Integration of population pharmacokinetics and pharmacogenetics: an aid to optimal nevirapine dose selection in HIV-infected individuals

CYP2B6 Functional Variability in Drug Metabolism and Exposure Across Populations-Implication for Drug Safety, Dosing, and Individualized Therapy

Adverse drug reactions (ADRs) are one of the major causes of morbidity and mortality worldwide. It is well-known that individual genetic make-up is one of the causative factors of ADRs. Approximately 14 million single nucleotide polymorphisms (SNPs) are distributed throughout the entire human genome and every patient has a distinct genetic make-up which influences their response to drug therapy. Cytochrome P450 2B6 (CYP2B6) is involved in the metabolism of antiretroviral, antimalarial, anticancer, and antidepressant drugs. These drug classes are commonly in use worldwide and face specific population variability in side effects and dosing. Parts of this variability may be caused by single nucleotide polymorphisms (SNPs) in the CYP2B6 gene that are associated with altered protein expression and catalytic function. Population variability in the CYP2B6 gene leads to changes in drug metabolism which may result in adverse drug reactions or therapeutic failure. So far more than 30 non-synonymous variants in CYP2B6 gene have been reported. The occurrence of these variants show intra and interpopulation variability, thus affecting drug efficacy at individual and population level. Differences in disease conditions and affordability of drug therapy further explain why some individuals or populations are more exposed to CYP2B6 pharmacogenomics associated ADRs than others. Variabilities in drug efficacy associated with the pharmacogenomics of CYP2B6 have been reported in various populations. The aim of this review is to highlight reports from various ethnicities that emphasize on the relationship between CYP2B6 pharmacogenomics variability and the occurrence of adverse drug reactions. In vitro and in vivo studies evaluating the catalytic activity of CYP2B6 variants using various substrates will also be discussed. While implementation of pharmacogenomic testing for personalized drug therapy has made big progress, less data on pharmacogenetics of drug safety has been gained in terms of CYP2B6 substrates. Therefore, reviewing the existing evidence on population variability in CYP2B6 and ADR risk profiles suggests that, in addition to other factors, the knowledge on pharmacogenomics of CYP2B6 in patient treatment may be useful for the development of personalized medicine with regards to genotype-based prescription.

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).

Effect of patient genetics on etonogestrel pharmacokinetics when combined with efavirenz or nevirapine ART

BACKGROUND

We previously demonstrated that etonogestrel concentrations were 82% lower in women using etonogestrel contraceptive implants plus efavirenz-based ART compared with women not receiving ART.

OBJECTIVES

To investigate the genetic contribution to this previously observed drug-drug interaction through studying SNPs in genes known to be involved in efavirenz, nevirapine or etonogestrel metabolism in the same group of women.

PATIENTS AND METHODS

Here, we present a secondary analysis evaluating SNPs involved in efavirenz, nevirapine and etonogestrel metabolism and associated etonogestrel pharmacokinetics among 57 women, 19 not receiving ART (control group), 19 receiving efavirenz- (600 mg daily) based ART and 19 receiving nevirapine- (200 mg twice daily) based ART. Associations between patient genotype and etonogestrel pharmacokinetic parameters were determined through univariate and multivariate linear regression. This study was registered at clinicaltrials.gov (NCT02082652).

RESULTS

Within the control group, CYP2B6 983 T>C was associated with 27% higher etonogestrel Cmax and 28% higher AUC0-24weeks. In the efavirenz group CYP2B6 516 G>T was associated with 43% lower etonogestrel Cmin and 34% lower AUC0-24weeks. For participants receiving nevirapine, NR1I2 63396 C>T was associated with 39% lower etonogestrel Cmin and 37% lower AUC0-24weeks.

CONCLUSIONS

This study demonstrates the influence of pharmacogenetics on the extent of drug-drug interactions between etonogestrel and efavirenz- or nevirapine-based ART. Efavirenz plus the etonogestrel contraceptive implant results in a detrimental drug-drug interaction irrespective of patient genetics, which is worsened in women possessing variant alleles for these CYP2B6 SNPs.

Occurrence of CYP2B6 516G>T polymorphism in patients with ARV-associated hepatotoxicity

Background

Hepatic enzyme cytochrome P450 2B6 (CYP2B6) plays a role in the metabolism of efavirenz drugs. CYP2B6 516G>T variation showed an implication for HIV treatment.

Methods

CYP2B6 516G>T polymorphism was genotyped in a total 165 HIV patients that include 34 with and 131 without hepatotoxicity and 155 healthy individuals by the PCR‐RFLP.

Results

In patients with hepatotoxicity, the prevalence of CYP2B6 516TT genotype was higher as compared to healthy individuals (35.3% vs. 30.5%, OR = 1.74). Patients with hepatotoxicity using tobacco had a higher prevalence of genotypes CYP2B6 516GT, 516TT, 516GT+TT as compared to healthy individuals (28.57% vs. 25.93%; 57.14% vs. 29.63%; 85.71% vs. 55.56%). Likewise, hepatotoxicity in patients consuming alcohol showed higher distributions of CYP2B6 516GT, 516TT, 516GT+TT genotypes (57% vs. 25.93%; 42.86% vs. 33.33%; 71.43% vs. 59.26%). Nevirapine users with hepatotoxicity overrepresented genotypes CYP2B6 TT and 516GT+TT as compared to efavirenz users (47.83% vs. 45.45%, OR = 6.88, 65.22% vs. 54.55%, OR = 1.56). Similarly, in nevirapine +alcohol users with hepatotoxicity, the frequency of CYP2B6 516GT, 516GT+TT genotypes was higher than with nevirapine +alcohol nonusers (40.0% vs. 11.11%, OR = 8.00, 80.0% vs. 27.78%, OR = 4.00). In HIV patients, nevirapine users had higher frequency of CYP2B6 516GT, 516GT+TT genotypes as compared to efavirenz users (42.02% vs. 25.00%, OR = 2.53; 72.27% vs. 58.33%, OR = 1.86). Likewise, in HIV patients, genotypes CYP2B6 516GT, 516GT+TT were predominant with nevirapine +alcohol users as compared to nevirapine +alcohol nonusers (57.89% vs. 34.57%, OR = 2.46; 78.95% vs. 69.14%, OR = 1.67). In multivariate logistic regression, taking nevirapine had a protection for severity of ARV‐associated hepatotoxicity (OR = 0.23, p = 0.005).

