Exploration of CYP450 and drug transporter genotypes and correlations with nevirapine exposure in Malawians

Pharmacogenetics of Breast Cancer Treatments: A Sub-Saharan Africa Perspective

Breast cancer is the most frequent cause of cancer death in low- and middle-income countries, in particular among sub-Saharan African women, where response to available anticancer treatment therapy is often limited by the recurrent breast tumours and metastasis, ultimately resulting in decreased overall survival rate. This can also be attributed to African genomes that contain more variation than those from other parts of the world. The purpose of this review is to summarize published evidence on pharmacogenetic and pharmacokinetic aspects related to specific available treatments and the known genetic variabilities associated with metabolism and/or transport of breast cancer drugs, and treatment outcomes when possible. The emphasis is on the African genetic variation and focuses on the genes with the highest strength of evidence, with a close look on CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP3A4/5, CYP19A1, UGT1A4, UGT2B7, UGT2B15, SLC22A16, SLC38A7, FcγR, DPYD, ABCB1, and SULT1A1, which are the genes known to play major roles in the metabolism and/or elimination of the respective anti-breast cancer drugs given to the patients. The genetic variability of their metabolism could be associated with different metabolic phenotypes that may cause reduced patients’ adherence because of toxicity or sub-therapeutic doses. Finally, this knowledge enhances possible personalized treatment approaches, with the possibility of improving survival outcomes in patients with breast cancer.

Pharmacogenetic predictors of nevirapine pharmacokinetics in Ghanaian children living with HIV with or without TB coinfection

Nevirapine (NVP) is a non-nucleoside reverse transcriptase inhibitor that is used in the treatment of human immunodeficiency virus (HIV) infection in children younger than 3 years old. Identifying genetic predictors of NVP pharmacokinetics (PK) in young children is important because inter-individual variability in NVP concentrations contributes to variable treatment response and the information may be used to individualize dosing decisions. We examined the relationship between genetic variations in relevant drug disposition genes and NVP PK parameters in Ghanaian children living with HIV eligible to initiate NVP-based antiretroviral therapy. Participants received NVP plus zidovudine and lamivudine or abacavir and lamivudine twice daily, and those with tuberculosis (TB) coinfection received concurrent anti-TB therapy with NVP. Pharmacokinetic sampling was performed after at least 4 weeks of antiretroviral therapy. Nevirapine minimum concentration (C_min), area under the concentration-time curve from time 0 to 12 h (AUC_0-12h), and apparent clearance (CL/F) were calculated using non-compartmental analysis using Phoenix v8.0 software. Genotyping for CYP2B6, CYP2A6, CYP3A5, ABCB1, NR1I2, and NR1I3 single nucleotide polymorphism (SNPs) was performed by TaqMan® allelic discrimination method. The median (range) NVP dose received was 10 (7-14) mg/kg. Of the 53 participants, the median (range) C_min was 3.3 (0.0-14.0) mg/L and AUC_0-12h was 56.0 (16.7-202.6) mg.hr/L. Using step-wise regression, CYP2B6 rs3745274 and NR1I2 rs6785049 SNPs were independent as well as joint predictors of NVP AUC_0-12h, C_min, and CL/F. We concluded that genotyping for CYP2B6 rs3745274, and the NR1I2 rs6785049 G > A SNP (which encodes the transcriptional factor, pregnane X receptor), could improve prediction of NVP PK for individualized therapy.

Pharmacogenetic considerations in the treatment of co-infections with HIV/AIDS, tuberculosis and malaria in Congolese populations of Central Africa

BACKGROUND

HIV-infection, tuberculosis and malaria are the big three communicable diseases that plague sub-Saharan Africa. If these diseases occur as co-morbidities they require polypharmacy, which may lead to severe drug-drug-gene interactions and variation in adverse drug reactions, but also in treatment outcomes. Polymorphisms in genes encoding drug-metabolizing enzymes are the major cause of these variations, but such polymorphisms may support the prediction of drug efficacy and toxicity. There is little information on allele frequencies of pharmacogenetic variants of enzymes involved in the metabolism of drugs used to treat HIV-infection, TB and malaria in the Republic of Congo (ROC). The aim of this study was therefore to investigate the occurrence and allele frequencies of 32 pharmacogenetic variants localized in absorption distribution, metabolism and excretion (ADME) and non-ADME genes and to compare the frequencies with population data of Africans and non-Africans derived from the 1000 Genomes Project.

