Pharmacokinetic/pharmacodynamic investigation of raltegravir with or without lamivudine in the context of HIV-1 pre-exposure prophylaxis (PrEP).

BACKGROUND: To characterize their potential use in pre-exposure prophylaxis (PrEP) we compared the pharmacokinetics of raltegravir and lamivudine in genital tissue against ex vivo tissue infection with HIV-1. METHODS: Open-label trial of 36 HIV-negative females and males randomized to 7 days raltegravir 400 mg twice daily and 7 days raltegravir 400 mg+lamivudine 150 mg twice daily (after washout), or vice versa. Blood, saliva, rectal fluid, rectal tissue, vaginal fluid and vaginal tissue were sampled at baseline and on and off PrEP during a total of 12 days, for pharmacokinetics and antiviral activity via ex vivo HIV-1BaL challenge. Ex vivo infectivity was compared with baseline. The trial has been registered in https://clinicaltrials.gov/ with the identifier NCT03205566. RESULTS: Steady state for both drugs was reached by day 4. Dosing with raltegravir alone provided modest ex vivo HIV protection with higher drug levels in rectal tissue and vaginal tissue than in plasma on and off PrEP. Off PrEP, plasma and vaginal concentrations declined rapidly, while persisting in the rectum. On PrEP, the highest lamivudine concentrations were in the rectum, followed by vaginal tissue then plasma. Lamivudine washout was rapid in plasma, while persisting in the rectum and vagina. Raltegravir/lamivudine increased ex vivo protection on and off PrEP compared with raltegravir alone, reaching maximum protection at day 2 in rectal tissue and at day 8 in vaginal tissue. CONCLUSIONS: Raltegravir 400 mg+lamivudine 150 mg showed high levels of ex vivo HIV protection, associated with high drug concentrations persisting after discontinuation in vaginal and rectal compartments, supporting further investigation of these agents for PrEP.

AUTOSTERE: Systematic Search for Scaffold Replacement Opportunities within Structural Databases.

Medicinal chemists often bias toward working with scaffolds with which previously they have had direct experience and successes. In this way, it is often the case that scaffolds which have proven tractable within a research group are "reused" across multiple and sometimes unrelated drug targets. With this concept in mind, we designed a new computer algorithm AUTOSTERE which could systematically assess the opportunities to replace any part of any molecule within an entire database of known ligand structures with a target scaffold and automatically evaluate the potential designs in the context of the original ligand's protein environment. As such, it performs scaffold replacement on an unprecedented scale and suggests new target opportunities for preferred chemistries rather than the conventional reverse situation. The results of this approach for one scaffold, a substituted triazolinone, applied to a set of 10 426 ligand conformations extracted from the PDB are described. This led to the identification of ∼600 novel ligands incorporating the triazolinone scaffolds in complex with their predicted drug targets. From these, design examples are provided for HSP-90, cathepsin K, and TIE-2 kinase. A further study involved the searching for possible drug targets for unusual pyridopyrimidine cores. This process resulted in the identification of potential novel HIV reverse transcriptase inhibitors which were synthesized and shown to exhibit similar in vitro potencies to marketed compounds. Overall, the methodology described provides a powerful new approach to identify new target opportunities for scaffolds of provenance.

A Population Pharmacokinetic Analysis Shows that Arylacetamide Deacetylase (AADAC) Gene Polymorphism and HIV Infection Affect the Exposure of Rifapentine.

