Dose response for starting and stopping HIV preexposure prophylaxis for men who have sex with men.

BACKGROUND: This study estimated the number of daily tenofovir disoproxil fumarate/emtricitabine (TDF/FTC) doses required to achieve and maintain (after discontinuation) intracellular drug concentrations that protect against human immunodeficiency virus (HIV) infection for men who have sex with men (MSM). METHODS: Tenofovir diphosphate (TFV-DP) concentrations in peripheral blood mononuclear cells (PBMCs) and rectal mononuclear cells from an intensive pharmacokinetic study ("Cell-PrEP" [preexposure prophylaxis]) of 30 days of daily TDF/FTC followed by 30 days off drug were evaluated. A regression formula for HIV risk reduction derived from PBMCs collected in the preexposure prophylaxis initiative study was used to calculate inferred risk reduction. The time required to reach steady state for TFV-DP in rectal mononuclear cells was also determined. RESULTS: Twenty-one HIV-uninfected adults participated in Cell-PrEP. The inferred HIV risk reduction, based on PBMC TFV-DP concentration, reached 99% (95% confidence interval [CI], 69%-100%) after 5 daily doses, and remained >90% for 7 days after stopping drug from steady-state conditions. The proportion of participants reaching the 90% effective concentration (EC90) was 77% after 5 doses and 89% after 7 doses. The percentage of steady state for natural log [TFV-DP] in rectal mononuclear cells was 88% (95% CI, 66%-94%) after 5 doses and 94% (95% CI, 78%-98%) after 7 doses. CONCLUSIONS: High PrEP activity for MSM was achieved by approximately 1 week of daily dosing. Although effective intracellular drug concentrations persist for several days after stopping PrEP, a reasonable recommendation is to continue PrEP dosing for 4 weeks after the last potential HIV exposure, similar to recommendations for postexposure prophylaxis.

Impact of the CYP2C8 *3 polymorphism on the drug-drug interaction between gemfibrozil and pioglitazone.

AIM: The objective of this study was to determine the extent to which the CYP2C8*3 allele influences pharmacokinetic variability in the drug-drug interaction between gemfibrozil (CYP2C8 inhibitor) and pioglitazone (CYP2C8 substrate). METHODS: In this randomized, two phase crossover study, 30 healthy Caucasian subjects were enrolled based on CYP2C8*3 genotype (n = 15, CYP2C8*1/*1; n = 15, CYP2C8*3 carriers). Subjects received a single 15 mg dose of pioglitazone or gemfibrozil 600 mg every 12 h for 4 days with a single 15 mg dose of pioglitazone administered on the morning of day 3. A 48 h pharmacokinetic study followed each pioglitazone dose and the study phases were separated by a 14 day washout period. RESULTS: Gemfibrozil significantly increased mean pioglitazone AUC(0,∞) by 4.3-fold (P < 0.001) and there was interindividual variability in the magnitude of this interaction (range, 1.8- to 12.1-fold). When pioglitazone was administered alone, the mean AUC(0,∞) was 29.7% lower (P = 0.01) in CYP2C8*3 carriers compared with CYP2C8*1 homozygotes. The relative change in pioglitazone plasma exposure following gemfibrozil administration was significantly influenced by CYP2C8 genotype. Specifically, CYP2C8*3 carriers had a 5.2-fold mean increase in pioglitazone AUC(0,∞) compared with a 3.3-fold mean increase in CYP2C8*1 homozygotes (P = 0.02). CONCLUSION: CYP2C8*3 is associated with decreased pioglitazone plasma exposure in vivo and significantly influences the pharmacokinetic magnitude of the gemfibrozil-pioglitazone drug-drug interaction. Additional studies are needed to evaluate the impact of CYP2C8 genetics on the pharmacokinetics of other CYP2C8-mediated drug-drug interactions.

Effect of ABCB1 polymorphisms and atorvastatin on sitagliptin pharmacokinetics in healthy volunteers.

OBJECTIVES: The objectives of this study were to determine if ABCB1 polymorphisms are associated with interindividual variability in sitagliptin pharmacokinetics and if atorvastatin alters the pharmacokinetic disposition of sitagliptin in healthy volunteers. METHODS: In this open-label, randomized, two-phase crossover study, healthy volunteers were prospectively stratified according to ABCB1 1236/2677/3435 diplotype (n = 9, CGC/CGC; n = 10, CGC/TTT; n = 10, TTT/TTT). In one phase, participants received a single 100 mg dose of sitagliptin; in the other phase, participants received 40 mg of atorvastatin for 5 days, with a single 100 mg dose of sitagliptin administered on day 5. A 24-h pharmacokinetic study followed each sitagliptin dose, and the study phases were separated by a 14-day washout period. RESULTS: Sitagliptin pharmacokinetic parameters did not differ significantly between ABCB1 CGC/CGC, CGC/TTT, and TTT/TTT diplotype groups during the monotherapy phase. Atorvastatin administration did not significantly affect sitagliptin pharmacokinetics, with geometric mean ratios (90 % confidence intervals) for sitagliptin maximum plasma concentration, plasma concentration-time curve from zero to infinity, renal clearance, and fraction of sitagliptin excreted unchanged in the urine of 0.93 (0.86-1.01), 0.96 (0.91-1.01), 1.02 (0.93-1.12), and 0.98 (0.90-1.06), respectively. CONCLUSIONS: ABCB1 CGC/CGC, CGC/TTT, and TTT/TTT diplotypes did not influence sitagliptin pharmacokinetics in healthy volunteers. Furthermore, atorvastatin had no effect on the pharmacokinetics of sitagliptin in the setting of ABCB1 CGC/CGC, CGC/TTT, and TTT/TTT diplotypes.

