapeutic antiretroviral drug concentrations in HIV-positive adults treated in rural northwestern Uganda

BACKGROUND

Little is known about immunovirological treatment outcomes and adherence in HIV/AIDS patients on antiretroviral therapy (ART) treated using a simplified management approach in rural areas of developing countries, or about the main factors influencing those outcomes in clinical practice.

METHODS

Cross-sectional immunovirological, pharmacological, and adherence outcomes were evaluated in all patients alive and on fixed-dose ART combinations for 24 months, and in a random sample of those treated for 12 months. Risk factors for virological failure (>1,000 copies/ml) and subtherapeutic antiretroviral (ARV) concentrations were investigated with multiple logistic regression.

RESULTS

At 12 and 24 months of ART, 72% (n = 701) and 70% (n = 369) of patients, respectively, were alive and in care. About 8% and 38% of patients, respectively, were diagnosed with immunological failure; and 75% and 72% of patients, respectively, had undetectable HIV RNA (<400 copies/ml). Risk factors for virological failure (>1,000 copies/ml) were poor adherence, tuberculosis diagnosed after ART initiation, subtherapeutic NNRTI concentrations, general clinical symptoms, and lower weight than at baseline. About 14% of patients had low ARV plasma concentrations. Digestive symptoms and poor adherence to ART were risk factors for low ARV plasma concentrations.

CONCLUSION

Efforts to improve both access to care and patient management to achieve better immunological and virological outcomes on ART are necessary to maximize the duration of first-line therapy.

Considerations for the antiretroviral management of women in 2008

Clinicians should be familiar with sex-specific considerations when managing antiretroviral (ARV) treatment among women. Pregnancy is a critical influence on when to start treatment and what ARVs should be included in a regimen. Sex, pregnancy and hormonal contraceptive therapies can each influence ARV pharmacokinetic profiles. Women may be prone to have higher serum levels with selected ARV treatments, which may improve potency but also increase the risk for toxicities. Several studies have demonstrated that women do have higher frequencies of selected ARV-associated adverse events when compared with men. Although HIV treatment guidelines for nonpregnant women do not differ from men, clinicians should be aware of the high potential for certain ARV-related toxicities and follow suggestions in order to decrease the risk of side effects.

Development of an optimized dose for coformulation of zidovudine with drugs that select for the K65R mutation using a population pharmacokinetic and enzyme kinetic simulation model

In vitro selection studies and data from large genotype databases from clinical studies have demonstrated that tenofovir disoproxil fumarate and abacavir sulfate select for the K65R mutation in the human immunodeficiency virus type 1 polymerase region. Furthermore, other novel non-thymine nucleoside reverse transcriptase (RT) inhibitors also select for this mutation in vitro. Studies performed in vitro and in humans suggest that viruses containing the K65R mutation remained susceptible to zidovudine (ZDV) and other thymine nucleoside antiretroviral agents. Therefore, ZDV could be coformulated with these agents as a "resistance repellent" agent for the K65R mutation. The approved ZDV oral dose is 300 mg twice a day (b.i.d.) and is commonly associated with bone marrow toxicity thought to be secondary to ZDV-5'-monophosphate (ZDV-MP) accumulation. A simulation study was performed in silico to optimize the ZDV dose for b.i.d. administration with K65R-selecting antiretroviral agents in virtual subjects using the population pharmacokinetic and cellular enzyme kinetic parameters of ZDV. These simulations predicted that a reduction in the ZDV dose from 300 to 200 mg b.i.d. should produce similar amounts of ZDV-5'-triphosphate (ZDV-TP) associated with antiviral efficacy (>97% overlap) and reduced plasma ZDV and cellular amounts of ZDV-MP associated with toxicity. The simulations also predicted reduced peak and trough amounts of cellular ZDV-TP after treatment with 600 mg ZDV once a day (q.d.) rather than 300 or 200 mg ZDV b.i.d., indicating that q.d. dosing with ZDV should be avoided. These in silico predictions suggest that 200 mg ZDV b.i.d. is an efficacious and safe dose that could delay the emergence of the K65R mutation.

Population pharmacokinetics of nevirapine in combination with rifampicin-based short course chemotherapy in HIV- and tuberculosis-infected South African patients

OBJECTIVE

The aim was to develop a model to describe the population pharmacokinetics of nevirapine in South African human immunodeficiency virus (HIV)-infected patients who were taking nevirapine-based antiretroviral therapy concomitantly or in the absence of rifampicin-based tuberculosis therapy.

