Dose Optimization of Efavirenz Based on Individual CYP2B6 Polymorphisms in Chinese Patients Positive for HIV

Effect of albumin and CYP2B6 polymorphisms on exposure of efavirenz: A population pharmacokinetic analysis in Chinese HIV-infected adults

BACKGROUND

Efavirenz is a vital component used to treat HIV-1 infection. Nevertheless, it shows large between-subject variability, which affects both its therapeutic response and adverse effects.

OBJECTIVE

To investigate the impact of gene polymorphisms and non-genetic factors on the variability of efavirenz pharmacokinetics and to propose the optimal dose regimens.

METHODS

A total of 769 plasma samples from 376 HIV-infected Han Chinese outpatients were collected to develop a population pharmacokinetic model using NONMEM software. The impact of patient demographics, laboratory tests, concomitant medication, and genetic polymorphisms of CYP2B6 and ABCB1 on efavirenz pharmacokinetics were explored. According to the final model, the model-informed dose optimization was conducted.

RESULTS

The pharmacokinetics of efavirenz was characterized by a one-compartment model with first-order absorption and elimination. The typical values of the estimated apparent oral clearance, volume of distribution, and absorption rate constant in the final model were 9.44 L/h, 200 L, and 0.727 h ^- 1, respectively. Efavirenz clearance was significantly influenced by CYP2B6 variants, including rs2099361, rs3745274, and rs2279343, along with albumin and weight. The volume of distribution was affected by albumin and weight. Based on the CYP2B6 polymorphisms of patients, the recommended daily doses of efavirenz were 100 mg for CYP2B6 slow metabolizers, 400 or 600 mg for intermediate metabolizers, and 800 or 1000 mg for extensive metabolizers.

CONCLUSIONS

Polymorphisms of CYP2B6, along with albumin and weight, resulted as the predictors of efavirenz pharmacokinetic variability, which could be used in prescribing optimal efavirenz doses.

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

AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Meta-analysis of the effect of CYP2B6, CYP2A6, UGT2B7 and CAR polymorphisms on efavirenz plasma concentrations

BACKGROUND

Efavirenz primary metabolism is catalysed by CYP2B6 with minor involvement of CYP2A6. Subsequently, phase I metabolites are conjugated by UGT2B7, and constitutive androstane receptor (CAR) has been shown to transcriptionally regulate many relevant enzymes and transporters. Several polymorphisms occurring in the genes coding for these proteins have been shown to impact efavirenz pharmacokinetics in some but not all studies.

OBJECTIVES

A meta-analysis was performed to assess the overall effect of CYP2B6 rs3745274, CYP2A6 (rs28399454, rs8192726 and rs28399433), UGT2B7 (rs28365062 and rs7439366) and NR1I3 (rs2307424 and rs3003596) polymorphisms on mid-dose efavirenz plasma concentrations.

METHODS

Following a literature review, pharmacokinetic parameters were compiled and a meta-analysis for these variants was performed using Review Manager and OpenMetaAnalyst. A total of 28 studies were included.

RESULTS

Unsurprisingly, the analysis confirmed that individuals homozygous for the T allele for CYP2B6 rs3745274 had significantly higher efavirenz concentrations than those homozygous for the G allele [weighted standard mean difference (WSMD) = 2.98; 95% CI 2.19-3.76; P < 0.00001]. A subgroup analysis confirmed ethnic differences in frequency but with a similar effect size in each ethnic group (P = 0.96). Associations with CYP2A6 and UGT2B7 variants were not statistically significant, but T homozygosity for CAR rs2307424 was associated with significantly lower efavirenz concentrations than in C homozygotes (WSMD = -0.32; 95% CI -0.59 to -0.06; P = 0.02).

CONCLUSIONS

This meta-analysis provides the overall effect size for the impact of CYP2B6 rs3745274 and NR1I3 rs2307424 on efavirenz pharmacokinetics. The analysis also indicates that some previous associations were not significant when interrogated across studies.

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

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

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.

Dosage Optimization of Efavirenz Based on a Population Pharmacokinetic-Pharmacogenetic Model of HIV-infected Patients in Thailand

PURPOSE

Efavirenz exhibits high interindividual variability in plasma concentrations, leading to unpredictable efficacy and toxicity. Polymorphism of CYP2B6 516G > T has been found to predominantly contribute to efavirenz variability. However, dosage recommendations incorporating CYP2B6 516G > T polymorphism have not been investigated in the Thai population. This study aimed to develop a population model of the pharmacokinetic properties of efavirenz, and to investigate the impact of patients' characteristics and CYP2B6 516G > T polymorphism on the pharmacokinetic properties of efavirenz. Model-based simulations were performed to provide genotype-based dosage optimization in a Thai population.