Effect of antacids on the pharmacokinetics of raltegravir in human immunodeficiency virus-seronegative volunteers.

Raltegravir's divalent metal ion chelating motif may predispose the drug to interactions with divalent cations. We determined whether a divalent cation-containing antacid interacted with raltegravir. Twelve HIV-1-seronegative subjects were enrolled in this randomized, prospective, crossover study of single-dose raltegravir (400 mg) with and without an antacid. Subjects underwent two intensive pharmacokinetic visits in the fasted state separated by a 5- to 12-day washout period. With simultaneous antacid administration, time to peak raltegravir concentration occurred 2 h sooner (P = 0.002) and there was a 67% lower raltegravir concentration at 12 h postdose (P < 0.0001) than with administration of raltegravir alone. The raltegravir area under the-concentration-time curve from 0 to 12 h and maximum concentration were unchanged with the addition of an antacid. Studies are needed to determine the clinical relevance of this interaction, whether it remains after multiple dosing to steady state, whether it is mitigated by temporal separation, and whether raltegravir interacts with divalent cation-containing vitamins, supplements, or foods.

Intracellular Tenofovir and Emtricitabine Anabolites in Genital, Rectal, and Blood Compartments from First Dose to Steady State.

The pharmacokinetics (PK) of tenofovir-diphosphate (TFV-DP) and emtricitabine-triphosphate (FTC-TP), the active anabolites of tenofovir disoproxil fumarate (TDF), and emtricitabine (FTC) in blood, genital, and rectal compartments was determined in HIV-positive and seronegative adults who undertook a 60-day intensive PK study of daily TDF/FTC (plus efavirenz in HIV positives). Lymphocyte cell sorting, genital, and rectal sampling occurred once per subject, at staggered visits. Among 19 HIV-positive (3 female) and 21 seronegative (10 female) adults, TFV-DP in peripheral blood mononuclear cells (PBMC) accumulated 8.6-fold [95% confidence interval (CI): 7.2-10] from first-dose to steady-state concentration (Css) versus 1.7-fold (95% CI: 1.5-1.9) for FTC-TP. Css was reached in ∼11 and 3 days, respectively. Css values were similar between HIV-negative and HIV-positive individuals. Css TFV-DP in rectal mononuclear cells (1,450 fmol/106 cells, 898-2,340) was achieved in 5 days and was >10 times higher than PBMC (95 fmol/106 cells, 85-106), seminal cells (22 fmol/106 cells, 6-79), and cervical cells (111 fmol/106 cells, 64-194). FTC-TP Css was highest in PBMC (5.7 pmol/106 cells, 5.2-6.1) and cervical cells (7 pmol/106 cells, 2-19) versus rectal (0.8 pmol/106 cells, 0.6-1.1) and seminal cells (0.3 pmol/106 cells, 0.2-0.5). Genital drug concentrations on days 1-7 overlapped with estimated Css, but accumulation characteristics were based on limited data. TFV-DP and FTC-TP in cell sorted samples were highest and achieved most rapidly in CD14+ compared with CD4+, CD8+, and CD19+ cells. Together, these findings demonstrate cell-type and tissue-dependent cellular pharmacology, preferential accumulation of TFV-DP in rectal mononuclear cells, and rapid distribution into rectal and genital compartments.

Pharmacokinetic interaction between boceprevir and etravirine in HIV/HCV seronegative volunteers.

OBJECTIVE: The primary aim of this study was to determine the bioequivalence of boceprevir, an HCV protease inhibitor and etravirine, an HIV non-nucleoside reverse transcriptase inhibitor; area under the concentration time curve (AUC(0,τ)); maximum concentration (C(max)); and trough concentration (C(8) or C(min)) when administered in combination versus alone. DESIGN: Open-label crossover study in healthy volunteers. METHODS: Boceprevir, etravirine, and the combination were administered for 11-14 days with intensive sampling between days 11 and 14 of each sequence. Boceprevir and etravirine were quantified using validated liquid chromatography coupled with tandem mass spectrometry and high-performance liquid chromatography/ultraviolet assays, respectively and pharmacokinetics determined using noncompartmental methods. Geometric mean ratios (GMRs) and 90% confidence interval (CI) for the combination versus each drug alone were evaluated using 2 one-sided t tests. The hypothesis of equivalence was rejected if 90% GMR CI was not contained in the interval (0.8-1.25). RESULTS: Twenty subjects completed study. GMRs (90% CI) for etravirine AUC(o,τ), C(max), and C(min) were 0.77 (0.66 to 0.91), 0.76 (0.68 to 0.85), and 0.71 (0.54 to 0.95), respectively, in combination versus alone. Boceprevir GMRs (90% CI) for AUC(o,τ), C(max), and C(8) were 1.10 (0.94 to 1.28), 1.10 (0.94 to 1.29), and 0.88 (0.66 to 1.17), respectively, in combination versus alone. All adverse events (n = 112) were mild or moderate. Six subjects discontinued: 4 due to rash, 1 due to central nervous system effects, and 1 for a presumed viral illness. CONCLUSIONS: Etravirine AUC(o,τ), C(max), and C(min)decreased 23%, 24%, and 29%, respectively, with boceprevir. Boceprevir AUC(0,τ) and C(max) increased 10% and C(8) decreased 12% by etravirine. Additional research is needed to elucidate the mechanism(s) and therapeutic implications of the observed interaction.