Rifapentine is a rifamycin used to treat tuberculosis. As is the case for rifampin, plasma exposures of rifapentine are associated with the treatment response. While concomitant food intake and HIV infection explain part of the pharmacokinetic variability associated with rifapentine, few studies have evaluated the contribution of genetic polymorphisms. We evaluated the effects of functionally significant polymorphisms of the genes encoding OATP1B1, the pregnane X receptor (PXR), constitutive androstane (CAR), and arylacetamide deacetylase (AADAC) on rifapentine exposure. Two studies evaluating novel regimens among southern African patients with drug-susceptible pulmonary tuberculosis were included in this analysis. In the RIFAQUIN study, rifapentine was administered in the continuation phase of antituberculosis treatment in 1,200-mg-once-weekly or 900-mg-twice-weekly doses. In the Daily RPE study, 450 or 600 mg was given daily during the intensive phase of treatment. Nonlinear mixed-effects modeling was used to describe the pharmacokinetics of rifapentine and to identify significant covariates. A total of 1,144 drug concentration measurements from 326 patients were included in the analysis. Pharmacogenetic information was available for 162 patients. A one-compartment model with first-order elimination and transit compartment absorption described the data well. In a typical patient (body weight, 56 kg; fat-free mass, 45 kg), the values of clearance and volume of distribution were 1.33 liters/h and 25 liters, respectively. Patients carrying the AA variant (65.4%) of AADAC rs1803155 were found to have a 10.4% lower clearance. HIV-infected patients had a 21.9% lower bioavailability. Once-weekly doses of 1,200 mg were associated with a reduced clearance (13.2%) compared to that achieved with more frequently administered doses. Bioavailability was 23.3% lower among patients participating in the Daily RPE study than in those participating in the RIFAQUIN study. This is the first study to report the effect of AADAC rs1803155AA on rifapentine clearance. The observed increase in exposure is modest and unlikely to be of clinical relevance. The difference in bioavailability between the two studies is probably related to the differences in food intake concomitant with the dose. HIV-coinfected patients had lower rifapentine exposures.

Validation and clinical application of a novel LC-MS method for quantification of dolutegravir in breast milk.

Aim: A novel, sensitive and reproducible method for quantification of dolutegravir (DTG) in dried breast milk spots (DBMS) was developed and validated for use in clinical studies. Its application enabled measurement of DTG pharmacokinetics in breastfeeding mothers and their infants. Results/methodology: Sample extraction was by liquid-liquid extraction using tert-butyl methy-ether, with DTG-d5 as an internal standard. DTG was eluted on a reverse phase C18 Waters XBridge (3.5 µm: 2.1 × 50 mm) column using a gradient mobile phase consisting of 0.1% formic acid in deionised water or methanol. The assay was validated over a calibration range of 10-4000 ng/ml. Conclusion: Stability, inter and intra-assay variability were acceptable according to FDA and EMA bioanalytical method guidelines. The assay is robust, accurate, precise and can be reliably applied for analysis of clinical samples in trials from low resource settings.

Polymorphisms of tenofovir disoproxil fumarate transporters and risk of kidney tubular dysfunction in HIV-positive patients: genetics of tenofovir transporters.

The association between single nucleotide polymorphisms of genes encoding transport proteins involved in the bio-disposition of tenofovir disoproxil fumarate (TDF) and kidney tubular dysfunction (KTD) in HIV-positive patients was examined in this study. Fifty-eight patients who received TDF were screened for KTD using retinol-binding protein (RBP) concentration in urine. We defined KTD as the top quartile of urinary RBP/creatinine ratio (>17 µg/mmol), regardless of estimated glomerular filtration rate (eGFR) or proteinuria. Genotyping of genes encoding transport proteins involved in the disposition of TDF was undertaken using validated Taqman 5' nuclease assays. Patients with KTD (N = 15) had higher current CD4 cell counts, lower eGFR and were less likely to possess the genotype CC at position 24 of the ABBC2 (MRP2, rs717620) gene. In multivariate analysis, genotype CC at position 24 of the ABBC2 gene was significantly associated with KTD (odds ratio =0.05, 95% confidence interval = 0.003-0.7, P = 0.027). Genotype CC at position 24 of the ABBC2 (MRP2 rs717620) gene was significantly associated with a reduced risk of elevated urinary RBP in HIV-positive patients exposed to TDF.

Genetic Determinants of the Pharmacokinetic Variability of Rifampin in Malawian Adults with Pulmonary Tuberculosis.

Variable exposure to antituberculosis (TB) drugs, partially driven by genetic factors, may be associated with poor clinical outcomes. Previous studies have suggested an influence of the SLCO1B1 locus on the plasma area under the concentration-time curve (AUC) of rifampin. We evaluated the contribution of single nucleotide polymorphisms (SNPs) in SLCO1B1 and other candidate genes (AADAC and CES-1) to interindividual pharmacokinetic variability in Malawi. A total of 174 adults with pulmonary TB underwent sampling of plasma rifampin concentrations at 2 and 6 h postdose. Data from a prior cohort of 47 intensively sampled, similar patients from the same setting were available to support population pharmacokinetic model development in NONMEM v7.2, using a two-stage strategy to improve information during the absorption phase. In contrast to recent studies in South Africa and Uganda, SNPs in SLCO1B1 did not explain variability in AUC0-∞ of rifampin. No pharmacokinetic associations were identified with AADAC or CES-1 SNPs, which were rare in the Malawian population. Pharmacogenetic determinants of rifampin exposure may vary between African populations. SLCO1B1 and other novel candidate genes, as well as nongenetic sources of interindividual variability, should be further explored in geographically diverse, adequately powered cohorts.