METHODS

Patients were divided into two groups: (1) patients receiving nevirapine-containing antiretroviral regimen (200 mg twice daily) and continuation phase rifampicin-containing tuberculosis therapy (n = 27) in whom blood samples were obtained before and not less than 14 days after they completed tuberculosis therapy; (2) patients without tuberculosis who were receiving a nevirapine-containing antiretroviral regimen for at least 3 weeks (n = 26). The population pharmacokinetics of nevirapine was described using nonlinear mixed effects modelling with NONMEM software. Based on the developed model, plasma concentration profiles after 300, 400 and 500 mg of nevirapine twice daily were simulated.

RESULTS

Concomitant administration of rifampicin increased nevirapine oral clearance (CL/F) by 37.4% and reduced the absorption rate constant (k(a)) by almost sixfold. Rifampicin reduced the nevirapine average minimum concentration by 39%. Simulated doses of 300 mg twice daily elevated nevirapine concentrations above subtherapeutic levels in most patients, with minimum exposure above the recommended maximum concentration. The area under the concentration-time curve of 12-hydroxynevirapine was not different in the presence of rifampicin. 2-, 3- and 8-Hydroxynevirapine were not detectable (LLOQ = 0.025 mg/L).

CONCLUSION

The developed model adequately describes nevirapine population pharmacokinetics in a South African population when taken with/and in the absence of rifampicin treatment. The simulations suggest that an increased dose of 300 mg twice daily would achieve adequate nevirapine concentrations in most patients during rifampicin-containing treatment for tuberculosis.

Factors Influencing Efavirenz and Nevirapine Plasma Concentration: Effect of Ethnicity, Weight and Co-Medication

Background

The aim of this study was to examine factors influencing plasma concentration of efavirenz and nevirapine.

Methods

Data from the Liverpool Therapeutic Drug Monitoring (TDM) registry were linked with the UK Collaborative HIV Cohort (CHIC) Study. For each patient, the first measurement of efavirenz (600 or 800 mg/day) or nevirapine (400 mg/day) plasma concentration was included. Linear regression was used to evaluate the association of dose, gender, age, weight, ethnicity and concomitant antiretroviral drugs or rifampicin with log-transformed drug concentration, adjusted for time since last intake.

Results

Data from 339 patients on efavirenz (34% black, 17% rifampicin) and 179 on nevirapine (27% black, 6% rifampicin) were included. Multivariable models revealed the following predictors for efavirenz concentration: black ethnicity (59% higher; P<0.001), weight (10% lower per additional 10 kg; P=0.002), 800 mg/day (52% higher; P=0.027), rifampicin (35% lower; P=0.039), and zidovudine (25% lower; P=0.010). Notably, without adjustment for other factors, patients on rifampicin had 48% higher efavirenz concentration, as these patients were mostly black and on 800 mg/day. For nevirapine the predictors were black ethnicity (39% higher; P=0.002), rifampicin (40% lower; P=0.002), protease inhibitor (28% higher; P=0.008) and tenofovir (22% higher; P=0.024).

Conclusions

We observed clear associations between ethnicity and concentrations of nevirapine and efavirenz. Our analyses confirm that concomitant rifampicin substantially decreases concentration of both efavirenz and nevirapine; however, for efavirenz this effect was more than counterbalanced by the effect of ethnicity and increased efavirenz dose. There was also an additional impact of weight, which should be considered when determining optimal dosage. Other associations from our analysis (between tenofovir or protease inhibitor and nevirapine, and zidovudine and efavirenz), require confirmation in formal pharmacokinetic studies.

Once- or twice-daily dosing of nevirapine in HIV-infected adults: a population pharmacokinetics approach

OBJECTIVES

The aim of this study was to develop and validate a population pharmacokinetic model for nevirapine in a population of HIV-infected adults and to evaluate the influence of nevirapine dosing regimen and patient characteristics on nevirapine trough concentration.

METHODS

HIV-infected adults receiving oral nevirapine for at least 4 weeks were included. A concentration-time profile was obtained for each patient, and nevirapine concentrations in plasma were determined by HPLC. Pharmacokinetic parameters, inter-individual variability and residual error were estimated using non-linear mixed effects modelling. The influence of patient characteristics on the pharmacokinetics of nevirapine was explored, and the predictive performance of the final model was evaluated in an external data set of observations.