METHODS

Plasma efavirenz concentrations measured at 12 h post-dose in 360 Thai HIV-infected patients with and without tuberculosis were analyzed by the nonlinear mixed-effects modeling approach. A 1-compartment model with first-order absorption and elimination was used for describing the pharmacokinetic properties of efavirenz.

FINDINGS

The allele frequency of CYP2B6 516G > T was 34.17%. The efavirenz oral clearance were 11.9, 8.0, and 2.8 L/h in patients weighing 57 kg and having the CYP2B6 516 GG, 516 GT, and 516 TT genotypes, respectively. The use of rifampicin increased efavirenz oral clearance by 28%. The results from the simulations suggest that efavirenz dosages of 400, 300, and 100 mg once daily in Thai HIV mono-infected patients, and 800, 600, and 200 mg once daily in HIV/tuberculosis co-infected patients carrying CYP2B6 516 GG, 516 GT, and 516 TT, respectively.

IMPLICATION

The results from this study provide a rationale for efavirenz dose adjustment based on CYP2B6 516G > T polymorphism in Thai HIV-infected patients, which could help to improve treatment outcomes in this population. ClinicalTrials.gov identifier: NCT01138267.

Pharmacokinetics, Pharmacodynamics, and Pharmacogenetics of Efavirenz 400 mg Once Daily During Pregnancy and Post-Partum

Background

A clinical trial showed that efavirenz 400 mg once daily (EFV400) is as effective as the standard adult dose. World Health Organization recommends EFV400 as an alternative first-line agent, but data are lacking in the third trimester of pregnancy (TT). We investigated the pharmacokinetics, efficacy, and CYP2B6 pharmacogenetics in HIV-infected women (WLWH) on EFV400 during TT and post-partum (PP).

Methods

An open-label 2-center study (United Kingdom, Uganda) was conducted in WLWH receiving antiretroviral regimens containing efavirenz 600 mg, who had their efavirenz dose reduced to EFV400. Weekly therapeutic drug monitoring (TDM), steady-state pharmacokinetic profiles (TT and PP), safety, virological efficacy, and CYP2B6 polymorphisms at positions 516 (C > T) and 938 (T > C) were evaluated.

Results

Twenty-five WLWH of African origin were enrolled. All had viral loads <50 copies/mL at baseline, which were maintained throughout the study. No infant was HIV infected. No WLWH were withdrawn due to low EFV400 TDM results. Geometric mean ratios (TT/PP; 90% confidence interval) for EFV400 maximum observed plasma concentration, area under the curve, and plasma concentration measured 24 hours after the observed dose were 0.97 (.85-1.10), 0.87 (.76-.99), and 0.77 (.65-.91), respectively. Five of 25 WLWH were slow metabolizers.

Conclusions

Although EFV400 pharmacokinetic parameters were slightly lower for TT compared with PP values, efavirenz concentrations exceeded cutoff levels established by the study and those measured in antiretroviral-naive patients receiving EFV400 in ENCORE1. All subjects maintained a viral load <50 copies/mL, suggesting that EFV400 can be used in pregnant WLWH.

Meta-analysis of the associations of CYP2B6-516G>T polymorphisms with efavirenz-induced central nervous system side effects and virological outcome in HIV-infected adults

Clinical data on the relationships of cytochrome P450 (CYP2) B6 516G>T polymorphisms with efavirenz-induced central nervous system (CNS) side effects and virological response in HIV-infected adults are controversial. We sought to analyze the associations by meta-analysis. To identify eligible studies, we systematically searched PubMed, Embase, ScienceDirect, and Web of Science. The strength of the associations was measured by odds ratio (OR) and effect size (ES) with 95% confidence interval (CI). Seventeen studies comprising a total of 3598 HIV-infected adults were included. The results showed that the CYP2B6-516 GG genotype was significantly associated with a decreased risk of efavirenz-induced CNS side effects compared with the GT and TT genotypes (GG + GT vs. TT: OR = 0.60, 95% CI = 0.41-0.87, P = 0.006; GG vs. GT + TT: OR = 0.68, 95% CI = 0.51-0.91, P = 0.008; GG vs. GT: OR = 0.70, 95% CI = 0.51-0.94, P = 0.018), and there was no significant association between the genetic variants GT and TT (GT vs. TT: OR = 0.82, 95% CI = 0.54-1.26, P = 0.372). However, there was no significant association between CYP2B6-516 GG and GT + TT genotypes in virological response (GT + TT vs. GG: ES = 1.06, 95% CI = 0.95-1.18, P = 0.321; OR = 1.01, 95% CI = 0.65-1.58, P = 0.963). Taken together, our results demonstrated that compared with the normal efavirenz clearance genotype CYP2B6-516 GG, the slow and very slow efavirenz clearance genotypes GT and TT were significantly associated with an increased risk of efavirenz-induced CNS side effects but not an increased virological response. To promote the tolerance of efavirenz, it is better to adjust the dosage of efavirenz according to the polymorphisms of CYP2B6-516 in HIV-infected adults.