Brief Report: Pharmacokinetic/Pharmacodynamic Investigation of Single-Dose Oral Maraviroc in the Context of HIV-1 Pre-exposure Prophylaxis.

To investigate the pharmacokinetics/pharmacodynamics of single-dose maraviroc 300 mg in HIV-1 exposure compartments. Maraviroc concentrations in blood, secretions (vaginal, urethral, oral, and rectal), and tissue (vaginal and rectal) were measured, and ex vivo challenge was performed in 54 healthy volunteers to study protection from HIV infection. Maraviroc Cmax occurred within 4 hours in most compartments. Concentrations from 4 to 72 hours were above intracellular (IC) IC90 in all compartments, range 15-8095 ng/mL. Mean AUC0-72 compartment-to-plasma ratios were highest in the rectum (45-819) and urethra (144) compared with the female genital tract (1.6-4.8) and saliva (0.2). No sex differences in AUC0-72 or Cmax were observed. No ex vivo protection from HIV-1BaL occurred in rectal or vaginal tissue. Despite high and sustained concentrations, single-dose maraviroc was not protective against ex vivo challenge of vaginal/rectal tissue.

Cytotoxic chemotherapy and the evolution of cellular and viral resistance to antiretroviral therapy in HIV- infected individuals with lymphoma.

BACKGROUND: The use of combination antiretroviral therapy (cART) and cytotoxic chemotherapy for HIV-associated lymphoma runs the risks of inducing HIV drug resistance. This study examined two possible mechanisms: altered expression of membrane drug transporter protein (MTP) and acquisition of mutations in pro-viral DNA. METHODS: Expression levels of MTP and pro-viral DNA resistance mutation analysis were performed on peripheral blood mononuclear cells (PBMC) before, during, and after chemotherapy. RESULTS: Twenty nine patients completed the three time point estimations. There were no significant variations before, during, and after chemotherapy in the expression of four MTPs: ABCB1, ABCC1, ABCC2, and SLCO3A1 (OATP3A1). Pro-viral DNA sequencing revealed that only one patient developed a new nucleos/tide reverse transcriptase inhibitor-associated mutation (184V) during the course of the study, giving a mutation rate of 0.0027 per person per year. CONCLUSIONS: In conclusion, concomitant administration of cytotoxic chemotherapy and cART does not induce expression of MTP. Furthermore, no significant changes in viral resistance were observed pre- and post-chemotherapy, suggesting mutagenic cytotoxic chemotherapy seems not to induce mutations in HIV pro-viral DNA.

The development and application of a novel LC-MS/MS method for the measurement of Dolutegravir, Elvitegravir and Cobicistat in human plasma.

Dolutegravir and Elvitegravir belongs to a class of integrase inhibitors which has recently been approved by the FDA for the treatment of HIV-infection. Elvitegravir and its co-administered booster drug, Cobicistat, has shown the potential to be a candidate for a one pill once a day regimen and is currently a component of many clinical trials. A sensitive LC-MS/MS method has been developed and validated for the simultaneous determination of these three drugs in human plasma. A liquid- liquid extraction was used as a sample preparation technique using 100µL of plasma. The method was validated from 10 to 4000ng/mL for Dolutegravir, Elvitegravir and Cobicistat. Chromatography was performed on XBridge C18 2.1mm×50mm column, using an 80:20 methanol/water mobile phase containing 0.1% formic acid on a gradient program. This method was successfully applied for ongoing clinical trials.

Comprehensive Pharmacokinetic, Pharmacodynamic and Pharmacogenetic Evaluation of Once-Daily Efavirenz 400 and 600 mg in Treatment-Naïve HIV-Infected Patients at 96 Weeks: Results of the ENCORE1 Study.

