Efavirenz Plasma Levels Research Articles

#4355 THE INFLUENCE OF ANTIRETROVIRAL DRUGS AND HIV RESISTANCE MUTATIONS ON THE SHEDDING OF HIV-1 INTO PERITONEAL DIALYSIS EFFLUENT

Abstract Background and Aims Antiretroviral therapy (ART) is effective HIV management even in HIV-positive patients with end-stage kidney failure (ESKF). However, drug resistance mutations are important determinants of therapeutic effects. The study aimed to determine the prevalence of HIV resistance mutations and ART drug penetration in the peritoneal compartment and their effect on the shedding of HIV-1 into continuous ambulatory peritoneal dialysis (CAPD) effluents. Method This prospective cross-sectional study of HIV-positive ESKF patients managed with ART and CAPD at Universitas Academic Hospital collected enrolled patients' background information and clinical and laboratory data. HIV-1 was detected using quantitative polymerase chain reaction (qPCR) and sequenced by the Sanger method, while ART levels were quantified using LC-MS/MS. Results There were 38 patients recruited with a median age of 41.8 (IQR, 36.15–48.0) years and were predominantly on abacavir (89.5%), lamivudine (100%) and efavirenz (76.3%) for a median duration of 8 (IQR, 6–11) years. Among participants with detectable HIV in CAPD effluents, the prevalence of ARV-drug resistance mutations was 71.4% (5/7) compared to 12.9% (4/31) among those with undetectable HIV-1 (p = 0.004) with NNRTI resistance mutations predominating. Participants with detectable HIV-1 had lower abacavir (0.00182 vs 5.68 ng/µl; p = 0.021), lamivudine (0.0152 vs 1.09 ng/µl; p = 0.001) and efavirenz (3,605 vs. 57,8 ng/µl; p = 0.004) plasma levels compared to those with undetectable HIV-1. Measured lamivudine (0.455 vs 0.342 ng/µl; p = 0.007) and efavirenz (46.5 vs 2.34 ng/µl; p<0.001) drug levels are significantly higher in plasma than CAPD effluents. Conclusion ART resistance mutations, lower drug levels and poor compartment penetration are suggested significant factors for HIV-1 shedding into CAPD effluents.

Plasma levels of efavirenz and frequency of the CYP2B6 516G>T polymorphism in people living with HIV-1 in Mexico.

Efavirenz (EFV) is a widely used antiretroviral, due to its safety, efficacy, and low cost. However, plasma concentrations have been related with an increased risk of virological failure and the appearance of serious adverse reactions. EFV is metabolized by Cytochrome P450, the main isoenzyme involved is CYP2B6 and the most relevant genetic polymorphisms found in several populations has been the CYP2B6 516G> T. The aim of this study was to identify the frequency of the CYP2B6 516G>T polymorphism and its effect on the plasma concentration of efavirenz (EFV) in a group of people living with HIV (PLWH) and undergoing EFV treatment in Morelos, Mexico. Ninety-six PLWH undergoing EFV treatment, at a daily dose of 600 mg orally in combination with other antiretrovirals (ARVs), were included in this study. The CYP2B6 516G>T polymorphism was detected using PCR-RFLP. The plasma concentrations of EFV were evaluated by high-resolution liquid chromatography coupled to a mass-mass detector, using a protein precipitation method. The median plasma EFV concentration was 4.6 μg/mL (IQR = 4.64) and 64.6% of the subjects had concentrations above the therapeutic range. The CYP2B6 516G>T genotype findings were as follows: 46.9% of the population presented the wild-type genotype (GG), while 45.8 % and 7.3 % showed the heterozygote (GT) and the polymorphic homozygote (TT) genotype, respectively. The homozygote G had the lowest plasma concentrations of EFV (median = 4.1 μg/mL and IQR = 1.7 μg/mL), followed by those with the GT genotype (median = 5.1 μg/mL and IQR = 3.0 μg/mL). Participants with the homozygous T genotype had the highest EFV concentrations (median = 9.7 μg/mL and IQR = 5.8 μg/mL). In conclusion, the CYP2B6 516G>T polymorphism was associated with plasma levels of EFV in PLWH undergoing ARV treatment. EFV plasma concentrations at 600mg doses were outside the therapeutic range in most subjects.