RESULTS

Totals of 40 and 18 Caucasian patients were included in two data sets for model building and model validation, respectively. A mono-compartmental model with first-order absorption and elimination best described the pharmacokinetics of nevirapine. Body weight influenced oral clearance (CL/F) and volume of distribution (V/F). The estimated population pharmacokinetic parameters (inter-individual variability) for an individual weighing 70 kg were CL/F 2.95 L/h (24%), V/F 95.2 L (30%) and k(a) 1.8 h(-1) (96%). The final model predicted nevirapine concentrations in the external model-validation data set with no systematic bias and adequate precision. Bayesian estimates of nevirapine trough concentrations were lower when nevirapine was administered once instead of twice daily, and nearly half of the patients weighing 90 kg had drug concentrations <3.0 mg/L when nevirapine was dosed once daily.

CONCLUSIONS

A population model to describe the pharmacokinetics of nevirapine was developed and validated in HIV-infected patients. Body weight influenced CL/F and V/F. Based on Bayesian estimates of individual nevirapine concentrations, twice- instead of once-daily administration of nevirapine would be more optimal in patients weighing >70 kg.

Development of a population simulation model for HIV monotherapy virological outcomes using lamivudine

Current highly active antiretroviral therapy (HAART) requires the use of combinations of three drugs to minimize the early emergence of drug-resistant HIV strains. Therefore, long-term monotherapy data with new agents are unavailable. However, the development of computer models for Monte-Carlo-type simulations of antiviral monotherapy, which incorporate HIV infection dynamic distributions from previously studied populations, together with pharmacokinetics and pharmacodynamic parameters of the new agent, could serve as an important tool. The nucleoside lamivudine (3TC) was used as a representative drug to standardize an improved pharmacodynamic and infection dynamic monotherapy model. 3TC plasma concentration versus time profiles was used to drive the cellular accumulation of 3TC-triphosphate (TP) in primary human lymphocytes in the model, over a 16 week period. The fraction of HIV reverse transcription inhibited was calculated using the median inhibitory concentration and intracellular 3TC-TP levels. Virus loads and activated CD4+ T-cell counts were generated for 2,200 theoretical individuals and compared with the outcomes of an actual 3TC monotherapy trial at the same dose. Pharmacokinetic variance alone did not account for the interindividual HIV-load variability. However, selection of appropriate distributions of the various pharmacokinetic and infection dynamics parameters produced a similar range of virus load reductions to actual observations. Therefore, once parameter and variance distributions are standardized, this modelling approach could be helpful in planning clinical trials and predicting the antiviral contribution of each agent in a HAART modality.

Antiretroviral pharmacokinetic profile: a review of sex differences

BACKGROUND

Emerging evidence suggests that female sex may be associated with increased risk of developing antiretroviral toxicities. Although the mechanisms of sex-related antiretroviral pharmacodynamic differences remain poorly understood and may be multifactorial, they appear to be mediated through a common pathway of pharmacokinetic variability between the sexes.

OBJECTIVE

This article reviews sex differences in the pharmacokinetics of the major classes of antiretroviral drugs currently approved for HIV treatment by the US Food and Drug Administration, identifies knowledge gaps, and provides recommendations for future research directions.

METHODS

To identify pertinent articles for this review, the MEDLINE database was searched from 1990 to June 2006 using the terms sex, gender, antiretroviral therapy, ART, HAART, pharmacokinetics, pharmacodynamics, NRTI, NNRTI, and protease inhibitors. Search results were restricted to English language and human studies. The reference lists of identified articles were also used, as well as abstracts from relevant conferences. In addition, individual antiretroviral drugs were searched by sex/gender or by pharmacokinetics.

RESULTS

Current evidence, though limited, does suggest the existence of a sex disparity in antiretroviral pharmacokinetics, and such disparity has been shown to have pharmacodynamic implications for some drugs. Sex-mediated intracellular pharmaco-enhancement was associated with superior antiviral activities for the zidovudine and lamivudine members of the nucleoside reverse transcriptase inhibitor class. There appears to be divergent opinions about whether sex is a significant determinant of either nevirapine or efavirenz plasma concentrations. For certain protease inhibitors (PIs) (eg, saquinavir [SQV] and indinavir [IDV]), clinically significant relationships between sex differences in plasma drug concentrations and clinical outcomes have been observed. There appears to be a trend toward higher drug exposure in women than in men when PIs are boosted with ritonavir (RTV). Nelfinavir, the only PI that is currently administered unboosted with RTV, does not exhibit a sex difference in its plasma concentrations. Unboosted amprenavir exposure was lower in women compared with men. Sex differences in the pharmacokinetics of SQV and IDV were observed only in the setting of RTV boosting.