RESULTS

We found significant differences in the allele frequencies of many of the variants when comparing the findings from ROC with those of non-African populations. On the other hand, only a few variants showed significant differences in their allele frequencies when comparing ROC with other African populations. In addition, considerable differences in the allele frequencies of the pharmacogenetic variants among the African populations were observed.

CONCLUSIONS

The findings contribute to the understanding of pharmacogenetic variants involved in the metabolism of drugs used to treat HIV-infection, TB and malaria in ROC and their diversity in different populations. Such knowledge helps to predict drug efficacy, toxicity and ADRs and to inform individual and population-based decisions.

Genetic Diversity in Drug Transporters: Impact in African Populations

Polymorphisms in drug transporters, like the adenosine triposphate-binding cassette (ABC) and solute carrier (SLC) superfamilies, may contribute to the observed diversity in drug response in African patients. This review aims to provide a comprehensive summary and analysis of the frequencies and distributions in African populations of ABC and SLC variants that affect drug pharmacokinetics (PK) and pharmacodynamics (PD). Of polymorphisms evaluated in African populations, SLCO1B1 rs4149056 and SLC22A6 rs1158626 were found at markedly higher frequencies than in non-African populations. SLCO1B1 rs4149056 was associated with reduction in rifampin exposure, which has implications for dosing this important anti-tuberculosis therapy. SLC22A6 rs1158626 was associated with increased affinity for antiretroviral drugs. Genetic diversity in SLC and ABC transporters in African populations has implications for conventional therapies, notably in tuberculosis and HIV. More PK and PD data in African populations are needed to assess potential for a different response to drugs compared with other global populations.

Differential Impact of Nevirapine on Artemether-Lumefantrine Pharmacokinetics in Individuals Stratified by CYP2B6 c.516G>T Genotypes

There is an increased recognition of the need to identify and quantify the impact of genetic polymorphisms on drug-drug interactions. This study investigated the pharmacogenetics of the pharmacokinetic drug-drug interaction between nevirapine and artemether-lumefantrine in HIV-positive and HIV-negative adult Nigerian subjects.

There is an increased recognition of the need to identify and quantify the impact of genetic polymorphisms on drug-drug interactions. This study investigated the pharmacogenetics of the pharmacokinetic drug-drug interaction between nevirapine and artemether-lumefantrine in HIV-positive and HIV-negative adult Nigerian subjects. Thirty each of HIV-infected patients on nevirapine-based antiretroviral therapy and HIV-negative volunteers without clinical malaria, but with predetermined CYP2B6 c.516GG and TT genotypes, were administered a complete treatment dose of 3 days of artemether-lumefantrine. Rich pharmacokinetic sampling prior to and following the last dose was conducted, and the plasma concentrations of artemether/dihydroartemisinin and lumefantrine/desbutyl-lumefantrine were quantified using tandem mass spectrometry. Pharmacokinetic parameters of artemether-lumefantrine and its metabolites in HIV-infected patients on nevirapine were compared to those in the absence of nevirapine in HIV-negative volunteers. Overall, nevirapine reduced exposure to artemether and desbutyl-lumefantrine by 39 and 34%, respectively. These reductions were significantly greater in GG versus TT subjects for artemether (ratio of geometric mean [90% confidence interval]: 0.42 [0.29 to 0.61] versus 0.81 [0.51 to 1.28]) and for desbutyl-lumefantrine (0.56 [0.43 to 0.74] versus 0.75 [0.56 to 1.00]). On the contrary, it increased exposure to dihydroartemisinin and lumefantrine by 47 and 30%, respectively. These increases were significantly higher in TT versus GG subjects for dihydroartemisinin (1.67 [1.20 to 2.34] versus 1.25 [0.88 to 1.78]) and for lumefantrine (1.51 [1.20 to 1.90] versus 1.08 [0.82 to 1.42]). This study underscores the importance of incorporating pharmacogenetics into all drug-drug interaction studies with potential for genetic polymorphisms to influence drug disposition.