The Cyp2b6 Gene Polymorphism and Phenotypic Correlation of Efavirenz-Based Combination Therapy Among the Niger Delta Ethnic Population: Implications in Modern Pharmacogenomics.

PurposeDNA polymorphism describes the difference between individuals, groups, or ethnicities, races, etc., in terms of their DNA sequences or phenotypes as relates to drug metabolism. Using predictive genotyping of drug-metabolizing genes, we can develop individuals’ drug therapies that are less toxic and more effective. The main aim of the study was to evaluate genotype–phenotype-based correlation and incidence of genetic polymorphism of efavirenz blood levels among HIV/AIDS patients of the Niger Delta population.MethodsA study questionnaire was designed to obtained patients’ data, blood samples were obtained, plasma was separated from the serum using a centrifuge for 5 minutes at 4000 rpm for HPLC analysis, polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) analysis was conducted using Bsrl endonuclease enzyme to digest the PCR amplicons. Standard efavirenz was used at 0.5, 1, 2, 4, 16 mg/L to construct a calibration curve. Data were analyzed with SPSS software using chi-square test at p-value ≤0.5 and Microsoft excel 2013, while PCR and RFLP results were obtained after 1% Agarose gel electrophoresis, respectively.ResultsPhenotypic results showed that the participants had different efavirenz plasma concentrations. Six subjects (12%) had efavirenz plasma levels below 0.10 mg/L, considered ultra-rapid metabolizers (UMs), 22 (44%) 0.10 mg/L to 0.90 mg/L, classified as extensive metabolizers (EMs), 19 (38%) had 1.0 to 3.9 mg/L and were noted as intermediate metabolizers (IM), while 3 (6%) subjects showed efavirenz plasma levels from 4.0 mg/L to 6.0 mg/L, categorized as poor metabolizers (PM). RFLP results showed more than half of the population (56%) with a homozygous wild-type gene with CYP2B6*1*1 allele, 38% were CYP2B6*1*6 (heterozygous mutant) allele and 6% had homozygous mutant gene (CYP2B6*6*6 allele). Out of the 15 male subjects among the 50 patients that participated in the study, 8% were UM, 12% EM, 14% IM while no PM was observed, on the contrary, out of the 35 females participated in the study, 4% were observed as UM, 32% EM, 24% IM, while 6% were PM.ConclusionThere was no significant difference (p ≤ 0.05) between genotype and phenotype data for CYP2B6 polymorphism, among the HIV/AIDS patients that participated in this study. Genetic polymorphism of the CYP2B6 gene is prevalent among HIV/AIDs patients in the Niger Delta ethnic population on efavirenz-based HAART treatment, as the population having homozygous mutant gene or PM are >1% (6%).

Vitamin D as Modulator of Drug Concentrations: A Study on Two Italian Cohorts of People Living with HIV Administered with Efavirenz.

To date, vitamin D seems to have a significant role in affecting the prevention and immunomodulation in COVID-19 disease. Nevertheless, it is important to highlight that this pro-hormone has other several activities, such as affecting drug concentrations, since it regulates the expression of cytochrome P450 (CYP) genes. Efavirenz (EFV) pharmacokinetics is influenced by CYPs, but no data are available in the literature concerning the association among vitamin D levels, seasonality (which affects vitamin D concentrations) and EFV plasma levels. For this reason, the aim of this study was to evaluate the effect of 25-hydroxy vitamin D (25(OH)D3) levels on EFV plasma concentrations in different seasons. We quantified 25(OH)D3 by using chemiluminescence immunoassay, whereas EFV plasma concentrations were quantified with the HPLC–PDA method. A total of 316 patients were enrolled in Turin and Rome. Overall, 25(OH)D3levels resulted in being inversely correlated with EFV concentrations. Some patients with EFV levels higher than 4000 ng/mL showed a deficient 25(OH)D3 concentration in Turin and Rome cohorts and together. EFV concentrations were different in patients without vitamin D supplementation, whereas, for vitamin D-administered individuals, no difference in EFV exposure was present. Concerning seasonality, EFV concentrations were associated with 25(OH)D3 deficiency only in winter and in spring, whereas a significant influence was highlighted for 25(OH)D3 stratification for deficient, insufficient and sufficient values in winter, spring and summer. A strong and inverse association between 25(OH)D3and EFV plasma concentrations was suggested. These data suggest that vitamin D is able to affect drug exposure in different seasons; thus, the achievement of the clinical outcome could be improved by also considering this pro-hormone.