BACKGROUND: ENCORE1 demonstrated non-inferiority of daily efavirenz 400 mg (EFV400) versus 600 mg (EFV600) to 96 weeks in treatment-naïve, HIV-infected adults but concerns regarding lower EFV400 concentrations remained. Therefore, relationships between EFV pharmacokinetics (PK) and key genetic polymorphisms with 96-week efficacy and safety were investigated. METHODS: Relationships between EFV PK parameters and single nucleotide polymorphisms (SNP; CYP2B6, CYP2A6, CYP3A4, NR1I3, NR1I2, ABCB1) with plasma HIV-RNA (pVL) <200 copies/mL and EFV discontinuation and adverse events at 96 weeks were explored. Receiver operating characteristic curve analysis evaluated the predictability of mid-dose interval (C12) cutoffs and 96-week pVL. RESULTS: A total of 606 patients (32 % female; 37 % African, 33 % Asian; n = 311 EFV400, n = 295 EFV600) were included. EFV PK parameters, including C12, were not associated with pVL <200 copies/mL at 96 weeks (odds ratio [OR] 5.25, 95 % confidence interval [CI] 0.41-67.90, p = 0.204). Lower risk of CNS-related adverse events was associated with CYP2B6 983TC/CC (OR 0.35, 95 % CI 0.15-0.81, p = 0.015) and higher risk was associated with CYP2B6 15582CT/TT and ABCB1 3435TT (OR 1.46, 95 % CI 1.02-2.09, p = 0.040; OR 2.31, 95 % CI 1.33-4.02, p = 0.003, respectively). Discontinuation due to adverse events (clinician decision) was independently associated with dose (OR 2.54, 95 % CI 1.19-5.43, p = 0.016). C12 between 0.47 and 0.76 mg/L provided sensitivity/specificity >90 % (100 %/92.3 to 98.9 %/92.3 %) for achieving pVL <200 copies/mL at 96 weeks. CONCLUSIONS: A higher rate of EFV-related adverse events and discontinuations due to these events for EFV600 were not driven by polymorphisms assessed. Although a single threshold concentration associated with HIV suppression may be clinically useful, it was not viable for ENCORE1. Implementation of EFV400 would improve toxicity management whilst still maintaining good efficacy.

Effect of SLCO1B1 Polymorphisms on Rifabutin Pharmacokinetics in African HIV-Infected Patients with Tuberculosis.

Rifabutin, used to treat HIV-infected tuberculosis, shows highly variable drug exposure, complicating dosing. Effects of SLCO1B1 polymorphisms on rifabutin pharmacokinetics were investigated in 35 African HIV-infected tuberculosis patients after multiple doses. Nonlinear mixed-effects modeling found that influential covariates for the pharmacokinetics were weight, sex, and a 30% increased bioavailability among heterozygous carriers of SLCO1B1 rs1104581 (previously associated with low rifampin concentrations). Larger studies are needed to understand the complex interactions of host genetics in HIV-infected tuberculosis patients. (This study has been registered at ClinicalTrials.gov under registration no. NCT00640887.).

Effect of intermittent rifampicin on the pharmacokinetics and safety of raltegravir.

OBJECTIVES: Previous studies of raltegravir and rifampicin have not studied the interaction when rifampicin is dosed intermittently. This study aimed to assess the pharmacokinetics of twice daily raltegravir and intermittently dosed rifampicin. METHODS: This was a prospective, open, single-arm, three-part, controlled study in healthy volunteers. Over a period of 38 days subjects received 5 days of standard-dose raltegravir (400 mg twice daily) followed by 28 days of standard-dose raltegravir plus rifampicin three times a week followed by 5 days of high-dose (800 mg twice daily) raltegravir plus rifampicin three times a week. Pharmacokinetic sampling was performed on days 5, 33 and 38. Raltegravir pharmacokinetic parameters were determined by non-compartmental analysis and reported as geometric means and 90% CIs. ClinicalTrials.gov: NCT01424826. RESULTS: Sixteen subjects (12 females) completed the study. Raltegravir trough plasma concentration (C12) was significantly lower in the presence of rifampicin when dosed at 400 mg twice daily (40%), which was not observed with 800 mg twice daily dosing. Raltegravir Cmax and AUC0-12 were both significantly higher in the presence of rifampicin when dosed at 800 mg twice daily (76% and 84%, respectively), but this dose was well tolerated. CONCLUSIONS: This study suggests that rifampicin induction of raltegravir is comparable between daily and intermittent rifampicin. In the absence of definitive clinical efficacy data to suggest otherwise, doses of 800 mg of raltegravir twice daily with rifampicin thrice weekly are well tolerated and yield higher AUCs and comparable C12 when compared with raltegravir alone.