Adverse Drug Reactions Associated with CYP 2B6 Polymorphisms in HIV/AIDS-Treated Patients in Yaoundé, Cameroon

PURPOSE

The metabolism of antiretroviral drugs is subject to individual variations of the CYP 2B6 gene. The objective of this study was to evaluate the prevalence of CYP 2B6 516 G>T and 983 T>C polymorphisms and investigate their association with the development of adverse drug reactions (ADRs) in people living with HIV/AIDS in Cameroon.

PATIENTS AND METHODS

A total number of 122 patients, attending the Yaoundé Central Hospital HIV Day Clinic, consented to take part in this study. Blood specimens were collected and DNA was extracted using the Chelex method. Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP) was performed for the detection of CYP 2B6 Single-Nucleotide Polymorphisms (SNPs). Genotype frequencies were compared between groups with or without ADRs. Logistic regression analysis was performed to assess association between genotype and adverse effects of antiretroviral therapy (ART).

RESULTS

Three types of metabolizers were identified: extensive, intermediate and slow. For the 516G>T polymorphism, prevalences of 8.2% GG, 65.6% GT and 26.2% TT were obtained. For the 983T>C polymorphism, 89.3% TT, 4.1% CT and 6.6% CC prevalences were obtained. Those homozygous for the wild-type allele (516GG) were less likely to develop ADR with a statistically significant difference (OR=0.885, P=0.029). For the CYP2B6 T983C SNP, homozygous mutants (CC) may present a higher risk (threefold) of developing adverse reactions (OR=2.677, P=0.164).

CONCLUSION

These findings demonstrate that ADRs among HIV/AIDS patients under ART may be associated with the genetic variability of the metabolizing enzyme CYP 2B6. Genotyping for this gene may guide the better administration of Efavirenz and Nevirapine to Cameroonian patients.

Estimation of Drug Pharmacokinetics from Breast Feeding: A Simple Method Based on Meta-analysis

Background:

In resource-limited settings, breastfeeding is the healthiest source of nutrition for newborns. For economic/cultural reasons, breastfeeding is the preferred option for the majority of mothers, including HIV-positive mothers.

Objective:

The objective of this review is to document parameters characterizing antiretroviral therapy (ARV) diffusion into breast milk associated with the estimated ARV amount ingested by breastfed infant and clinical/biological abnormalities.

Data Source and Eligibility Criteria:

Twenty seven (27) published articles on the aspects of Pharmacokinetic parameters on ARV diffusion into breast milk have shown a large variability without clear interpretation on drugs diffusion. Using PubMed and Embase, we conducted a search to identify all published studies at 2015 that characterized antiretroviral drug diffusion from mother to infant via breast milk. We identified 27 published studies that characterized antiretroviral drug passage from mother to infant (drug concentrations in mother’s milk and breastfed plasma). Information was sufficiently complete for inclusion in the present analysis for only six antiretroviral drugs.

Results:

Finally, only data for nevirapine and efavirenz were exploitable because some of the studies found null or non-detectable levels, which were not suitable for simulations. Median (IQR) nevirapine CL/F were 0.022 (0.013–0.038) for newborns, 0.121 (0.116–0.125) for children and 0.056 (0.045–0.070) for mothers, all in L/h/kg. Efavirenz CL/F were 0.025 (0.016–0.039) for newborns, 0.273 (0.261–0.285) for children and 0.160 (0.153–0.167) for mothers, also in L/h/kg.

Conclusion:

Pharmacokinetics parameters of efavirenz and nevirapine are important to be determined in breastfed newborns.