Inter-ethnic genetic variations and novel variant identification in the partial sequences of CYP2B6 gene in Pakistani population.

BackgroundSome single nucleotide polymorphisms (SNPs) in the cytochrome P450 (CYP)2B6 gene lead to decreased enzyme activity and have an impact on drug metabolism. The present study was designed to investigate the patterns of genetic distinction across a hypervariable region of the CYP2B6 gene, known to contain important SNPs, i.e. rs4803419 and rs3745274, among five major ethnic groups of the Pakistani population.MethodsArlequin v3.5.DnaSPv6.12. and network 5 resources were used to analyze population genetic variance in the partial CYP2B6 gene sequences obtained from 104 human samples belonging to Punjabi, Pathan, Sindhi, Seraiki and Baloch ethnicities of Pakistan. The partial CYP2B6 gene region analyzed in the current study is previously known to possess important SNPs.ResultsThe data analyses revealed that genetic variance among samples mainly came from differentiation within the ethnic groups. However, significant genetic variation was also found among the various ethnic groups. The high pairwise Fst genetic distinction was observed between Seraiki and Sindhi ethnic groups (Fst = 0.13392, P-value = 0.026) as well as between Seraiki and Balochi groups (Fst = 0.04303, P-value = −0.0030). However, the degree of genetic distinction was low between Pathan and Punjabi ethnic groups. Some SNPs, including rs3745274 and rs4803419, which are previously shown in strong association with increased plasma Efavirenz level, were found in high frequency. Besides, a novel SNP, which was not found in dbSNP and Ensemble databases, was identified in the Balochi ethnicity. This novel SNP is predicted to affect the CYP2B6 splicing pattern.ConclusionThese results may have significant implications in Pakistani ethnicities in the context of drugs metabolized by CYP2B6, especially in Seraiki and Balochi ethnicity. The novel heterogeneous SNP, found in the present study, might lead to altered drug-metabolizing potential of CYP2B6 and, therefore, may be implicated in non-responder phenomenon.

Influence of SULT1A1*2 Polymorphism on Plasma Efavirenz Concentration in Thai HIV-1 Patients.

PurposePlasma efavirenz (EFV) concentrations within therapeutic levels are essential to successfully treat patients suffering from human immunodeficiency virus (HIV) type 1. In addition to the drug-metabolizing enzyme CYP2B6, other phase II drug-metabolizing enzymes and transporters may have an important role in the pharmacokinetics of EFV. Thus, the influence of phase II drug-metabolizing enzymes and drug transporters on plasma EFV levels was investigated in Thai HIV patients receiving EFV.Patients and MethodsGenotyping was performed by TaqMan® real-time PCR in 149 HIV-infected Thai adults, and plasma efavirenz concentration was measured by a validated high-performance liquid chromatography in 12 hours after dosing steady-state plasma samples at week 12 and 24.ResultsPatients with three or more copies of SULT1A1 had significantly lower median plasma EFV concentrations than those carrying two copies at week 12 (p=0.046) and SULT1A1*2 (c.638G>A) carriers had significantly lower median plasma EFV concentrations compared to those not carrying the variant at week 24 (p=0.048). However, no significant association was found after adjusting for CYP2B6 genotype.ConclusionGenetic variation in a combination of SULT1A1*2 and SULT1A1 copy number may contribute to variability in EFV metabolism and thereby may impact drug response. The influence of a combination between the SULT1A1 and CYP2B6 genotype on EFV pharmacokinetics should be further investigated in a larger study population.

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

Background: The pharmacogenomics and pharmacokinetics/pharmacodynamics of 400mg 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 200mg, efavirenz 400mg andlamivudine) or a standard dose regimen. Relationships between pharmacogenomics and efavirenz pharmacokinetics/pharmacodynamics were explored at 48weeks. 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<60kg had higher efavirenz concentration compared with those with weight ≥60kg when using 600 mgefavirenz, this was not observed with400mg efavirenz. Conclusion: The effect of pharmacogenomics and body weight on the efavirenz concentration was significant in the 600 mggroupbut not in the 400mg group.

Non-nucleoside reverse transcriptase inhibitor levels among HIV-exposed uninfected infants at the time of HIV PCR testing - findings from a tertiary healthcare facility in Pretoria, South Africa.