Pharmacogenetics of Antiretroviral Drug Response and Pharmacokinetic Variations in Indigenous South African Populations

Interindividual and interethnic differences in response to antiretroviral drugs (ARVs) are influenced by genetic variation. The few genomic studies conducted among African-Americans and African ethnic groups do not reflect the extensive genetic diversity within African populations. ARVs are widely used in Africa. Therefore, genomic characterization of African populations is required before genotype-guided dosing becomes possible. The aim of this study was to determine and report on the frequency of genetic variants in genes implicated in metabolism and transport of ARVs in South African populations. The study comprised 48 self-reported South African Colored (SAC) and 296 self-reported Black African (BA) individuals. Allele and genotype frequency distributions for 93 variants contributing to metabolism and transport of ARVs were compared between groups, and other global populations. Fifty-three variants had significant differences in allele and genotype frequencies when comparing SAC and BA groups. Thirteen of these have strong clinical annotations, affecting efavirenz and tenofovir pharmacokinetics. This study provides a summary of the genetic variation within genes implicated in metabolism and transport of ARVs in indigenous South African populations. The observed differences between indigenous population groups, and between these groups and global populations, demonstrate that data generated from specific African populations cannot be used to infer genetic diversity within other populations on the continent. These results highlight the need for comprehensive characterization of genetic variation within indigenous African populations, and the clinical utility of these variants in ARV dosing for global precision medicine. Population pharmacogenetics is a nascent field of global health and warrants further research and education.

Long-term efavirenz pharmacokinetics is comparable between Tanzanian HIV and HIV/Tuberculosis patients with the same CYP2B6*6 genotype

The impact of anti-tuberculosis co-treatment on efavirenz (EFV) exposure is still uncertain as contradictory reports exist, and the relevance of CYP2B6*6 genetic polymorphism on efavirenz clearance while on-and-off anti-tuberculosis co-treatment is not well investigated. We investigated the determinants of long-term efavirenz pharmacokinetics by enrolling HIV (n = 20) and HIV/Tuberculosis (n = 36) subjects undergoing efavirenz and efavirenz/rifampicin co-treatment respectively. Pharmacokinetic samplings were done 16 weeks after initiation of efavirenz-based anti-retroviral therapy and eight weeks after completion of rifampicin-based anti-tuberculosis treatment. Population pharmacokinetic modeling was used to characterize variabilities and covariates of efavirenz pharmacokinetic parameters. CYP2B6*6 genetic polymorphism but not rifampicin co-treatment was the statistically significant covariate. The estimated typical efavirenz clearance in the HIV only subjects with the CYP2B6*1/*1 genotype was 23.6 L/h/70 kg, while it was 38% and 69% lower in subjects with the CYP2B6*1/*6 and *6/*6 genotypes, respectively. Among subjects with the same CYP2B6 genotypes, efavirenz clearances were comparable between HIV and HIV/Tuberculosis subjects. Typical efavirenz clearances before and after completion of anti-tuberculosis therapy were comparable. In conclusion, after 16 weeks of treatment, efavirenz clearance is comparable between HIV and HIV/Tuberculosis patients with the same CYP2B6 genotype. CYP2B6 genotyping but not anti-tuberculosis co-treatment should guide efavirenz dosing to optimize treatment outcomes.

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.