CONCLUSIONS

A common weakness in many studies addressing sex-based differences in the pharmacokinetics of antiretroviral drugs is the relatively small number of women participating. Many of these studies were retrospective in design, and some had limited pharmacokinetic parameters for comparison. Antiretroviral treatment trials should be designed with sufficient power (adequate female participation) to detect sex-based differences both in pharmacokinetics and in clinical response. Future studies should explore the molecular basis for sex-based differences in plasma drug concentrations and antiretroviral drug response. The roles of drug transporter proteins and cellular kinases, and the activities of metabolizing enzymes in mediating differential plasma and intracellular antiretroviral concentrations, should be further assessed.

Population pharmacokinetic analysis of lamivudine, stavudine and zidovudine in controlled HIV-infected patients on HAART

OBJECTIVE

This work aimed at building a population pharmacokinetic (PK) model for lamivudine (LMV), stavudine (STV) and zidovudine (ZDV), estimating their inter and intraindividual PK variability and investigating the influence of different covariates.

METHODS

Population PK of LMV, STV and ZDV was separately evaluated from plasma concentrations obtained in 54, 39 and 27 HIV1-infected patients, respectively, enrolled in the COPHAR1-ANRS102 trial. The primary objective of this trial was to study the pharmacokinetics of indinavir (IDV) and nelfinavir (NFV) in treated patients with a sustained virological response. Concentrations of nucleoside analogs (NA) were measured in plasma as a secondary objective. A one-compartment model with first-order elimination was used, with zero-order absorption for LMV and first-order absorption for STV and ZDV.

RESULTS

Mean parameters [interpatient variability in coefficient of variation (CV%)] of LMV, STV and ZDV were: oral volume of distribution (V/F) 145 l (52%), 24 l (81%) and 248 l (80%), oral clearance (Cl/F) 32 l/h, 16 l/h (74%) and 124 l/h (51%), respectively. For LMV, absorption duration (Ta) was 1.46 h (64%). For STV and ZDV, ka was 0.46 h(-1) and 2.9 h(-1), respectively. We found a systematic effect of combination with NFV vs. IDV. We found that intrapatient variability was greater than interpatient variability (except for STV) and greater than 55% for the three drugs.

CONCLUSION

This trial enabled the estimation of the population PK parameters of three NA in patients with a sustained virological response, and the median curves could be used as references for concentration-controlled strategies. We observed, as for the protease inhibitors, a great variability of PK parameters.

Lopinavir/Ritonavir pharmacokinetic profile: impact of sex and other covariates following a change from twice-daily to once-daily therapy

The aim of this study was to determine the impact of sex on the pharmacokinetics of lopinavir/ritonavir. Interaction between lopinavir/ritonavir and tenofovir was also evaluated. Steady-state plasma samples were obtained from virologically suppressed HIV-infected patients on lopinavir/ritonavir 800/200-mg soft gel capsule taken once daily. Drug assays were performed by high-performance liquid chromatography. Pharmacokinetic parameters estimated by noncompartmental method were reported as 90% confidence intervals (CIs) about the geometric mean ratio (GMR). There were 9 males and 11 females. No sex differences were observed in lopinavir/ritonavir pharmacokinetics profile. The GMR(sex) (women compared with men) for lopinavir area under the concentration-time curve (AUC(24)), maximum concentration (C(max)), and minimum concentration (C(min)) was 0.95 (90% CI, 0.70-1.29), 0.88 (90% CI, 0.67-1.15), and 1.27 (90% CI, 0.60-2.66), respectively. Similarly, the GMR(sex) for ritonavir AUC(24), C(max), and C(min) was 0.84 (90% CI, 0.57-1.24), 0.79 (90% CI, 0.50-1.22), and 1.02 (90% CI, 0.58-1.80), respectively. Tenofovir coadministration led to a reduction in lopinavir/ritonavir plasma exposure, giving a lopinavir GMR(tenofovir) for C(max) of 0.72 (90% CI, 0.57-0.93) and AUC(24) of 0.74 (90% CI, 0.56-0.98), respectively. No difference in lopinavir/ritonavir plasma concentrations between sexes was demonstrated in this study. However, tenofovir coadministration lowered lopinavir/ritonavir plasma exposure.