IntroductionTo date, very little programmatic data has been published regarding serial antiretroviral (ARV) levels in infants exposed to maternal treatment and/or infant prophylaxis during the first months of life. Such data provide the opportunity to describe the proportion of infants exposed to virologically suppressive levels of ARVs and to gauge adherence to the prevention of mother‐to‐child transmission of HIV (PMTCT) programme.MethodsFrom August 2014 to January 2016, HIV‐exposed infants born at Kalafong Provincial Tertiary Hospital in Pretoria, South Africa were enrolled as part of an observational cohort study. Plasma samples from HIV‐exposed uninfected infants were obtained at birth, 6‐weeks, 10‐weeks and 14‐weeks of age and quantitative efavirenz (EFV) and nevirapine (NVP) drug level testing performed using liquid chromatography‐mass spectrometry, irrespective of maternal ARV regimen. Descriptive analysis of EFV and NVP levels in relation to self‐reported maternal and infant ARV exposure was performed. EFV levels >500 ng/mL and NVP levels >100 ng/mL were reported based on studies suggesting that trough levels above these thresholds are associated with virological suppression and PMTCT respectively.ResultsAmong 66 infants exposed to maternal EFV in utero, 29 (44%) had virologically suppressive plasma EFV levels at birth, with a median level of 1665 ng/mL (IQR: 1094 to 3673). Among infants who were exclusively breastfed at 6‐, 10‐ and 14 weeks, 13/48 (27%), 5/25 (25%) and 0/21 (0%) had virologically suppressive EFV levels. Among 64 infants whose mothers reported administering daily infant NVP at time of their 6‐week HIV PCR test, only 45 (70%) had NVP levels above the minimum prophylactic trough level.ConclusionsDuring the first 10‐weeks after delivery, a quarter of breastfed infants born to women on an EFV‐containing treatment regimen maintained virologically suppressive EFV plasma levels. This finding highlights the importance of both careful monitoring of ARV side effects and repeat HIV PCR after the first few months of life among HIV‐exposed uninfected infants. As 30% of infants had inadequate NVP plasma levels at 6‐weeks of age, adherence counselling to caregivers regarding infant prophylaxis needs to be enhanced to further reduce mother‐to‐child transmission of HIV.

Effect of ATP-Binding cassette, Sub-Family B polymorphism on plasma nevirapine and efavirenz levels in human immunodeficiency virus with tuberculosis-infected cases: A molecular structure analysis

Background: Tuberculosis (TB) is an important infection that is usually seen in the patient with underlying human immunodeficiency virus (HIV) infection. An important concern on the cases with HIV/TB is the management of HIV by antiretroviral drug treatment (antiretroviral therapy). The effect of underlying genetic factor is interesting. The effect of adenosine triphosphate-binding cassette, sub-family B (ABCB-1) polymorphism on plasma nevirapine and efavirenz levels is inconclusive. Methods: The authors perform standard molecular structure analysis to assess the effect of C and T alleles of ABCB-1 C3435T polymorphism. The phenotype expressions, reflected by nevirapine and efavirenz levels, are comparatively studied. Results: With focus on 3435 position, the ratio of derived molecular weight after quantum assessment, comparing CC to CT and TT genotypes, is equal to 1:1.068:1.135. Conclusion: The authors can identify the effect of ABCB-1 on the plasma nevirapine and efavirenz levels in HIV/TB patients.

A maintenance 3-day-per-week schedule with the single tablet regimen efavirenz/emtricitabine/tenofovir disoproxil fumarate is effective and decreases sub-clinical toxicity.