Quantification of rilpivirine in human plasma, cervicovaginal fluid, rectal fluid and genital/rectal mucosal tissues using liquid chromatography-tandem mass spectrometry.

BACKGROUND: A sensitive, specific and robust liquid chromatography-tandem mass spectrometry method has been developed and validated for the quantification of rilpivirine in human plasma, genital/rectal biofluids and mucosal tissues. METHODS: Plasma and tissue samples were extracted using protein precipitation (acetonitrile/water; 5:1 v/v), and genital/rectal biofluids absorbed onto ophthalmic swabs were extracted using liquid-liquid extraction (hexane/ethyl acetate; 80:20 v/v). A stable isotope-labeled internal standard ((13)C-d4-RPV) was used, and the assay was validated over a concentration range of 0.5-400 ng/ml. CONCLUSION: Inter- and intra-assay precision and accuracy met the acceptance as per US FDA bioanalytical guidelines. The validated assay has been used for the determination of rilpivirine concentrations in these matrices as part of an exploratory pharmacokinetic study investigating the suitability of a long-acting formulation of rilpivirine for pre-exposure prophylaxis.

CYP3A4*22 (c.522-191 C>T; rs35599367) is associated with lopinavir pharmacokinetics in HIV-positive adults.

The CYP3A4*22 (c.522-191 C>T; rs35599367) single nucleotide polymorphism has been associated with lower CYP3A4 mRNA expression and activity. We investigated the association of CYP3A4*22 with the pharmacokinetics of lopinavir through a population pharmacokinetic approach. The minor allele frequency for CYP3A4*22 was 0.035, and seven of 375 patients had a combination of CYP3A4*22 and SLCO1B1 521T>C alleles. Lack of information on the ethnicity in this cohort should be considered as a limitation. However, in the final model, the population clearance was 5.9 l/h and patients with CYP3A4*22/*22 had 53% (P=0.023) lower clearance compared with noncarriers. In addition, the combined effect of CYP3A4*22 with SLCO1B1 521T>C (previously shown to be associated with lopinavir plasma concentration) was analysed. We observed a 2.3-fold higher lopinavir trough concentration (Ctrough) in individuals with CYP3A4*22/*22, a 1.8-fold higher Ctrough with SLCO1B1 521CC and a 9.7-fold higher Ctrough in individuals homozygous for both single nucleotide polymorphisms, compared with noncarriers. A simulated dose-reduction scenario showed that 200/100 mg lopinavir/ritonavir was adequate to achieve therapeutic concentration in individuals with CYP3A4*22/*22 alone or in combination with SLCO1B1 521CC. These data further our understanding of the genetic basis for variability in the pharmacokinetics of lopinavir.

Pharmacogenetic associations with plasma efavirenz concentrations and clinical correlates in a retrospective cohort of Ghanaian HIV-infected patients.

OBJECTIVES: Efavirenz is widely used in first-line antiretroviral therapy in sub-Saharan Africa. However, exposure to efavirenz shows marked interindividual variability that is genetically mediated with potential for important pharmacodynamic consequences. The aims of this study were to assess the frequencies of CYP2B6, CYP2A6, UGT2B7 and CAR single nucleotide polymorphisms (SNPs) and their impact on plasma efavirenz concentration and clinical/immunological responses in Ghanaian patients. METHODS: Genomic DNA from 800 HIV-infected patients was genotyped for selected SNPs by real-time PCR-based allelic discrimination. Mid-dose plasma efavirenz concentrations were measured for 521 patients using HPLC with UV detection. Clinical outcomes in 299 patients on efavirenz were retrospectively assessed. Univariate and multivariate linear regression were performed using best subset selection. Time-to-event outcomes were analysed using a Cox proportional hazards regression model. RESULTS: The variant allele frequencies for CYP2B6 516G>T (rs3745274), CYP2B6 983T>C (rs28399499), CYP2A6 -48T>G (CYP2B6*9B; rs28399433), UGT2B7 802C>T (UGT2B7*2; rs7439366), UGT2B7 735A>G (UGT2B7*1c; rs28365062) and CAR 540C>T (rs2307424) were 48%, 4%, 3%, 23%, 15% and 7%, respectively. CYP2B6 516G>T, CYP2B6 983T>C and CYP2A6 -48T>G were associated with significantly elevated efavirenz concentrations. A trend towards association between plasma efavirenz concentration and CAR 540C>T was observed. CYP2B6 516G homozygosity was associated with immunological failure [adjusted hazards ratio compared with T homozygosity, 1.70 (1.04-2.76); P = 0.03]. CONCLUSIONS: CYP2B6 and CYP2A6 SNPs were associated with higher plasma efavirenz concentrations due to reduction in major and minor phase I routes of elimination, respectively. Further prospective studies are needed to validate the pharmacodynamic correlates of these polymorphisms in this population.