Neurotoxicity caused by didanosine on cultured dorsal root ganglion neurons

The purpose of the present study was to investigate whether didanosine (ddI) directly causes morphological and ultrastructural abnormalities of dorsal root ganglion (DRG) neurons in vitro. Dissociated DRG cells and organotypic DRG explants from embryonic 15-day-old Wistar rats were cultured for 3 days and then exposed to ddI (1 microg/ml, 5 microg/ml, 10 microg/ml, and 20 microg/ml) for another 3 days and 6 days, respectively. Neurons cultured continuously in medium served as normal controls. The diameter of the neuronal cell body and neurite length were measured in dissociated DRG cell cultures. Neuronal ultrastructural changes were observed in both culture models. ddI induced dose-dependent decreases in neurite number, length of the longest neurite in each neuron, and total neurite length per neuron in dissociated DRG cell cultures with 3 days treatment. There were no morphological changes seen in organotypic DRG cultures even with longer exposure time (6 days). But ddI induced ultrastructural changes in both culture models. Ultrastructural abnormalities included loss of cristae in mitochondria, clustering of microtubules and neurofilaments, accumulation of glycogen-like granules, and emergence of large dense particles between neurites or microtubules. Lysosome-like large particles emerged inconstantly in neurites. ddI induced a neurite retraction or neurite loss in a dose-dependent manner in dissociated DRG neurons, suggesting that ddI may partially contribute to developing peripheral neuropathy. Cytoskeletal rearrangement and ultrastructural abnormalities caused by ddI in both culture models may have a key role in neurite degeneration.

ADME pathway approach for pharmacogenetic studies of anti-HIV therapy

Pharmacogenetics holds promise in HIV treatment because of the complexity and potential toxicity of multidrug therapies that are prescribed for long periods. However, there has been limited success with the current approach where one or few candidate genes are examined for a limited number of allelic variants. A change in paradigm emerges from the availability of the HapMap, the wealth of data on less common genetic polymorphisms, and new genotyping technology. We present a comprehensive review of functional and putative functional variants in genes encoding absorption, distribution, metabolism and excretion (ADME) proteins relevant to HIV therapy. We propose an analytical array based on our review of the literature, web resources and use of bioinformatic analysis. We identified 126 genes with proven or potential role in HIV therapy. Variation in these genes can be characterized by 2428 SNPs (in Caucasians). On average, a gene is covered by 20 SNPs. This review compiles information for future analysis of the role of specific genes/variants in the exposure and response to antiretroviral therapy to generate a ranked list of new genetic variants for future studies.

Sex differences in pharmacokinetics and toxicity of antiretroviral therapy

Worldwide, the rate of new HIV infections continues to increase among women. Over the past 5 years there has been a growing focus on the clinical aspects of HIV infection among women. Historically, the majority of subjects enrolled in HIV clinical trials were male patients. Consequently, most knowledge about antiretroviral efficacy and toxicity has been derived from studies of predominately male subjects. More recently, results from clinical trials, especially those that have focused on HIV-infected female subjects, suggest that there may be clinically important gender-related differences in several aspects of HIV disease. These include, but are not limited to, differences in natural history, efficacy and safety of drug treatment. This chapter reviews current data on gender differences in antiretroviral pharmacokinetics and toxicity.

Once-daily nevirapine dosing: a pharmacokinetics, efficacy and safety review

In the context of attempts to simplify treatment regimens and enhance adherence, there is great interest in once-daily dosing regimens for the treatment of HIV-1 infection. Nevirapine has a long half-life and achieves high steady-state plasma concentrations relative to the concentration required to inhibit 50% viral replication in vitro (IC(50)) in patients. For this reason, it has been considered as a once-daily antiretroviral. Pharmacokinetic and efficacy data support the use of this dosing approach, but excess rash and lingering concerns over liver toxicity preclude use of once-daily dosed nevirapine at this time. Tolerance to high nevirapine concentrations may develop when dose escalation is used during initiation of therapy. It is theoretically possible that the benefits of once-daily dosing may be achieved without excess toxicity by switching to once-daily nevirapine following several months of twice-daily administration. This dosing strategy is currently under evaluation.