Antiretroviral drugs contained in single tablet Atripla have pharmacokinetic properties that could allow for longer than once-daily dosing. We hypothesized that simplifying Atripla once daily to 3-day per week would be feasible, able to maintain viral suppression and less toxic. Virologically suppressed (≥2 years) HIV+ adults on Atripla once daily, CD4 greater than 350 cells/μl at inclusion, and no prior documented virological failure or evidence of resistance mutations to efavirenz, tenofovir, or emtricitabine were randomized to maintain their once-daily (OD) regimen or to reduce it to 3 days (Mondays, Wednesdays, and Fridays) a week (3W) (A-TRI-WEEK pilot trial). Primary end-point was the proportion of patients free of treatment failure (noncompleter = failure) at 24 weeks. CD4 and CD8 cells, ultrasensitive HIV-1 RNA, Pittsburg Sleep Quality Index (PSQI), bone mineral density, plasma efavirenz levels, and fasting blood and urine chemistries were measured at baseline and 24 weeks. The study is registered at ClinicalTrials.gov, NCT01778413. Sixty-one patients were randomized. All patients in both arms remained free of treatment failure (estimated difference 0%; 95% confidence interval -14.1 to 14.1). Ultrasensitive plasma HIV-1 RNA below detection threshold showed no difference between arms (70% in the 3W arm vs. 71% in the OD arm, P = 0.933) at 24 weeks. Total cholesterol and femur T-score significantly increased, whereas PSQI, plasma efavirenz, albumin/creatinine and beta-2-microglobulin in urine significantly decreased in the 3W arm relative to OD arm. The A-TRI-WEEK study represents a proof of concept for the feasibility of three-day per week Atripla maintenance that should be further confirmed in a larger, well powered clinical trial.

A proposed management algorithm for late-onset efavirenz neurotoxicity.

A high proportion of HIV-positive patients in South Africa receive concomitant efavirenz (EFV) and isoniazid (INH) therapy. EFV is metabolised in the liver via CYP2B6, and genetic polymorphism of CYP2B6 is known to result in slowed metabolism of the drug. INH is also metabolised in the liver, causing inhibition of a pathway that plays an important role in slow EFV metabolisers. Concomitant INH use therefore affects plasma levels of EFV. EFV is well known to cause neuropsychiatric side-effects on initiation, and a recent adult case series described late-onset neurotoxicity in the form of subacute ataxia and encephalopathy in patients treated with EFV for a median of 2 years, in association with toxic plasma levels of the drug. We have seen an increase in cases of EFV toxicity presenting to our neurology referral unit. All cases have been in the context of recent initiation of concomitant INH. We therefore conducted a retrospective case record audit to describe these seven cases with the additional advantage of tertiary-level assessment. We outline the clinical features and investigation results, as well as outcomes after EFV was stopped. Our main objectives are to highlight the probable role of concomitant INH use in the development of this syndrome, and to suggest that only limited work-up may be warranted in suspected cases.

A proposed management algorithm for late-onset efavirenz neurotoxicity

A high proportion of HIV-positive patients in South Africa receive concomitant efavirenz (EFV) and isoniazid (INH) therapy. EFV is metabolised in the liver via CYP2B6, and genetic polymorphism of CYP2B6 is known to result in slowed metabolism of the drug. INH is also metabolised in the liver, causing inhibition of a pathway that plays an important role in slow EFV metabolisers. Concomitant INH use therefore affects plasma levels of EFV. EFV is well known to cause neuropsychiatric side-effects on initiation, and a recent adult case series described late-onset neurotoxicity in the form of subacute ataxia and encephalopathy in patients treated with EFV for a median of 2 years, in association with toxic plasma levels of the drug. We have seen an increase in cases of EFV toxicity presenting to our neurology referral unit. All cases have been in the context of recent initiation of concomitant INH. We therefore conducted a retrospective case record audit to describe these seven cases with the additional advantage of tertiary-level assessment. We outline the clinical features and investigation results, as well as outcomes after EFV was stopped. Our main objectives are to highlight the probable role of concomitant INH use in the development of this syndrome, and to suggest that only limited work-up may be warranted in suspected cases.

Cytochrome 2B6 polymorphism and efavirenz-induced central nervous system symptoms : a substudy of the ANRS ALIZE trial.