Conclusions

No significant association was detected between CYP2B6 516G>T polymorphism and susceptibility to ARV‐associated hepatotoxicity.

Clinical and genetic factors associated with increased risk of severe liver toxicity in a monocentric cohort of HIV positive patients receiving nevirapine-based antiretroviral therapy

Background

Nevirapine has been used as antiretroviral agent since early ‘90. Although nevirapine is not currently recommended in initial anti-HIV regimens, its use remains consistent in a certain number of HIV-1-positive subjects. Thus, our aim was to determine clinical and genetic factors involved in the development of severe nevirapine induced liver toxicity.

Methods

We retrospectively analyzed all HIV positive patients who were followed at the Infectious Diseases Unit, DIBIC Luigi Sacco, University of Milan from May 2011 to December 2015. All patients treated with nevirapine who underwent a genotyping for the functional variants mapping into ABCB1, CYP2B6, CYP3A4 and CYP3A5 genes were included in the analysis. Severe hepatotoxicity was defined as ACTG grade 3–4 AST/ALT increase during the first three months of nevirapine treatment. The causality assessment between NVP exposure and drug-induced liver injury was performed by using the updated Roussel Uclaf Causality Assessment Methods. Hardy Weinberg equilibrium was tested by χ² test. A multivariable logistic regression model was constructed using a backward elimination method.

Results

Three hundred and sixty-two patients were included in the analysis, of which 8 (2.2%) experienced a severe liver toxicity. We observed no differences between patients with and without liver toxicity as regards gender, ethnicity, age and immune-virological status. A higher prevalence of HCV coinfection (75.0% vs 30.2%; p = .0013) and higher baseline AST (58 IU/L vs 26 IU/L; p = 0.041) and ALT (82 IU/L vs 27 IU/L; p = 0.047) median levels were observed in patients with liver toxicity vs those without toxicity. The genotypes CT/TT at ABCB1 rs1045642 single nucleotide polymorphism (SNP), showed a protective effect for liver toxicity when compared with genotype CC (OR = 0.18, 95%CI 0.04–0.76; p = 0.020) in univariate analysis. In the multivariate model, HCV coinfection was independently associated with higher risk of developing liver toxicity (aOR = 8.00, 95%CI 1.27–50.29; p = 0.027), whereas ABCB1 rs1045642 CT/TT genotypes (aOR = 0.10, 95%CI 0.02–0.47; p = 0.004) was associated with a lower risk.

Conclusions

According to our findings HCV coinfection and ABCB1 rs1045642 SNP represent independent determinants of severe liver toxicity related to nevirapine. This genetic evaluation could be included as toxicity assessment in HIV-1-positive subjects treated with nevirapine.

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.

Pharmacogenetic associations with cytochrome P450 in antiretroviral therapy: what does the future hold?

INTRODUCTION

Several antiretroviral drugs used to treat infection with the human immunodeficiency virus (HIV) are substrates of enzymes belonging to the cytochrome P450 (CYP) superfamily, which are polymorphically expressed. It may therefore be useful to take into account the genetic variation in these enzymes to predict the likelihood of anti-HIV treatment success, toxicity and the potential for drug-drug interactions. Areas covered: In this manuscript, the authors discuss the current state of knowledge regarding pharmacogenetic associations between CYP and all major antiretrovirals, as well as the importance of these associations. Expert opinion: While many pharmacogenetic associations for CYP have been described in the literature, replication studies are sometimes lacking. The implementation of this knowledge in clinical practice also remains difficult. Further efforts are required both to expand this field of knowledge and to enable its use in everyday clinical practice.

Precision medicine for HIV: where are we?

To date, antiretroviral therapy is highly effective in HIV-affected patients, but the individualization of such a life-long therapy may be advised. This review briefly summarizes the main factors involved in the potential personalization of antiretroviral treatment. Relevant articles in English were identified by PubMed and recent congresses’ abstracts. Foremost influences concerning pharmacodynamics, therapeutic drug monitoring, pharmacogenetics, comorbidities, immune recovery and viral characteristics affecting the healthcare of HIV-positive patients are listed here. Furthermore, pharmacoeconomic aspects are mentioned. Applying pharmacokinetic and pharmacogenetic knowledge may be informative and guide the better choice of treatment in order to achieve long-term efficacy and avoid adverse events. Randomized investigations of the clinical relevance of tailored antiretroviral regimens are needed in order to obtain a better management of HIV/AIDS-affected patients.

Genetic Polymorphisms Affecting the Pharmacokinetics of Antiretroviral Drugs

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Assessment of Nevirapine Prophylactic and Therapeutic Dosing Regimens for Neonates

BACKGROUND

Nevirapine (NVP) is a key component of antiretroviral prophylaxis and treatment for neonates. We evaluated current World Health Organization (WHO) weight-band NVP prophylactic dosing recommendations and investigated optimal therapeutic NVP dosing for neonates.

METHODS

The PHPT-5 study in Thailand assessed the efficacy of "Perinatal Antiretroviral Intensification" to prevent mother-to-child transmission of HIV in women with <8 weeks of antiretroviral treatment before delivery (NCT01511237). Infants received a 2-week course of zidovudine/lamivudine/NVP (NVP syrup/once daily: 2 mg/kg for 7 days; then 4 mg/kg for 7 days). Infant samples were assessed during the first 2 weeks of life. NVP population pharmacokinetics (PK) parameters were estimated using nonlinear mixed-effects models. Simulations were performed to estimate the probability of achieving target NVP trough concentrations for prophylaxis (>0.10 mg/L) and for therapeutic efficacy (>3.0 mg/L) using different infant dosing strategies.