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Population Pharmacokinetic Model Linking Plasma and Peripheral Blood Mononuclear Cell Concentrations of Efavirenz and Its Metabolite, 8-Hydroxy-Efavirenz, in HIV Patients

The objectives of this study were to characterize the population pharmacokinetics (PK) of efavirenz (EFV) and 8-hydroxy-efavirenz (8OHEFV) in plasma and peripheral blood mononuclear cells (PBMCs) and to explore covariates affecting the PK parameters. Fifty-one patients had steady-state 0-to-24-h concentrations of EFV and 8OHEFV in plasma with corresponding concentrations in PBMCs, while 261 patients had one or two sparse concentrations at 16 ± 1 h postdose at weeks 4 and/or 16. The pharmacogenetic markers CYP2B6*6, CYP3A5*3, CYP3A5*6, UGT2B7*2, ABCB1 (3435C→T, 3842A→G), OATP1B1*1B, and OATP1B1*5, the presence of a rifampin-based antituberculosis (anti-TB) regimen, baseline body weight and organ function values, and demographic factors were explored as covariates. EFV concentration data were well described by a two-compartment model with first-order absorption (K_a ) and absorption lag time (A_lag) (K_a = 0.2 h^-1; A_lag = 0.83 h; central compartment clearance [CL_c/F] for CYP2B6*1/*1 = 18 liters/h, for CYP2B6*1/*6 = 14 liters/h, and for CYP2B6*6/*6 = 8.6 liters/h) and PBMCs as a peripheral compartment. EFV transfer from plasma to PBMCs was first order (CL_p/F = 32 liters/h), followed by capacity-limited return (V_max = 4,400 ng/ml/h; K_m = 710 ng/ml). Similarly, 8OHEFV displayed a first-order elimination and distribution to PBMCs, with a capacity-limited return to plasma. No covariate relationships resulted in a significant explanation of interindividual variability (IIV) on the estimated PK parameters of EFV and 8OHEFV, except for CYP2B6*6 genotypes, which were consistent with prior evidence. Both EFV and 8OHEFV accumulated to higher concentrations in PBMCs than in plasma and were well described by first-order input and Michaelis-Menten kinetics removal from PBMCs. CYP2B6*6 genotype polymorphisms were associated with decreased EFV and 8OHEFV clearance.

The CYP2B6 G516T polymorphism influences CD4+ T-cell counts in HIV-positive patients receiving antiretroviral therapy in an ethnically diverse region of the Amazon

OBJECTIVES

Cytochrome P450 (CYP) enzyme polymorphisms seem to significantly influence the variability of the responses to certain antiretroviral drugs and their toxicity levels. The objective of this study was to evaluate the influence of the CYP2B6 G516T polymorphism on hepatic, renal, immunological, and viral marker changes in HIV-1-positive patients receiving treatment in an ethnically diverse region of the Amazon.

METHODS

CYP2B6 G516T genotyping was performed by real-time PCR (RT-PCR) in samples from 185 patients. Urea, creatinine, aspartate aminotransferase (AST), alanine aminotransferase (ALT), CD4⁺/CD8⁺ T-cell counts, and HIV-1 plasma viral load were measured.

RESULTS

The polymorphic CYP2B6 G516T allele frequency was 0.36, which is different from the frequencies in other ethnic groups. The polymorphic genotype was associated with changes in the urea and ALT levels, although the median values were within the normal range. The TT genotype was also associated with significantly lower CD4⁺ T-cell counts in patients using efavirenz.

CONCLUSIONS

The CYP2B6 G516T polymorphism seems to affect the response to efavirenz treatment by reducing CD4⁺ T-cell counts in patients with a high degree of miscegenation who use this antiretroviral agent.

Role of Cytochrome P450 2B6 Pharmacogenomics in Determining Efavirenz-Mediated Central Nervous System Toxicity, Treatment Outcomes, and Dosage Adjustments in Patients with Human Immunodeficiency Virus Infection

For treatment-naive patients with human immunodeficiency virus infection, efavirenz (EFV), together with tenofovir and emtricitabine, was once widely prescribed given its efficacy and ease of administration in a combination pill. However, the high rate of central nervous system (CNS) toxicities from EFV prompted the U.S. Department of Health and Human Services to move the EFV-based regimen from the recommended to the alternative category. For patients who do meet the criteria for newer recommended antiretroviral treatments, EFV is a viable option and often the mainstay of treatment outside the United States because newer antiretroviral treatments are more expensive. CNS toxicity occurring with the recommended standard dose of EFV remains a challenge and may in part be attributable to polymorphisms in cytochrome P450 (CYP) 2B6, the enzyme involved in the major metabolic pathway for converting EFV to inactive metabolites. Functionally deficient alleles of CYP2B6 such as CYP2B6*6, *18, and *22 may be responsible for significantly higher therapeutic concentrations of EFV at a standard dose of 600 mg/day. We conducted a thorough review of the reported studies to elucidate the relationship between polymorphisms in CYP2B6 with adverse events and treatment response, including virologic suppression, immunologic response, resistance, and discontinuation of treatment. Compelling evidence exists to support the case for CYP2B6 genotype-guided EFV therapy while acknowledging the need for prospective controlled clinical trials to evaluate its clinical utility.