Single nucleotide polymorphisms in the cytochrome P450 (CYP) 2B6 gene have been associated with high interindividual variation in efavirenz pharmacokinetics. However, clinical data on the relationship of CYP2B6 polymorphisms with the occurrence of efavirenz-induced central nervous system (CNS) symptoms are limited. We analysed four polymorphisms in the CYP2B6 (516 G>T), CYP3A5 (6986 A>G) and ATP-binding cassette, sub-family B, member 1 (ABCB1) (2677 G>T/A and 3435 C>T) genes in HIV-infected adults virologically suppressed on a protease inhibitor-based regimen who switched to a regimen containing emtricitabine, didanosine and efavirenz in the setting of the ANRS ALIZE trial. Kaplan-Meier methods and Cox regression analysis were used to investigate their association with efavirenz plasma levels and CNS events up to 48 months after switching. In total, 191 patients with a median age of 41 years, who were 87% male and 85% Caucasian, were enrolled in the study. Variant allelic frequencies were 0.49, 0.93, 0.59 and 0.63 for CYP2B6 516, CYP3A5 392, ABCB1 2677 and ABCB1 3435, respectively. The median efavirenz plasma concentration (MEPC) was 2.2 mg/L [interquartile range (IQR) 1.7-2.8 mg/L] and was significantly higher in patients with the deficient CYP2B6 516T. Overall, 242 CNS events were reported in 104 individuals (54%). No correlation was found between MEPC and CNS events. The occurrence of a first CNS event was lower in patients with the CYP2B6 516 G/G genotype vs. CYP2B6 516 T genotypes [50% (IQR: 40-60%) vs. 66% (IQR: 56-75%), respectively; P = 0.02]. In an adjusted Cox regression model, there was a tendency towards a higher risk of a first CNS event among carriers of the variant CYP2B6 516 T allele (relative risk 1.4 [95% CI, 0.99-2.1]; P?=?.06), compared with noncarriers. The deficient CYP2B6 516 T allele is associated with higher efavirenz plasma drug levels and more frequent CNS-related symptoms.

Efavirenz pharmacogenetics in a cohort of Italian patients

The pharmacogenetics and pharmacokinetics of efavirenz (EFV) have been widely studied, although data in the Italian population are limited. Single nucleotide polymorphisms (SNPs) in the CYP2B6 gene have been associated with increased EFV plasma concentrations and central nervous system toxicity. The aim of this work was to evaluate EFV plasma exposure according to SNPs in genes involved in drug metabolism and elimination in a cohort of Italian HIV-1-positive patients treated with EFV. Plasma samples were used to measure EFV concentrations at 12h after intake (C12) by a validated HPLC/PDA system. Whole blood was used to identify SNPs in ABCB1, MRP2, CYP2B6, CYP2A6, UGT2B7, NR1I2 (PXR), NR1I3 (CAR) and HNF4α by real-time PCR. The association between SNPs and EFV plasma levels was evaluated through non-parametric tests. Among 201 patients, the median EFV C12 was 2618.5ng/mL. No significant associations were found for MRP2, CYP2A6, UGT2B7, PXR and CAR SNPs; conversely, an association of CYP2B6 516G>T, ABCB1 3435C>T and 2677G>T, and HNF4α 975C>G polymorphisms with EFV C12 was observed. In multivariate analysis, only CYP2B6 516 TT and ABCB1 3435 TT genotypes were independently associated with an EFV C12 of >4000ng/mL (toxicity cut-off). This study confirmed the role of CYP2B6 and ABCB1 polymorphisms, showed a relationship with HNF4α, and the lack of association of CYP2A6, UGT2B7, NR1I2 and NR1I3 SNPs on EFV plasma exposure. Data regarding some of the studied SNPs are the first obtained in an Italian cohort of HIV patients and lead to a global vision about EFV pharmacogenetics.

Inhibition of Efavirenz Metabolism by Sertraline and Nortriptyline and Their Effect on Efavirenz Plasma Concentrations.

Between 22 and 45% of HIV-positive subjects are likely to report symptoms of depression. Considering this background, a potential pharmacokinetic interaction between the nonnucleoside reverse transcriptase inhibitor efavirenz (EFV) and two antidepressants, sertraline (SRT) and nortriptyline (NT), was studied. Rats were administered EFV alone or together with the antidepressants, and changes in the plasma levels and pharmacokinetic parameters of EFV were analyzed. Additional in vitro experiments with rat and human hepatic microsomes were carried out to evaluate the inhibitory effect of SRT and NT on EFV metabolism by determining the formation rate of the major EFV metabolite (8-OH-EFV). In vivo studies showed similar increases in the plasma levels of EFV when it was coadministered with SRT or NT. However, the studies using rat hepatic microsomes showed a more potent inhibitory effect of NT than of SRT on the metabolism of EFV, with values for the 50% inhibition constant (IC50) and inhibitory constant (Ki) for NT about 9-fold lower than those for SRT. An equation was deduced that explains the similar in vivo effects of SRT and NT in spite of the different in vitro performance data. Using human hepatic microsomes, the strongest inhibitory effect was observed with SRT. In summary, pharmacokinetic interactions between EFV, SRT, and NT, associated with the inhibition of hepatic metabolism of EFV, have been detected in rats. Both antidepressants also inhibit EFV metabolism in human hepatic microsomes, but additional in vivo studies in humans are required to evaluate the clinical implication of this interaction.