RESULTS

Sixty infants (55% male) were included. At birth, median (range) weight was 2.9 (2.3-3.6) kg. NVP concentrations were best described by a 1-compartment PK model. Infant weight and postnatal age influenced NVP PK parameters. Based on simulations for a 3-kg infant, ≥92% would have an NVP trough >0.1 mg/L after 48 hours through 2 weeks using the PHPT-5 and WHO-dosing regimens. For NVP-based therapy, a 6-mg/kg twice daily dose produced a trough >3.0 mg/L in 87% of infants at 48 hours and 80% at 2 weeks.

CONCLUSION

WHO weight-band prophylactic guidelines achieved target concentrations. Starting NVP 6 mg/kg twice daily from birth is expected to achieve therapeutic concentrations during the first 2 weeks of life.

Efficacy and safety of switching from nevirapine immediate-release twice daily to nevirapine extended-release once daily in virologically suppressed HIV-infected patients: a retrospective cohort study in Taiwan

Background

Whether the non-inferior efficacy and safety results of switching virologically suppressed HIV-1-infected patients from nevirapine immediate-release (NVP-IR) to NVP extended-release (NVP-XR) demonstrated in the TRANxITION study conducted in Europe and North America are also applicable to virologically suppressed HIV-infected Taiwanese patients remains unknown. We evaluated the comparative safety and efficacy of continuing NVP-IR versus switching to NVP-XR in virologically suppressed HIV-infected Taiwanese adults receiving combined antiretroviral therapy (cART) regimens.

Methods

We conducted a retrospective cohort study at Kaohsiung Veterans General Hospital from April 1, 2013, to March 31, 2015. Eighty-four virologically suppressed HIV-infected adults receiving NVP-IR cART were split into two groups: those continuing with NVP-IR (n = 49) and those being switched to NVP-XR (n = 35). Demographic characteristics, clinical variables, and laboratory findings were compared. Therapeutic drug monitoring of steady-state plasma NVP concentrations and genotype analysis of CYP2B6 516 were also performed in 22 participants. The primary endpoint was continued virological suppression at the end of the study. Secondary endpoints were time to loss of virological response and adverse events.

Results

During a mean follow-up of 18.4 months, the NVP-XR group demonstrated similar success at maintaining virological response compared with the NVP-IR group (82.9% vs. 85.7%; P = 0.72). Cox regression analysis indicated that there were no significant differences between NVP regimens for time to loss of virological response (hazard ratio: 0.940; P = 0.754). Furthermore, there were no significant differences in adverse events between these two groups. In the 22 participants, there was a non-significantly lower level of steady-state plasma NVP concentrations in the NVP-XR group than in NVP-IR recipients (5145.0 ng/mL vs. 6775.0 ng/mL; P = 0.267). The prevalence of CYP2B6 516 GT was 86.6%, and there was no significant difference in the distribution of CYP2B6 516 between these two groups.

Conclusions

We found that switching from NVP-IR to NVP-XR appeared to have similar safety and efficacy compared with continuing NVP-IR among virologically suppressed, HIV-infected Taiwanese patients. Our finding of higher C_trough levels in both groups compared with other studies conducted in Caucasian populations and the high prevalence of CYP2B6 516 GT requires further investigation in a larger Taiwanese cohort.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-017-2371-3) contains supplementary material, which is available to authorized users.

[The Competence Network for HIV/AIDS. Data, Samples, Facts]

BACKGROUND

With funding for the Competence Networks in Medicine from the Federal Ministry of Education and Research, the Competence Network for HIV/AIDS (KompNet HIV/AIDS) was established as an interdisciplinary research association. Essential working groups were incorporated all over Germany, which are active in clinical and basic HIV/AIDS research.

OBJECTIVES

After successful establishment, providing research infrastructure for national and international cooperation in the field of HIV/AIDS was the focus of the network. By bringing together research activities, preconditions are created for improving HIV infection treatment and increasing life expectancy of HIV-infected patients.

MATERIALS AND METHODS

The members of KompNet HIV/AIDS are HIV experts from university clinics, HIV physicians, patient representatives, as well as national reference centers. As a scientific research basis, the network established an HIV patient cohort. Clinical and sociodemographic data of HIV patients were documented biannually and complemented by serum and DNA-samples collected twice per year. Furthermore, a child cohort was set up.

RESULTS AND CONCLUSION

Within the KompNet HIV/AIDS, a research infrastructure for HIV was established for internal, external as well international scientists. Within the HIV cohort a total of 16,500 patients are documented. The associated biobank comprises ~ 56,000 serum samples and ~ 16,000 DNA samples. The child cohort consists of 647 HIV-exposed and 230 infected children. The KompNet HIV/AIDS cohorts became an important partner in several international collaborations. Nevertheless, the maintenance of such infrastructures without public funding is a challenge.

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.

Individualization of antiretroviral therapy--pharmacogenomic aspect

Combination therapy with three drug regimens for human immunodeficiency virus (HIV) infection significantly suppresses the viral replication. However, this therapeutic impact is restricted by adverse drug events and response in terms of short and long term efficacy. There are multiple factors involved in different responses to antiretrovirals (ARVs) such as age, body weight, disease status, diet and heredity. Pharmacogenomics deals with individual genetic make-up and its role in drug efficacy and toxicity. In depth genetic research has provided evidence to predict the risk of developing certain toxicities for which personalized screening and surveillance protocols may be developed to prevent side effects. Here we describe the use of pharmacogenomics for optimal use of HAART (highly active antiretroviral therapy).

Insights into CYP2B6-mediated drug-drug interactions

Mounting evidence demonstrates that CYP2B6 plays a much larger role in human drug metabolism than was previously believed. The discovery of multiple important substrates of CYP2B6 as well as polymorphic differences has sparked increasing interest in the genetic and xenobiotic factors contributing to the expression and function of the enzyme. The expression of CYP2B6 is regulated primarily by the xenobiotic receptors constitutive androstane receptor (CAR) and pregnane X receptor (PXR) in the liver. In addition to CYP2B6, these receptors also mediate the inductive expression of CYP3A4, and a number of important phase II enzymes and drug transporters. CYP2B6 has been demonstrated to play a role in the metabolism of 2%–10% of clinically used drugs including widely used antineoplastic agents cyclophosphamide and ifosfamide, anesthetics propofol and ketamine, synthetic opioids pethidine and methadone, and the antiretrovirals nevirapine and efavirenz, among others. Significant inter-individual variability in the expression and function of the human CYP2B6 gene exists and can result in altered clinical outcomes in patients receiving treatment with CYP2B6-substrate drugs. These variances arise from a number of sources including genetic polymorphism, and xenobiotic intervention. In this review, we will provide an overview of the key players in CYP2B6 expression and function and highlight recent advances made in assessing clinical ramifications of important CYP2B6-mediated drug–drug interactions.