Population pharmacokinetics in geriatric psychiatry

Although geriatric patients are the major recipients of drugs, most research during drug development is conducted in healthy younger adults. Safe and effective drug therapy in the elderly requires an understanding of both drug disposition and response in older individuals. One of the major issues in studying the elderly relates to the ability to study a large number of people in a minimally invasive way. Population pharmacokinetics can be used to model drug concentrations from a large population of sparsely sampled individuals. Population pharmacokinetics characterizes both the interindividual (between-subject) and intraindividual (within-subject) variability, and can identify factors that contribute to pharmacokinetic and pharmacodynamic variability. Population pharmacokinetics can be used to aid in designing large clinical trials by simulating virtual data based on the study design. It can also be used to assess consistency of drug exposure and evaluate its effect on clinical outcome. This article reviews the methods used in pharmacokinetic modeling, as well as providing examples of population pharmacokinetic modeling, highlighting its application to geriatric psychiatry.

Genetic, ethnic, and gender differences in the pharmacokinetics of antiretroviral agents

Variable antiretroviral therapy (ART) drug response likely reflects the combined influence of environment, underlying disease, concurrent drugs, and genetics. Gender exerts modest or negligible effects on ART disposition, and it is expected to have limited clinical implication, although it should be accounted for in large population studies. Ethnic denominations have, with the notable exception of efavirenz, no clear influence on ART disposition. Exploration of genetic factors might offer a better comprehension to the largely unpredictable and unresolved variability in ART concentrations and related toxicity or treatment outcome. Despite the negative perception of genetic research among the general public, this type of investigation is now widely accepted by concerned parties: patients, relatives, and study volunteers.

Increased Body Mass Index Does Not Alter Response to Initial Highly Active Antiretroviral Therapy in HIV-1-Infected Patients

BACKGROUND

Body mass index (BMI) can influence drug metabolism, thus affecting efficacy and risk for toxicities. Hypothesizing that persons with an increased BMI and larger volumes of distribution may experience a suboptimal response to highly active antiretroviral therapy (HAART), we evaluated the effect of BMI on virologic and immunologic response in previously ART-naive patients initiating therapy.

METHODS

Using data from the HIV Outpatient Study, we analyzed the statistical association of BMI and other selected demographic variables with achieving an undetectable viral load and experiencing a CD4 cell count increase of more than 100 cell/microL after 3 to 9 months of therapy among antiretroviral-naive patients initiating HAART.

RESULTS

Among 711 patients included in analysis, 43% had a BMI of more than 25 (overweight-obese). Higher BMI was associated with being female, having black or Hispanic race/ethnicity, being heterosexual, and using injection drugs (all P<0.001). The patients in BMI groups did not differ significantly by baseline CD4 cell count or the duration of the initial HAART regimen. Although median baseline viral loads were significantly lower in obese participants (P=0.008), overweight or obese BMI did not significantly alter the likelihood of achieving an undetectable viral load and a CD4 cell count increase of more than 100 cells/microL compared with normal weight persons.

CONCLUSION

A substantial proportion of HIV-infected outpatients in this cohort were overweight or obese. Increased BMI was not associated with decreased virologic and immunologic responses to initial HAART. Responses were equivalent and within expected ranges between normal weight patients, overweight patients, and obese patients at 3 to 9 months of observation.

Pharmacology of current and promising nucleosides for the treatment of human immunodeficiency viruses

Nucleoside antiretroviral agents are chiral small molecules that have distinct advantages compared to other classes including long intracellular half-lives, low protein binding, sustained antiviral response when a dose is missed, and ease of chemical manufacture. They mimic natural nucleosides and target a unique but complex viral polymerase that is essential for viral replication. They remain the cornerstone of highly active antiretroviral therapy (HAART) and are usually combined with non-nucleoside reverse [corrected] transcriptase and protease inhibitors to provide powerful antiviral responses to prevent or delay the emergence of drug-resistant human immunodeficiency virus (HIV). The pharmacological and virological properties of a selected group of nucleoside analogs are described. Some of the newer nucleoside analogs have a high genetic barrier to resistance development. The lessons learned are that each nucleoside analog should be treated as a unique molecule since any structural modification, including a change in the enantiomeric form, can affect metabolism, pharmacokinetics, efficacy, toxicity and resistance profile.

Gender-specific considerations in the antiretroviral management of HIV-infected women

The vast majority of HIV-infected women are of childbearing potential, so issues surrounding reproduction and mother-to-child transmission of the virus are critical in the management of this population. Optimal antiretroviral management of pregnant women is a major global issue since antiretroviral regimens offered to pregnant women to decrease mother-to-child transmission in many countries are often not highly active against HIV. The subsequent emergence of resistant virus can have long-term sequelae for the mother, child, and ultimately, other exposed individuals. The efficacy of antiretroviral therapy appears similar in men and women, although women may experience higher toxicity profiles, which may, in turn, be related to the higher antiretroviral concentrations shown in pharmacokinetic studies. Further investigation into gender-related issues, including sex-associated antiretroviral toxicities, unique pharmacokinetic profiles and optimal antiretroviral management during pregnancy is needed.