CYP2B6*6, CYP2B6*18, Body weight and sex are predictors of efavirenz pharmacokinetics and treatment response: population pharmacokinetic modeling in an HIV/AIDS and TB cohort in Zimbabwe.

BackgroundEfavirenz (EFV) therapeutic response and toxicity are associated with high inter-individual variability attributed to variation in its pharmacokinetics. Plasma concentrations below 1 μg/ml may result in virologic failure and above 4 μg/ml, may result in central nervous system adverse effects. This study used population pharmacokinetics modeling to explore the influence of demographic and pharmacogenetic factors including efavirenz-rifampicin interaction on EFV pharmacokinetics, towards safer dosing of EFV.MethodsPatients receiving an EFV-based regimen for their antiretroviral therapy and a rifampicin-containing anti-TB regimen were recruited. EFV plasma concentrations were measured by HPLC and genomic DNA genotyped for variants in the CYP2B6, CYP2A6 and ABCB1 genes. All patients were evaluated for central nervous system adverse effects characterised as sleep disorders, hallucinations and headaches using the WHO ADR grading system. A pharmacokinetic model was built in a forward and reverse procedure using nonlinear mixed effect modeling in NONMEM VI followed by model-based simulations for optimal doses.ResultsCYP2B6*6 and *18 variant alleles, weight and sex were the most significant covariates explaining 55% of inter-individual variability in EFV clearance. Patients with the CYP2B6*6TT genotype had a 63% decrease in EFV clearance despite their CYP2B6*18 genotypes with females having 22% higher clearance compared to males. There was a 21% increase in clearance for every 10 kg increase in weight. The effect of TB/HIV co-treatment versus HIV treatment only was not statistically significant. No clinically relevant association between CYP2B6 genotypes and CNS adverse effects was seen, but patients with CNS adverse effects had a 27% lower clearance compared to those without. Model- based simulations indicated that all carriers of CYP2B6*6 TT genotype would be recommended a dose reduction to 200 mg/day, while the majority of extensive metabolisers may be given 400 mg/day and still maintain therapeutic levels.ConclusionThis study showed that screening for CYP2B6 functional variants has a high predictability for efavirenz plasma levels and could be used in prescribing optimal and safe EFV doses.

Prevalence of CYP2B6 polymorphisms in Argentinians: the role of genetic testing.

CYP2B6 is a highly polymorphic isoenzyme involved in the metabolism of many drugs including cyclophosphamide, bupropion, and efavirenz. A single nucleotide polymorphism (SNP) in CYP2B6 (516G>T) resulted in decreased expression and function associated with the CYP2B6*6 haplotype. Among the clinical implications of this phenotype, decreased activation of cyclophosphamide and increased plasma levels of efavirenz associated with increased central nervous system toxicity have been reported. The frequency of the CYP2B6 (516G>T) SNP has been studied in several different populations, but there is no data regarding distribution among Argentinians. In this study, 102 DNA samples from healthy volunteers were analyzed using a polymerase chain reaction-restriction fragment length polymorphism reaction specific for the CYP2B6 (516G>T) SNP. Our results showed a prevalence of 71.08% for the G allele and 28.92% for the T allele. This was distributed as 52.9% for the GG genotype (reduced dosage required), 36.6% for the GT genotype (normal dosage range), and 10.8% for the TT genotype (high drug toxicity). There was no preferential gender distribution observed. The relatively high prevalence of the TT genotype in our population supports the clinical use of genotyping as an additional tool in personalized medicine.

Can antiretroviral therapy be tailored to each human immunodeficiency virus-infected individual? Role of pharmacogenomics.