Effects of CYP2B6 and CYP1A2 Genetic Variation on Nevirapine Plasma Concentration and Pharmacodynamics as Measured by CD4 Cell Count in Zimbabwean HIV-Infected Patients

The extremely high prevalence of HIV/AIDS in sub-Saharan Africa and limitations of current antiretroviral medicines demand new tools to optimize therapy such as pharmacogenomics for person-to-person variations. African populations exhibit greater genetic diversity than other world populations, thus making it difficult to extrapolate findings from one population to another. Nevirapine, an antiretroviral medicine, displays large plasma concentration variability which adversely impacts therapeutic virological response. This study, therefore, aimed to identify sources of variability in nevirapine pharmacokinetics and pharmacodynamics, focusing on genetic variation in CYP2B6 and CYP1A2. Using a cross-sectional study design, 118 HIV-infected adult Zimbabwean patients on nevirapine-containing highly active antiretroviral therapy (HAART) were characterized for three key functional single nucleotide polymorphisms (SNPs), CYP2B6 c.516G>T (rs3745274), CYP2B6 c.983T>C (rs28399499), and CYP1A2 g.-163C>A (rs762551). We investigated whether genotypes at these loci were associated with nevirapine plasma concentration, a therapeutic biomarker, and CD4 cell count, a biomarker of disease progression. CYP2B6 and CYP1A2 were chosen as the candidate genes based on reports in literature, as well as their prominence in the metabolism of efavirenz, a drug in the same class with nevirapine. Nevirapine plasma concentration was determined using LC-MS/MS. The mean nevirapine concentration for CYP2B6 c.516T/T genotype differed significantly from that of 516G/G (p < 0.001) and 516G/T (p < 0.01) genotypes, respectively. There were also significant differences in mean nevirapine concentration between CYP2B6 c.983T > C genotypes (p = 0.04). Importantly, the CYP1A2 g.-163C>A SNP was significantly associated with the pharmacodynamics endpoint, the CD4 cell count (p = 0.012). Variant allele frequencies for the three SNPs observed in this Zimbabwean group were similar to other African population groups but different to observations among Caucasian and Asian populations. We conclude that CYP2B6 c.516G>T and CYP2B6 c.983T>C could be important sources of nevirapine pharmacokinetic variability that could be considered for dosage optimization, while CYP1A2 g.-163C>A seems to be associated with HIV disease progression. These inter- and intra-population pharmacokinetic and pharmacodynamics differences suggest that a single prescribed dosage may not be appropriate for the treatment of disease. Further research into a personalized nevirapine regimen is required.

Population pharmacokinetics of nevirapine in Malaysian HIV patients: a non-parametric approach

AIMS

Nevirapine is the first non-nucleoside reverse-transcriptase inhibitor approved and is widely used in combination therapy to treat HIV-1 infection. The pharmacokinetics of nevirapine was extensively studied in various populations with a parametric approach. Hence, this study was aimed to determine population pharmacokinetic parameters in Malaysian HIV-infected patients with a non-parametric approach which allows detection of outliers or non-normal distribution contrary to the parametric approach.

METHODS

Nevirapine population pharmacokinetics was modelled with Pmetrics. A total of 708 observations from 112 patients were included in the model building and validation analysis. Evaluation of the model was based on a visual inspection of observed versus predicted (population and individual) concentrations and plots weighted residual error versus concentrations. Accuracy and robustness of the model were evaluated by visual predictive check (VPC). The median parameters' estimates obtained from the final model were used to predict individual nevirapine plasma area-under-curve (AUC) in the validation dataset. The Bland-Altman plot was used to compare the AUC predicted with trapezoidal AUC.

RESULTS

The median nevirapine clearance was of 2.92 L/h, the median rate of absorption was 2.55/h and the volume of distribution was 78.23 L. Nevirapine pharmacokinetics were best described by one-compartmental with first-order absorption model and a lag-time. Weighted residuals for the model selected were homogenously distributed over the concentration and time range. The developed model adequately estimated AUC.

CONCLUSIONS

In conclusion, a model to describe the pharmacokinetics of nevirapine was developed. The developed model adequately describes nevirapine population pharmacokinetics in HIV-infected patients in Malaysia.

A pharmacist’s role in the individualization of treatment of HIV patients

The pharmacological treatment of HIV is complex and varies considerably among patients, as does the response of patients to therapy, requiring treatment plans that are closely tailored to individual needs. Pharmacists can take an active role in individualizing care by employing their knowledge of pharmacokinetics and pharmacogenetics and by interacting directly with patients in counseling sessions. These strategies promote the following: maintenance of plasma concentrations of antiretroviral agents within therapeutic ranges, prediction of pharmacological response of patients with certain genetic characteristics, and clinical control of HIV through the correct use of antiretroviral treatments. Together, these strategies can be used to tailor antiretroviral therapy to individual patients, thus improving treatment efficacy and safety.

An Expanded Analysis of Pharmacogenetics Determinants of Efavirenz Response that Includes 3'-UTR Single Nucleotide Polymorphisms among Black South African HIV/AIDS Patients

Introduction: Efavirenz (EFV) is a non-nucleoside reverse transcriptase inhibitor prescribed as part of first-line highly active antiretroviral therapy (HAART) in South Africa. Despite administration of fixed doses of EFV, inter-individual variability in plasma concentrations has been reported. Poor treatment outcomes such as development of adverse drug reactions or treatment failure have been linked to EFV plasma concentrations outside the therapeutic range (1–4 μg/mL) in some studies. The drug metabolizing enzyme (DME), CYP2B6, is primarily responsible for EFV metabolism with minor contributions by CYP1A2, CYP2A6, CYP3A4, CYP3A5, and UGT2B7. DME coding genes are also regulated by microRNAs through targeting the 3′-untranslated region. Expanded analysis of 30 single nucleotide polymorphisms (SNPs), including those in the 3′-UTR, was performed to identify pharmacogenetics determinants of EFV plasma concentrations in addition to CYP2B6 c.516G>T and c.983T>C SNPs.