Evaluation of antiretroviral therapy results in Blantyre, Malawi

We performed a cross sectional study to evaluate treatment results of the paying antiretroviral therapy clinic of Queen Elizabeth Central Hospital, Blantyre. The only antiretroviral therapy was a fixed drug combination of stavudine, lamivudine and nevirapine.

METHODS

Interviews, laboratory tests (CD4 count, viral load, nevirapine plasma levels, transaminases) and data extraction from files. 422 (59 %) of the patients who started antiretroviral therapy since 2000 were lost to follow up. The 176 patients enrolled in the study had good virological and excellent clinical treatment results. The most common side effect was peripheral neuropathy. Nevirapine plasma levels were remarkably high and associated with successful virological treatment results. Two simple adherence questions pertaining to the use of medication in the previous 8 days corresponded well with nevirapine levels. The most important reasons for non-adherence were shortage of drugs in the hospital pharmacy and personal financial constraints.

CONCLUSIONS

Many patients were lost to follow up.High nevirapine levels contributed to good therapy results in those studied.Simple adherence questions predicted sub-therapeutic nevirapine levels.Antiretroviral drug supply needs to be uninterrupted and free of charge, to prevent avoidable non-adherence.

Application and impact of population pharmacokinetics in the assessment of antiretroviral pharmacotherapy

Population pharmacokinetics has been an important technique used to explore and define relevant sources of variation in drug exposure and response in patient populations. This has been especially true in the area of antiretroviral therapy where the assurance of adequate and sustained drug exposure of multiple agents is highly correlated with therapeutic success. Population pharmacokinetic analyses across the four drug classes and 20 US FDA-approved products used to treat HIV have been published to date. The published reports were predominantly based on actual clinical trials conducted in HIV-infected patients with one or more agents administered. Modelling and simulation approaches have been used in the evaluation of antiretroviral agent outcomes incorporating problematic design and analysis factors such as sparse plasma sampling, data imbalance and censored data. Additional benefits of population modelling approaches applied to the investigation of antiretroviral agents include the ability to assess dosing compliance, understanding and quantifying drug-drug interactions in order to select dosing regimens and the screening of new drug candidates. Pharmacokinetic/pharmacodynamic models have been used to characterise the relationship between drug exposure and virological and immunological response, and to predict clinical outcome. These models offer the best opportunity for individualising and optimising patient therapy, particularly when adjusted for adherence/compliance. The impact of population pharmacokinetics in the area of antiretroviral therapy can be directly assessed by its role in the validation of surrogate markers such as viral RNA load, therapeutic drug monitoring and the management of individual patient outcomes via exposure-toxicity relationships. Each of these population pharmacokinetic outcomes has contributed to the current regulatory environment, specifically in the area of accelerated approval of new antiretroviral agents.

Weight related differences in the pharmacokinetics of abacavir in HIV-infected patients

AIM

To study the possible influence of patient characteristics on abacavir pharmacokinetics.

METHODS

A population pharmacokinetic model for abacavir was developed using data from 188 adult patients by the use of a nonlinear mixed effects modelling method performed with NONMEM.

RESULTS

Abacavir pharmacokinetics was well described by a two-compartment open model with linear absorption and elimination. Typical population estimates for the absorption rate constant (Ka), the apparent central distribution volume (Vc/F), the apparent peripheral distribution volume (Vp/F), the apparent intercompartmental clearance (Q/F) and the apparent plasma clearance (CL/F) were 1.8 h(-1), 75 l, 23.6 l, 10 l h(-1) and 47.5 l h(-1), respectively. Apparent plasma clearance was positively related to bodyweight. Individual Bayesian estimates of CL/F were used to calculate abacavir AUC. The latter decreased from 10.7 +/- 5.0 to 5.7 +/- 1.6 mgh l(-1) when bodyweight increased from 36 to 102 kg. This drop in abacavir exposure could lead to suboptimal treatment for the heaviest patients, as antiviral efficacy of abacavir is known to be related to its AUC. A 400 mg abacavir dose would be necessary to achieve adequate exposure to abacavir in patients weighing more than 60 kg.