Estimation of the effect of SLCO1B1 polymorphisms on lopinavir plasma concentration in HIV-infected adults.

BACKGROUND: The organic anion transporting polypeptides (OATP)/SLCO family represents an important class of hepatic drug uptake transporters that mediate the sodium independent transport of a diverse range of amphipathic organic compounds, including the protease inhibitors. The SLCO1B1 521T>C (rs4149056) single nucleotide polymorphism (SNP) has been consistently associated with reduced transport activity in vivo, and we previously showed an association of this polymorphism with lopinavir plasma concentrations. The aim of this study was to develop a population pharmacokinetic (PK) model to quantify the impact of 521T>C. METHODS: A population PK analysis was performed with 594 plasma samples from 375 patients receiving lopinavir/ritonavir. Non-linear mixed effects modelling was applied to explore the effects of SLCO1B1 521T>C and patient demographics. Simulations of the lopinavir concentration profile were performed with different dosing regimens considering the different alleles. RESULTS: A one-compartment model with first-order absorption best described the data. Population clearance was 5.67 l/h with inter-patient variability of 37%. Body weight was the only demographic factor influencing clearance, which increased 0.5 l/h for every 10 kg increase. Homozygosity for the C allele was associated with a 37% lower clearance, and 14% for heterozygosity, which were statistically significant. CONCLUSIONS: These data show an association between SLCO1B1 521T>C and lopinavir clearance. The association is likely to be mediated through reduced uptake by hepatocytes leading to higher plasma concentrations of lopinavir. Further studies are now required to confirm the association and to assess the influence of other polymorphisms in the SLCO family on lopinavir PK.

IFN-γ 874A>T genotype is associated with higher CCR5 expression in peripheral blood mononuclear cells from HIV+ patients.

We previously showed that certain cytokines impact on the expression of drug transporters and chemokine receptors in peripheral blood mononuclear cells. Known single-nucleotide polymorphism genes in the genes encoding interferon γ (874A>T, rs62559044) and interleukin 2 (-330T>G, rs2069763) were genotyped in 66 HIV+ patients, and the impact of single-nucleotide polymorphisms on expression of ABCB1, ABCC1, ABCC2, CXCR4, and CCR5 in peripheral blood mononuclear cells from HIV+ patients was assessed. The IFN-γ 874A>T allele and viral load were independently associated with CCR5 expression in patients. These associations have potential implications for HIV disease progression and treatment response that now warrant further study.

Cytochrome P450 2B6 (CYP2B6) and constitutive androstane receptor (CAR) polymorphisms are associated with early discontinuation of efavirenz-containing regimens.

OBJECTIVES: Cytochrome P450 2B6 (CYP2B6) is responsible for the metabolic clearance of efavirenz and single nucleotide polymorphisms (SNPs) in the CYP2B6 gene are associated with efavirenz pharmacokinetics. Since the constitutive androstane receptor (CAR) and the pregnane X receptor (PXR) correlate with CYP2B6 in liver, and a CAR polymorphism (rs2307424) and smoking correlate with efavirenz plasma concentrations, we investigated their association with early (<3 months) discontinuation of efavirenz therapy. METHODS: Three hundred and seventy-three patients initiating therapy with an efavirenz-based regimen were included (278 white patients and 95 black patients; 293 male). DNA was extracted from whole blood and genotyping for CYP2B6 (516G → T, rs3745274), CAR (540C → T, rs2307424) and PXR (44477T → C, rs1523130; 63396C → T, rs2472677; and 69789A → G, rs763645) was conducted. Binary logistic regression using the backwards method was employed to assess the influence of SNPs and demographics on early discontinuation. RESULTS: Of the 373 patients, 131 withdrew from therapy within the first 3 months. Black ethnicity [odds ratio (OR) = 0.27; P = 0.0001], CYP2B6 516TT (OR = 2.81; P = 0.006), CAR rs2307424 CC (OR = 1.92; P = 0.007) and smoking status (OR = 0.45; P = 0.002) were associated with discontinuation within 3 months. CONCLUSIONS: These data indicate that genetic variability in CYP2B6 and CAR contributes to early treatment discontinuation for efavirenz-based antiretroviral regimens. Further studies are now required to define the clinical utility of these associations.