Methods: SNPs in CYP1A2, CYP2B6, UGT2B7, and NR1I2 (PXR) were selected for genotyping among 222 Bantu-speaking South African HIV-infected patients receiving EFV-containing HAART. This study is a continuation of earlier pharmacogenetics studies emphasizing the role of genetic variation in the 3′-UTR of genes which products are either pharmacokinetic or pharmacodynamic targets of EFV.

Results: Despite evaluating thirty SNPs, CYP2B6 c.516G>T and c.983T>C SNPs remain the most prominent predictors of EFV plasma concentration.

Conclusion: We have shown that CYP2B6 c.516G>T and c.983T>C SNPs are the most important predictors of EFV plasma concentration after taking into account all other SNPs, including genetic variation in the 3′-UTR, and variables affecting EFV metabolism.

Pharmacogenetics of non-nucleoside reverse transcriptase inhibitors (NNRTIs) in resource-limited settings: Influence on antiretroviral therapy response and concomitant anti-tubercular, antimalarial and contraceptive treatments

The burden of human immunodeficiency virus (HIV) is mainly concentrated to resources-limited countries where the response to available antiretroviral therapy is often limited by the occurrence of toxicity or by the emergence of HIV drug resistance. Efavirenz and nevirapine are the antiretroviral drugs most prescribed in resources-limited countries as part of antiretroviral combination therapy. Their metabolism and conjugation are largely influenced by enzymatic genetic polymorphisms. The genetic variability of their metabolism could be associated to different metabolic phenotypes causing reduced patients' adherence because of toxicity or drug-drug interactions with concomitant therapies. The purpose of this review is to summarize published evidence on pharmacogenetic and pharmacokinetic aspects related to efavirenz and nevirapine, the influence of concomitant anti-tubercular, anti-malarial or contraceptive treatments, and the impact of human genetic variation and drug-drug interaction on the virologic and immunologic response to antiretroviral therapy in resources-limited countries.

Use of in vitro to in vivo extrapolation to predict the optimal strategy for patients switching from efavirenz to maraviroc or nevirapine

BACKGROUND AND OBJECTIVES

In clinical practice, antiretroviral regimens are often interrupted or modified for intolerance and toxicity. The objective of this study was to develop an in vitro to in vivo extrapolation (IVIVE) approach to describe the interaction when efavirenz is switched to either maraviroc or nevirapine and to test different switching scenarios to identify the best strategy.

METHODS

In vitro data describing the chemical and absorption, tissue distribution, metabolism and excretion (ADME) characteristics of efavirenz, maraviroc and nevirapine were obtained from the literature, and used to simulate plasma exposures of these drugs using the Simcyp Population-Based Simulator. The predicted maraviroc and nevirapine exposures were compared with data from clinical studies evaluating their exposures following a switch from efavirenz.

RESULTS

Model predictions for maraviroc and nevirapine exposure were in agreement with observed data. The simulations suggest that the waning efavirenz induction effect following discontinuation necessitated increasing maraviroc to 600 mg twice daily for 1 week after efavirenz cessation. Alternatively, adequate exposure of maraviroc was shown with a dose of 450 mg for 2 weeks. Efavirenz waning induction did not affect nevirapine exposure.

CONCLUSION

IVIVE modelling successfully predicted patient drug exposure. This modelling technique is able to inform the design of clinical studies, and allows assessment of pragmatic dosing strategies under complex therapeutic scenarios.

Class-specific relative genetic contribution for key antiretroviral drugs

OBJECTIVES

Antiretroviral pharmacokinetics is defined by numerous factors affecting absorption, distribution, metabolism and elimination. Biological processes underpinning drug distribution are only partially characterized and multiple genetic factors generate cumulative or antagonistic interactions, which complicates the implementation of pharmacogenetic markers. The aim of this study was to assess the degree to which heredity influences pharmacokinetics through the quantification of the relative genetic contribution (rGC) for key antiretrovirals.

METHODS

A total of 407 patients receiving lopinavir/ritonavir, atazanavir/ritonavir, atazanavir, efavirenz, nevirapine, etravirine, maraviroc, tenofovir or raltegravir were included. Intra-patient variability (SDw) and inter-patient (SDb) variability were measured in patients with plasma concentrations available from more than two visits. The rGC was calculated using the following equation: 1 - (1 / F) where F = SDb(2) / SDw(2).

RESULTS

Mean (95% CI) rGC was calculated to be 0.81 (0.72-0.88) for efavirenz, 0.74 (0.61-0.84) for nevirapine, 0.67 (0.49-0.78) for etravirine, 0.65 (0.41-0.79) for tenofovir, 0.59 (0.38-0.74) for atazanavir, 0.47 (0.27-0.60) for atazanavir/ritonavir, 0.36 (0.01-0.48) for maraviroc, 0.15 (0.01-0.44) for lopinavir/ritonavir and 0 (0-0.33) for raltegravir.

CONCLUSIONS

The rank order for genetic contribution to variability in plasma concentrations for the study drugs was efavirenz > nevirapine > etravirine > tenofovir > atazanavir > atazanavir/ritonavir > maraviroc > lopinavir/ritonavir > raltegravir, indicating that class-specific differences exist. The rGC strategy represents a useful tool to rationalize future investigations as drugs with higher rGC scores may represent better candidates for pharmacogenetic-pharmacokinetic studies.

Cytochrome P450 2B6 genetic variants are associated with plasma nevirapine levels and clinical response in HIV-1 infected Kenyan women: a prospective cohort study

Background

Polymorphisms in cytochrome P450 2B6 (CYP2B6) affect the steady state plasma concentration of nevirapine. CYP2B6 516G>T and 983T>C are common in African populations, but data on their influence on plasma nevirapine concentration and clinical response in African women are limited. We investigated the impact of CYP 516G>T and 983T>C on plasma nevirapine concentration and clinical outcomes in a prospective cohort study of HIV-infected Kenyan women.