Prevalence of CYP2D6*4 1934G/A polymorphism in Western Indian HIV patients

Hepatic CYP2D6 enzyme metabolizes antiretroviral drugs (ARVs) including nevirapine. Polymorphism in CYP2D6 gene affects drug metabolism and displays distinctive phenotypes in the population. Hence, we investigated the prevalence of CYP2D6*4 1934G/A polymorphism in a total of 165 HIV patients that include 34 with and 131 without hepatotoxicity and 160 unrelated healthy controls by the PCR-RFLP method. The prevalence of CYP2D6*4 1934AA genotype was higher in total HIV patients as compared to healthy controls (1.81% vs 0.6%, OR = 2.86). Similarly, CYP2D6*4 1934AA genotype was much more prevalent in HIV patients without hepatotoxicity as compared to healthy controls (2.3% vs 0.6%, OR = 2.87). Likewise, CYP2D6*4 1934AA genotype was predominant in advanced HIV disease stage as compared to healthy controls (3.8% vs 0.6%, OR = 6.15). CYP2D6*4 1934GA genotype was distributed higher in HIV patients taking tobacco and nevirapine as compared to non-users (23.3% vs 19.3%, OR = 1.21, 21.0% vs 16.7%, OR = 1.2). Likewise, CYP2D6*4 1934GA genotype was overrepresented in patients with hepatotoxicity taking alcohol + nevirapine as compared to alcohol non-users + nevirapine users (20.00% vs 16.67%, OR = 1.25). Thus, there was no significant difference in genotype or allele frequencies of CYP2D6*4 1934G/A polymorphism between the patients with hepatotoxicity and those without or healthy controls.

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.

Genetic variations of the xenoreceptors NR1I2 and NR1I3 and their effect on drug disposition and response variability

NR1I2 (PXR) and NR1I3 (CAR) are nuclear receptors that are classified as xenoreceptors. Upon activation by various xenobiotics, including marketed drugs, they regulate the transcription level of major drug-metabolizing enzymes and transporters and facilitate the elimination of xenobiotics from the body. The modulation of the activity of these two xenoreceptors by various ligands is a major source of pharmacokinetic variability of environmental origin. NR1I2 and NR1I3 genetic polymorphisms can affect the pharmacokinetics and therapeutic response to many drugs, such as irinotecan, tacrolimus and atazanavir. This review provides an overview of NR1I2 and NR1I3 pharmacogenetic studies in various therapeutic fields (oncology, immunomodulation and infectiology) and discusses the implementation of NR1I2 and NR1I3 genetic polymorphism testing in the clinical routine.

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.

Pharmacokinetic, Pharmacogenetic, and Other Factors Influencing CNS Penetration of Antiretrovirals

Neurological complications associated with the human immunodeficiency virus (HIV) are a matter of great concern. While antiretroviral (ARV) drugs are the cornerstone of HIV treatment and typically produce neurological benefit, some ARV drugs have limited CNS penetration while others have been associated with neurotoxicity. CNS penetration is a function of several factors including sieving role of blood-brain and blood-CSF barriers and activity of innate drug transporters. Other factors are related to pharmacokinetics and pharmacogenetics of the specific ARV agent or mediated by drug interactions, local inflammation, and blood flow. In this review, we provide an overview of the various factors influencing CNS penetration of ARV drugs with an emphasis on those commonly used in sub-Saharan Africa. We also summarize some key associations between ARV drug penetration, CNS efficacy, and neurotoxicity.

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.

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.

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.

Pharmacogenetics of CYP2B6, CYP2A6 and UGT2B7 in HIV treatment in African populations: focus on efavirenz and nevirapine

The CYP450 and UGT enzymes are involved in phase I and phase II metabolism of the majority of clinically prescribed drugs, including the non-nucleoside reverse transcriptase inhibitors, efavirenz and nevirapine, used in the treatment of HIV/AIDS. Variations in the activity of these enzymes due to gene polymorphisms can affect an individual's drug response or may lead to adverse drug reactions. There is an inter-ethnic distribution in the frequency of these polymorphisms, with African populations exhibiting higher genetic diversity compared to other populations. African specific alleles with clinical relevance have also emerged. Given the high prevalence of HIV/AIDS in sub-Saharan Africa, understanding the frequency of pharmacogenetically relevant alleles in populations of African origin, and their impact on efavirenz and nevirapine metabolism, is becoming increasingly critical. This review aims to investigate ethnic variation of CYP2B6, CYP2A6 and UGT2B7, and to understand the pharmacogenetic relevance when comparing frequencies in African populations to other populations worldwide.