The SLCO1B1 rs4149032 polymorphism is highly prevalent in South Africans and is associated with reduced rifampin concentrations: dosing implications.

Among patients with tuberculosis, rifampin plasma concentrations and sputum conversion rates have been reported to be lower in Africans. Rifampin is a substrate of P-glycoprotein (coded for by the ABCB1 gene) and organic anion-transporting polypeptide 1B1 (coded for by SLCO1B1). The objectives were to identify genetic polymorphisms of drug transporters and the transcriptional regulators pregnane X receptor (PXR) and constitutive androstane receptor (CAR) with an impact on rifampin pharmacokinetics in South Africans. Fifty-seven patients with tuberculosis from Cape Town underwent pharmacokinetic sampling during treatment with rifampin, pyrazinamide, isoniazid, and ethambutol. DNA was genotyped for ABCB1, SLCO1B1, PXR, and CAR polymorphisms by using real-time PCR. NONMEM was used for data analysis. The allele frequency of the SLCO1B1 rs4149032 polymorphism was 0.70. Patients heterozygous and homozygous for this polymorphism had reductions in the bioavailability (and, thus, the area under the curve [AUC]) of rifampin of 18% and 28%, respectively. Simulations showed that increasing the daily rifampin dose by 150 mg in patients with the polymorphism would result in plasma concentrations similar to those of wild-type individuals and reduce the percentage of patients with peak plasma concentrations (C(max)) below 8 mg/liter from 63% to 31%. ABCB1, PXR, and CAR polymorphisms were not associated with differences in rifampin pharmacokinetics. SLCO1B1 rs4149032 was present in most patients and was associated with substantially reduced rifampin exposure. These data suggest that the standard recommended dose of rifampin should be reconsidered for South Africans.

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

BACKGROUND: Nevirapine is metabolized by CYP2B6 and polymorphisms within the CYP2B6 gene partly explain inter-patient variability in pharmacokinetics. The aim of this study was to model the complex relationship between nevirapine exposure, weight and genetics (based on combined analysis of CYP2B6 516G > T and 983T > C single nucleotide polymorphisms). METHODS: Non-linear mixed-effects modelling was used to estimate pharmacokinetic parameters from 275 patients. Simulations of the nevirapine concentration profile were performed with dosing regimens of 200 mg twice daily and 400 mg once daily for individuals with body weights of 50, 70 and 90 kg in combination with CYP2B6 genetic variation. RESULTS: A one-compartment model with first-order absorption best described the data. Population clearance was 3.5 L/h with inter-patient variability of 24.6%. 516T homozygosity and 983C heterozygosity were associated with 37% and 40% lower clearance, respectively. Body weight was the only significant demographic factor influencing clearance, which increased by 5% for every 10 kg increase. For individuals with higher body weight, once-daily nevirapine was associated with a greater risk of sub-therapeutic drug exposure than a twice-daily regimen. This risk was offset in individuals who were 516T homozygous or 983C heterozygous in which drug exposure was optimal for  >  95% of patients with body weight of ≤ 70 kg. CONCLUSIONS: The data suggest that a 400 mg once-daily dose could be implemented in accordance with CYP2B6 polymorphism and body weight. However, the use of nevirapine once daily (immediate release; off-label) in the absence of therapeutic drug monitoring is not recommended due to the risk of inadequate exposure to nevirapine in a high proportion of patients. There are different considerations for the extended-release formulation (nevirapine XR) that demonstrate minimal peak-to-trough fluctuations in plasma nevirapine levels.