Methods

Study subjects were 66 HIV-1-seropositive women taking nevirapine-based antiretroviral therapy. Plasma collected at week 12 was analyzed for nevirapine concentration by high performance liquid chromatography. Baseline samples were genotyped for CYP2B6 516G>T and 983T>C single nucleotide polymorphisms by real-time polymerase chain reaction. CD4 cell count, plasma viral load, and genotypic drug resistance in plasma and genital secretions were assessed at baseline and during follow up. We evaluated the effect of each genotype on plasma nevirapine concentration at week 12 and on change in CD4 cell count at months 3, 6 and 12. Associations between plasma nevirapine concentration and clinical outcomes were analyzed by logistic or linear regression.

Results

Women with CYP2B6 516TT genotype (n=9) had higher mean nevirapine plasma levels (14.33 μg/mL) compared to those with heterozygous 516GT (9.18 μg/mL; n=25) and wild- type 516GG (7.95 μg/mL; n=32) genotypes (P=0.01). Women heterozygous for the CYP2B6 983TC genotype (n=13) had higher mean nevirapine plasma levels (12.94 μg/mL), compared to women with the homozygous 983TT (8.35 μg/mL; n=53) genotype (P=0.007). In Generalized Estimating Equation analysis, plasma nevirapine levels predicted greater change in CD4 cell count after ART initiation (adjusted beta 119.4 cells/μL, 95% CI, 27.3–211.5 cells/μL, P=0.01). The CYP2B6 983TT genotype also predicted greater change in CD4 cell count (adjusted beta 68.6 cells/μL, 95% CI, 3.9–133.4 cells/μL, P=0.04). We found no associations between CYP2B6 genotypes and virologic response or toxicity.

Conclusions

CYP2B6 516G>T and CYP2B6 983T>C genotypes were strongly associated with plasma nevirapine concentration, which predicted immunologic response in women on nevirapine-based antiretroviral therapy. These data support continued work on the potential utility of human genetic testing to inform nevirapine dosage optimization for individual patients.

Evaluation of adherence measures of antiretroviral prophylaxis in HIV exposed infants in the first 6 weeks of life

BACKGROUND

Adherence to an antiretroviral regimen is imperative for treatment success in both HIV infected adults and children. Likewise, adherence to antiretroviral prophylaxis is critical in HIV prevention. Studies on pediatric adherence are limited, particularly the prophylactic use of antiretroviral drugs and treatment adherence in very young infants. The HIV Prevention Trials Network (HPTN) 046 study (Clinical Trial Registration NCT00074412) determined the safety and efficacy of an extended regimen of nevirapine suspension in infants born to HIV-1 infected women for the prevention of vertical HIV transmission during breastfeeding. As per protocol, adherence to nevirapine prophylaxis was measured by maternal verbal reports. In addition, the pharmacy assessed the unused returned suspension. The aim of this sub-study was to determine the reliability of maternal verbal reports in measuring adherence to antiretroviral prophylaxis in infants in the first 6 weeks of life and evaluating the unused returned nevirapine as an alternative method of measuring adherence.

METHODS

Maternal verbal reports and pharmacy returns indicative of "missed < 2 doses" were evaluated against a plasma nevirapine concentration of >100 ng/ml in a subgroup of infants at 2, 5 and 6 weeks of age. Plasma nevirapine concentration of >100 ng/ml was used as a marker of adherence (10 times the in vitro IC50 against HIV).

RESULTS

Adherence was 87.7% (maternal verbal report) and 71.3% (unused returned medication), as compared to 85.6% by plasma nevirapine concentration. Evaluated against plasma nevirapine concentration <100 ng/ml, the sensitivity and specificity of maternal verbal reports to detect a missed dose in the last 3 days were 75% and 78% (p = 0.03) respectively. Overall, among infants who were classified as adherent based on missed doses by maternal verbal reports and unused returned medication, 88.4% and 87.4% of infants attained a nevirapine concentration above 100 ng/ml respectively.

CONCLUSION

Maternal verbal reports are a reliable measure of adherence to infant antiretroviral prophylaxis in the first 6 weeks of life and could be useful in assessing adherence to antiretroviral treatment in infants younger than 6 weeks. In the absence of resources or expertise to determine plasma drug concentration, we would recommend random assessments of unused returned medication.

Population pharmacokinetics of nevirapine in Thai HIV-infected patients

BACKGROUND

Nevirapine-based antiretroviral therapy is widely used as a first-line treatment for HIV-infected patients in resource-limited settings. Nevirapine plasma concentration has been shown to be associated with virological response and treatment failure. Therefore, identifying sources of the variability of nevirapine pharmacokinetics is important for dose optimization. The purpose of the current study was to determine the population mean pharmacokinetic parameters and identify factors that influence pharmacokinetic parameters of nevirapine in Thai HIV-infected patients.

METHODS

The model was developed by a non-linear mixed-effects modelling approach using NONMEM. Model validation was performed using bootstrap analysis and external validation. Additionally, nevirapine plasma concentrations of 200 mg twice daily (NVPBID) and 400 mg once daily (NVPOD) were simulated using the final model to investigate the impact of the covariates and different dosage regimens on nevirapine steady state concentrations.

RESULTS

The apparent clearance (CL/F) of nevirapine estimated from this population was 2.51 l/h which is lower than the values previously reported in other populations. The concomitant use of rifampicin increased CL/F by 20%. Simulated nevirapine plasma concentrations from NVPBID were superior to the NVPOD regimen.

CONCLUSIONS

This population-based pharmacokinetic model can be used for optimizing nevirapine dosage regimens for individual patients to improve efficacy and safety of nevirapine therapy in this population.