CONCLUSIONS

The apparent plasma clearance of abacavir was positively related to bodyweight. The efficacy of the current recommended abacavir dosage for patients with high bodyweight should be evaluated in further studies.

Evaluation of antiretroviral therapy results in a resource-poor setting in Blantyre, Malawi

OBJECTIVE

To evaluate treatment results of the paying antiretroviral therapy (ART) clinic of Queen Elizabeth Central Hospital, a large public and teaching hospital in Blantyre, Malawi. The only ART was a fixed drug combination of stavudine, lamivudine and nevirapine.

METHODS

Cross sectional study with interviews, laboratory tests (CD4 count, viral load, nevirapine plasma levels, transaminases) and data extraction from files.

RESULTS

A total of 422 (59%) of the patients who started ART since 2000 were lost to follow-up. The 176 patients enrolled in the study had good virological and excellent clinical treatment results. The most common side effect was peripheral neuropathy. Nevirapine plasma levels were remarkably high and associated with successful virological treatment results. Two simple adherence questions pertaining to the use of medication in the previous 8 days corresponded well with nevirapine levels. The most important reasons for non-adherence were shortage of drugs in the hospital pharmacy and personal financial constraints.

CONCLUSIONS

(1) Many patients were lost to follow-up. (2) High nevirapine levels contributed to good therapy results in those studied. (3) Simple adherence questions predicted subtherapeutic nevirapine levels. (4) Antiretroviral drug supply needs to be uninterrupted and free of charge, to prevent avoidable non-adherence.

Are Adverse Events of Nevirapine and Efavirenz Related to Plasma Concentrations?

Objective

The relationships between adverse events (AEs) and plasma concentrations of nevirapine (NVP) and efavirenz (EFV) were investigated as part of the large, international, randomized 2NN study.

Methods

Treatment-naive, HIV-1-infected patients received NVP (once or twice daily), EFV or their combination, each in combination with lamivudine and stavudine. Blood samples were collected on day 3 and weeks 1, 2, 4, 24 and 48. Concentrations of NVP and EFV were quantitatively assessed by a validated HPLC assay. Individual Bayesian estimates of the area under the plasma concentration–time curve over 24 h (AUC24h), and minimum and maximum plasma concentrations (Cmin and Cmax) as measures for drug exposure of NVP and EFV, were generated using a previously developed population pharmacokinetic model. Pharmacokinetic parameters were compared for patients with and without central nervous system (CNS) and psychiatric AEs, hepatic events, liver enzyme elevations (LEEs) and rash. Furthermore, it was investigated whether a clear cut-off for a pharmacokinetic parameter could be identified above which the incidence of AEs was clearly increased. AEs were also related to demographic parameters and baseline characteristics.

Results

In total, from 1077 patients, NVP (3024 samples) and EFV (1694 samples) plasma concentrations and AE data (825 observations) were available. For all patients Cmin, Cmax and AUC24h were determined. When corrected for known covariates of gender, CD4 cell count at baseline, region, hepatitis coinfection and possible interactions between these factors, no significant associations between AEs and any tested exposure parameter of NVP was observed. Also, no target Cmin value, above which patients were at increased risk for AEs, could be established. On the other hand, geographical region, hepatitis coinfection, CD4 cell count and gender were found to be significantly related with the incidence of CNS and psychiatric AEs, hepatic events, LEEs and rash during the treatment with NVP. The occurrence of elevated liver enzymes during the first 6 weeks in the EFV-containing arm was significantly ( P=0.036) correlated to the exposure of EFV (Cmin). Only hepatitis coinfection impacted on LEEs during the first 6 weeks of treatment. With an EFV Cmin above 2.18 mg/l during the induction phase, patients were 4.4 (range 1.3–15.5) times more at risk for elevated liver enzymes. No other correlations between AEs and EFV pharmacokinetics or patient characteristics could be identified.

Conclusions

Pharmacokinetic parameters of NVP did not have a relationship to AEs in the 2NN trial when corrected for known covariates. The value of periodical drug monitoring of NVP as a way to prevent toxicity is therefore limited. Treating physicians should instead focus on factors that are more predictive of AEs (gender, CD4 count and hepatitis coinfection). High EFV Cmin levels resulted in elevated liver enzyme values during the first 6 weeks of treatment. Regular measurement of EFV levels and liver enzymes at the start of therapy may therefore be advised.