Pharmacogenetics refers to the effect of single nucleotide polymorphisms (SNPs) within human genes on drug therapy outcome. Its study might help clinicians to increase the efficacy of antiretroviral drugs by improving their pharmacokinetics and pharmacodynamics and by decreasing their side effects. HLAB*5701 genotyping to avoid the abacavir-associated hypersensitivity reaction (HSR) is a cost-effective diagnostic tool, with a 100% of negative predictive value, and, therefore, it has been included in the guidelines for treatment of human immunodeficiency virus (HIV) infection. HALDRB*0101 associates with nevirapine-induced HSR. CYP2B6 SNPs modify efavirenz plasma levels and their genotyping help decreasing its central nervous system, hepatic and HSR toxicities. Cytokines SNPs might influence the development of drug-associated lipodystrophy. APOA5, APOB, APOC3 and APOE SNPs modify lipids plasma levels and might influence the coronary artery disease risk of HIV-infected individuals receiving antiretroviral therapy. UGT1A1*28 and ABCB1 (MDR1) 3435C > T SNPs modify atazanavir plasma levels and enhance hyperbilirubinemia. Much more effort needs to be still devoted to complete large prospective studies with multiple SNPs genotyping in order to reveal more clues about the role played by host genetics in antiretroviral drug efficacy and toxicity.

A 30-years review on pharmacokinetics of antibiotics: is the right time for pharmacogenetics?

Drug bioavailability may vary greatly amongst individuals, affecting both efficacy and toxicity: in humans, genetic variations account for a relevant proportion of such variability. In the last decade the use of pharmacogenetics in clinical practice, as a tool to individualize treatment, has shown a different degree of diffusion in various clinical fields.In the field of infectious diseases, several studies identified a great number of associations between host genetic polymor-phisms and responses to antiretroviral therapy. For example, in patients treated with abacavir the screening for HLA-B*5701 before starting treatment is routine clinical practice and standard of care for all patients; efavirenz plasma levels are influenced by single nucleotide polymorphism (SNP) CYP2B6-516G> T (rs3745274). Regarding antibiotics, many studies investigated drug transporters involved in antibiotic bioavailability, especially for fluoroquinolones, cephalosporins, and antituberculars. To date, few data are available about pharmacogenetics of recently developed antibiotics such as tigecycline, daptomycin or linezolid. Considering the effect of SNPs in gene coding for proteins involved in antibiotics bioavailability, few data have been published. Increasing knowledge in the field of antibiotic pharmacogenetics could be useful to explain the high drug inter-patients variability and to individualize therapy. In this paper we reported an overview of pharmacokinetics, pharmacodynamics, and pharmacogenetics of antibiotics to underline the importance of an integrated approach in choosing the right dosage in clinical practice.

The role of genetic polymorphisms in cytochrome P450 and effects of tuberculosis co-treatment on the predictive value of CYP2B6 SNPs and on efavirenz plasma levels in adult HIV patients

Efavirenz (EFV) exhibits interindividual pharmacokinetic variability caused by differences in cytochrome P450 (CYP) expression. Most tuberculosis (TB) drugs interact with the CYP metabolizing enzymes, while the clinical validity of genotyping in predicting EFV plasma levels in Rwandan subjects is not known. We investigated in patients co-infected with human immunodeficiency virus (HIV) and TB recruited in Rwanda the effects of 10 SNPs in five drug-metabolizing enzymes on EFV plasma levels and treatment response when patients are treated with EFV-containing therapy alone (n=28) and when combined with rifampicin-based TB treatment (n=62), and the validity of genotyping for CYP2B6 single nucleotide polymorphisms in predicting supra-therapeutic EFV levels. There was a significant difference between CYP1A2 −739T/G and T/T genotypes when patients were treated with EFV-containing therapy combined with rifampicin-based TB treatment, but not when EFV-containing therapy was alone. CYP2B6 516T/T genotype was associated with high EFV levels compared to other CYP2B6 516G>T genotypes in the presence and in the absence of rifampicin-based TB treatment. Predictive factors of EFV plasma levels in the presence of rifampicin-based TB treatment were CYP2A6 1093G>A, CYP2B6 516G>T, and CYP2B6 983T>C accounting for 27%, 43%, and 29% of the total variance in EFV levels, respectively. There was a high positive predictive value (PPV) (100%) for CYP2B6 516T/T and 983T/T genotypes in predicting EFV plasma levels above the therapeutic range, but this PPV decreased in the presence of rifampicin-based TB treatment. Rifampicin-based TB treatment was also shown to affect EFV plasma levels significantly, but did not affect the significant reduction of HIV-RNA copies. These results indicate that genotyping for CYP2B6 SNPs could be used as a tool in predicting supra-therapeutic EFV plasma levels, which could minimize adverse drug events.