Population pharmacokinetic and pharmacogenetic analysis of nevirapine in hypersensitive and tolerant HIV-infected patients from Malawi

We modeled nevirapine (NVP) pharmacokinetics in HIV-infected Malawian patients to assess the relationship between drug exposure and patient characteristics, genetic polymorphisms, and development of hypersensitivity reaction (HSR). One thousand one hundred seventeen patients were prospectively recruited and followed for 26 weeks with multiple or single serum samples obtained in a subset of patients for NVP quantification. Single nucleotide polymorphisms (SNPs) within CYP2B6 and CYP3A4 genes were typed. Nonlinear mixed effects modeling was utilized to assess the influence of patient characteristics and host genetics on NVP apparent oral clearance (CL/F) and to explore the relationship between NVP CL/F and HSR. Published haplotype distributions were used to simulate NVP concentrations in Caucasians versus Africans. One hundred eighty patients (101 female) were included in the model; 25 experienced HSR. No associations between patient demographics or HSR and NVP CL/F were evident. A significant relationship between CYP2B6 c.983T>C and CYP2B6 c.516G>T and NVP CL/F was observed (P < 0.01). NVP CL/F was reduced by 23% and 36% in patients with CYP2B6 983TT/516TT and 983TC/516GG or GT, respectively, compared to the reference genotype. Simulated exposures suggested similar proportions (13 to 17%) of patients with subtherapeutic NVP among Caucasians and an African population. Influence of CYP2B6 polymorphisms on NVP CL/F in this population is in agreement with other reports. Our data indicate a lack of association between NVP exposure and HSR. Based on these data, dose optimization based solely on ethnicity (without individual gene testing) is unlikely to impact on risk of treatment failure or toxicity even in an African population with high carriage of poor metabolizer mutations.

Differences in nevirapine biotransformation as a factor for its sex-dependent dimorphic profile of adverse drug reactions

OBJECTIVES

Nevirapine is widely used for the treatment of HIV-1 infection; however, its chronic use has been associated with severe liver and skin toxicity. Women are at increased risk for these toxic events, but the reasons for the sex-related differences are unclear. Disparities in the biotransformation of nevirapine and the generation of toxic metabolites between men and women might be the underlying cause. The present work aimed to explore sex differences in nevirapine biotransformation as a potential factor in nevirapine-induced toxicity.

METHODS

All included subjects were adults who had been receiving 400 mg of nevirapine once daily for at least 1 month. Blood samples were collected and the levels of nevirapine and its phase I metabolites were quantified by HPLC. Anthropometric and clinical data, and nevirapine metabolite profiles, were assessed for sex-related differences.

RESULTS

A total of 52 patients were included (63% were men). Body weight was lower in women (P = 0.028) and female sex was associated with higher alkaline phosphatase (P = 0.036) and lactate dehydrogenase (P = 0.037) levels. The plasma concentrations of nevirapine (P = 0.030) and the metabolite 3-hydroxy-nevirapine (P = 0.035), as well as the proportions of the metabolites 12-hydroxy-nevirapine (P = 0.037) and 3-hydroxy-nevirapine (P = 0.001), were higher in women, when adjusted for body weight.

CONCLUSIONS

There was a sex-dependent variation in nevirapine biotransformation, particularly in the generation of the 12-hydroxy-nevirapine and 3-hydroxy-nevirapine metabolites. These data are consistent with the sex-dependent formation of toxic reactive metabolites, which may contribute to the sex-dependent dimorphic profile of nevirapine toxicity.

Physiologically based pharmacokinetic models for the optimization of antiretroviral therapy: recent progress and future perspective

Anti-HIV therapy is characterized by the chronic administration of antiretrovirals (ARVs), and consequently, several problems can arise during the management of HIV-positive patients. ARV disposition can be simulated by combining system data describing a population of patients and in vitro drug data through physiologically based pharmacokinetic (PBPK) models, which mathematically describe absorption, distribution, metabolism and elimination. PBPK modeling can find application in the investigation of clinically relevant scenarios, while providing the opportunity for a better understanding of the mechanisms regulating drug distribution. In this review, we have analyzed the most recent applications of PBPK models for ARVs and highlighted some of the most interesting areas of use, such as drug–drug interaction, pharmacogenetics, factors regulating absorption and tissue penetration, as well as therapy optimization in special populations. The application of the PBPK modeling approach might not be limited to the investigation of hypothetical clinical issues, but could be used to inform future prospective clinical trials.

Multiple genetic variants predict steady-state nevirapine clearance in HIV-infected Cambodians

OBJECTIVE

In a previous analysis involving protocol ANRS 12154, interindividual variability in steady-state nevirapine clearance among HIV-infected Cambodians was partially explained by CYP2B6 516G→T (CYP2B6*6). Here, we examine whether additional genetic variants predict nevirapine clearance in this cohort.

METHODS

Analyses included Phnom Penh ESTHER (Ensemble pour une Solidarité Thérapeutique Hospitalière en Réseau) cohort participants who had consented for genetic testing. All participants were receiving nevirapine plus two nucleoside analogs. The mean individual nevirapine clearance estimates were derived from a population model developed on nevirapine concentrations at 18 and 36 months of therapy. Polymorphisms were assayed in ABCB1, CYP2A6, CYP2B6, CYP2C19, CYP3A4, CYP3A5, and NR1I2.

RESULTS

Of 198 assayed loci, 130 were polymorphic. Among 129 individuals with evaluable genetic data, nevirapine clearance ranged from 1.06 to 5.00 l/h in 128 individuals and was 7.81 l/h in one individual. In bivariate linear regression, CYP2B6 516G→T (CYP2B6*6) was associated with lower nevirapine clearances (P=3.5×10). In a multivariate linear regression model conditioned on CYP2B6 516G→T, independent associations were identified with CYP2B6 rs7251950, CYP2B6 rs2279343, and CYP3A4 rs2687116. The CYP3A4 association disappeared after censoring the outlier clearance value. A model that included CYP2B6 516G→T (P=1.0×10), rs7251950 (P=4.8×10), and rs2279343 (P=7.1×10) explained 11% of interindividual variability in nevirapine clearance.

CONCLUSION

Among HIV-infected Cambodians, several CYP2B6 polymorphisms were associated independently with steady-state nevirapine clearance. The prediction of nevirapine clearance was improved by considering several polymorphisms in combination.

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.