Different frequencies of drug resistance mutations among HIV-1 subtypes circulating in China: a comprehensive study

The rapid spreading of HIV drug resistance is threatening the overall success of free HAART in China. Much work has been done on drug-resistant mutations, however, most of which were based on subtype B. Due to different genetic background, subtypes difference would have an effect on the development of drug-resistant mutations, which has already been proved by more and more studies. In China, the main epidemic subtypes are CRF07_BC, CRF08_BC, Thai B and CRF01_AE. The depiction of drug resistance mutations in those subtypes will be helpful for the selection of regimens for Chinese. In this study, the distributions difference of amino acids at sites related to HIV drug resistance were compared among subtype B, CRF01_AE, CRF07_BC and CRF08_BC strains prevalent in China. The amino acid composition of sequences belonging to different subtypes, which were obtained from untreated and treated individuals separately, were also compared. The amino acids proportions of 19 sites in RT among subtype B, CRF01_AE and CRF08_BC have significant difference in drug resistance groups (chi-square test, p<0.05). Genetic barriers analysis revealed that sites 69, 138, 181, 215 and 238 were significantly different among subtypes (Kruskal Wallis test, p<0.05). All subtypes shared three highest prevalent drug resistance sites 103, 181 and 184 in common. Many drug resistant sites in protease show surprising high proportions in almost all subtypes in drug-naïve patients. This is the first comprehensive study in China on different development of drug resistance among different subtypes. The detailed data will lay a foundation for HIV treatment regimens design and improve HIV therapy in China.

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.

Potential effect of pharmacogenetics on maternal, fetal and infant antiretroviral drug exposure during pregnancy and breastfeeding

Mother-to-child-transmission rates of HIV in the absence of any intervention range between 20 and 45%. However, the provision of antiretroviral drugs (ARVs) during pregnancy, delivery and breastfeeding can reduce HIV transmission to less than 2%. Physiological changes during pregnancy can influence ARV disposition. Associations between SNPs in genes coding for metabolizing enzymes, and/or transporters, and ARVs disposition are well described; however, relatively little is known about the influence of these SNPs on ARV pharmacokinetics during pregnancy and lactation as well as their effect on distribution into the fetal compartment and breast milk excretion. Differences in maternal, fetal and infant ARV exposure due to SNPs may affect the efficacy and safety of ARVs used to prevent mother-to-child-transmission. The aim of this review is to provide an update on the effect of pregnancy-induced changes on the pharmacokinetics of ARVs and highlight the potential role of pharmacogenetics.

ABCB1 4036A>G and 1236C>T Polymorphisms Affect Plasma Efavirenz Levels in South African HIV/AIDS Patients

The ABCB1 gene encodes P-glycoprotein, an ATP-dependent drug efflux pump, which is responsible for drug transport across extra- and intra-cellular membranes. The variability in the expression of ABCB1 may contribute to variable plasma efavirenz concentration which results in variability in the levels of suppression of the human immunodeficiency syndrome virus (HIV). The aim of the study was to evaluate the role of polymorphisms in ABCB1 gene on plasma efavirenz levels and treatment response in the form of change in viral load and CD-4 cell count in HIV/AIDS patients receiving efavirenz-containing highly active antiretroviral treatment regimens. Two hundred and eighty-two HIV-infected patients were recruited from Themba Lethu Clinic in Johannesburg and plasma efavirenz drug concentration levels were measured using LC-MS/MS. SNaPshot was used to genotype five known ABCB1 single nucleotide polymorphisms (SNPs). Genotype-phenotype correlations were computed. The ABCB1 4036A/G and 4036G/G genotypes were significantly associated with low plasma efavirenz concentrations (P = 0.0236), while the ABCB1 1236C/T and 1236T/T genotypes were associated with high efavirenz concentrations (P = 0.0282). A haplotype ABCB1 T-G-T-A is reported that is associated with significantly increased plasma efavirenz levels. This is the first report on 61A>G, 2677G>T/A, and 4036A>G SNPs in the South African population. ABCB1 plays a role in determining the plasma concentrations of efavirenz and should be taken into account in future design of assays for genotype-based dosing of efavirenz-containing regimens.