Comparison of nevirapine plasma concentrations between lead-in and steady-state periods in Chinese HIV-infected patients

Objectives

To investigate the potential of nevirapine 200 mg once-daily regimen and evaluate the influence of patient characteristics on nevirapine concentrations.

Methods

This was a prospective, multicentre cohort study with 532 HIV-infected patients receiving nevirapine as a part of their initial antiretroviral therapy. Plasma samples were collected at trough or peak time at the end of week 2 (lead-in period) and week 4, 12, 24, 36, and 48 (steady-state period), and nevirapine concentrations were determined using a validated HPLC method. Potential influencing factors associated with nevirapine concentrations were evaluated using univariate and multivariate logistic regression.

Results

A total of 2348 nevirapine plasma concentrations were collected, including 1510 trough and 838 peak values. The median nevirapine trough and peak concentration during the lead-in period were 4.26 µg/mL (IQR 3.05–5.61) and 5.07 µg/mL (IQR 3.92–6.44) respectively, which both exceeded the recommended thresholds of nevirapine plasma concentrations. Baseline hepatic function had a moderate effect on median nevirapine trough concentrations at week 2 (4.25 µg/mL v.s. 4.86 µg/mL, for ALT <1.5×ULN and ≥1.5×ULN, respectively, P = 0.045). No significant difference was observed in median nevirapine trough concentration between lead-in and steady-state periods in patients with baseline ALT and AST level ≥1.5×ULN (P = 0.171, P = 0.769), which was different from the patients with ALT/AST level <1.5ULN. The median trough concentrations were significantly higher in HIV/HCV co-infected patients than those without HCV at week 48 (8.16 µg/mL v.s. 6.15 µg/mL, P = 0.004).

Conclusions

The 200 mg once-daily regimen of nevirapine might be comparable to twice-daily in plasma pharmacokinetics in Chinese population. Hepatic function prior to nevirapine treatment and HIV/HCV coinfection were significantly associated with nevirapine concentrations.

Registration

Clinicaltrial.gov ID: NCT00872417

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.

Influence of CYP2B6 and ABCB1 SNPs on nevirapine plasma concentrations in Burundese HIV-positive patients using dried sample spot devices

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

• Nevirapine pharmacokinetics are affected by several factors including CYP2B6 single nucleotide polymorphisms (SNPs). These genetic profiles are more common in African patients and they affect the drug clearance being associated with higher trough concentrations. Pharmacokinetic/pharmacogenetic (PK/PG) studies are difficult to perform in remote areas where refrigeration is not available, although dried plasma and dried blood methods have been validated.

WHAT THIS STUDY ADDS

• Dried plasma spots are useful tools for studying nevirapine PK with a good association to plasma concentrations and they can be used in rural areas since a cold chain is not necessary. Dried blood spots can be used to store and analyze patients' DNA for PG polymorphisms. Nevirapine trough concentrations in Burundese patients, not studied so far, are above the target concentration (3000 ng ml(-1) ) in 84% of patients. CYP2B6 (both at position 516 and 983) but not ABCB1 (3435 and 1236) SNPs as well as age correlate with higher nevirapine exposure.

AIMS

The pharmacokinetics (PK) and pharmacogenetics (PG) of nevirapine have been studied in rich and limited-resource countries. CYP2B6 single nucleotide polymorphisms (SNPs) have been associated with decreased drug clearance. We evaluated the PG determinants of nevirapine trough concentrations in a rural cohort in Burundi using easy to store and transport dried sample spot devices.

METHODS

A cross-sectional analysis in HIV-positive nevirapine-treated patients in Kiremba, north of Burundi, was performed in 2009. After blood withdrawal whole blood was stored on dried blood spots and plasma (after centrifugation) was placed on dried plasma spot devices and stored at room temperature. Nevirapine plasma and dried sample spot concentrations were compared to test the clinical usefulness of this method. SNPs in CYP2B6 and ABCB1 (using a real time PCR technique) were analyzed and associated with nevirapine plasma trough concentrations.

RESULTS

Nevirapine concentrations measured on dried plasma spot devices were highly related to plasma concentrations in 60 patients, although a negative bias was observed (-18%). Nevirapine trough concentrations were above the target concentration (3000 ng ml(-1) ) in 84% of patients and they were associated with CYP2B6 SNPs (both at position 516 and 983). No effect of ABCB1 SNPs was noted.

CONCLUSIONS

Dried plasma spot devices are accurate tools for measuring nevirapine concentrations in rural settings where refrigeration is not available, despite a moderate underestimation bias. They allowed the evaluation of nevirapine concentrations in a cohort of HIV-infected people in rural Burundi, confirming very good exposure and correlation with PG polymorphisms in the CYP2B6 encoding gene.

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.

Worldwide variation in human drug-metabolism enzyme genes CYP2B6 and UGT2B7: implications for HIV/AIDS treatment

AIM

Hepatic enzymes, CYP2B6 and UGT2B7 play a major role in the metabolism of the widely used antiretroviral drugs efavirenz, nevirapine and zidovudine. In the present study, we provide a view of UGT2B7 haplotype structure, and quantify the genetic diversity and differentiation at both CYP2B6 and UGT2B7 genes on a worldwide scale.

MATERIALS & METHODS

We genotyped one intronic and three promoter SNPs, and together with three nonsynonymous SNPs, inferred UGT2B7 alleles in north American (n = 326), west African (n = 133) and Papua New Guinean (n = 142) populations. We also included genotype data for five CYP2B6 and six UGT2B7 SNPs from an additional 12 worldwide populations (n = 629) analyzed in the 1000 Genomes Project.

RESULTS

We observed significant differences in certain SNP and allele frequencies of CYP2B6 and UGT2B7 among worldwide populations. Diversity values were higher for UGT2B7 than for CYP2B6, although there was more diversity between populations for CYP2B6. For both genes, most of the genetic variation was observed among individuals within populations, with the Papua New Guinean population showing the highest pairwise differentiation values for CYP2B6, and the Asian and European populations showing higher pairwise differentiation values for UGT2B7.

CONCLUSION

These new genetic distinctions provide additional insights for investigating differences in antiretroviral pharmacokinetics and therapy outcomes among ethnically and geographically diverse populations.