Influence of CYP2C8*2 on the pharmacokinetics of pioglitazone in healthy African-American volunteers.

STUDY OBJECTIVES: To determine the influence of the Cytochrome P450 (CYP) 2C8*2 polymorphism on pioglitazone pharmacokinetics in healthy African-American volunteers. DESIGN: Prospective, open-label, single-dose pharmacokinetic study. SETTING: University of Colorado Hospital Clinical and Translational Research Center. PARTICIPANTS: Healthy African-American volunteers between 21 and 60 years of age were enrolled in the study based on CYP2C8 genotype: CYP2C8*1/*1 (9 participants), CYP2C8*1/*2 (7 participants), and CYP2C8*2/*2 (1 participant). INTERVENTION: Participants received a single 15-mg dose of pioglitazone in the fasted state, followed by a 48-hour pharmacokinetic study. MEASUREMENTS AND MAIN RESULTS: Plasma concentrations of pioglitazone and its M-III (keto) and M-IV (hydroxy) metabolites were compared between participants with the CYP2C8*1/*1 genotype and CYP2C8*2 carriers. Pioglitazone area under the plasma concentration-time curve (AUC)0-∞ and half-life (t1/2 ) did not differ significantly between CYP2C8*1/*1 and CYP2C8*2 carriers (AUC0-∞ 7331 ± 2846 vs 10431 ± 5090 ng*h/ml, p=0.15, t1/2 7.4 ± 2.7 vs 10.5 ± 4.0 h, p=0.07). M-III and M-IV AUC0-48 also did not differ significantly between genotype groups. However, the M-III:pioglitazone AUC0-48 ratio was significantly lower in CYP2C8*2 carriers than CYP2C8*1 homozygotes (0.70 ± 0.15 vs 1.2 ± 0.37, p=0.006). Similarly, CYP2C8*2 carriers had a significantly lower M-III:M-IV AUC0-48 ratio than participants with the CYP2C8*1/*1 genotype (0.82 ± 0.26 vs 1.22 ± 0.26, p=0.006). CONCLUSION: These data suggest that CYP2C8*2 influences pioglitazone pharmacokinetics in vivo, particularly the AUC0-48 ratio of M-III:parent drug, and the AUC0-48 ratio of M-III:M-IV. Larger studies are needed to further investigate the impact of CYP2C8*2 on the pharmacokinetics of CYP2C8 substrates in individuals of African descent.

Influence of SLCO1B1 polymorphisms on the drug-drug interaction between darunavir/ritonavir and pravastatin.

The authors investigated whether SLCO1B1 polymorphisms contribute to variability in pravastatin pharmacokinetics when pravastatin is administered alone versus with darunavir/ritonavir. HIV-negative healthy participants were prospectively enrolled on the basis of SLCO1B1 diplotype: group 1 (*1A/*1A, n = 9); group 2 (*1A/*1B, n = 10; or *1B/*1B, n = 2); and group 3 (*1A/*15, n = 1; *1B/*15, n = 5; or *1B/*17, n = 1). Participants received pravastatin (40 mg) daily on days 1 through 4, washout on days 5 through 11, darunavir/ritonavir (600/100 mg) twice daily on days 12 through 18, with pravastatin 40 mg added back on days 15 through 18. Pharmacokinetic studies were conducted on day 4 (pravastatin alone) and day 18 (pravastatin + darunavir/ritonavir). Pravastatin area under the plasma concentration-time curve (AUC(tau)) was 21% higher during administration with darunavir/ritonavir compared with pravastatin alone; however, this difference was not statistically significant (P = .11). Group 3 variants had 96% higher pravastatin AUC(tau) on day 4 and 113% higher pravastatin AUC(tau) on day 18 compared with group 1. The relative change in pravastatin pharmacokinetics was largest in group 3 but did not differ significantly between diplotype groups. In sum, the influence of SLCO1B1*15 and *17 haplotypes on pravastatin pharmacokinetics was maintained in the presence of darunavir/ritonavir. Because OATP1B1 inhibition would be expected to be greater in carriers of normal or high-functioning SLCO1B1 haplotypes, these findings suggest that darunavir/ritonavir is not a potent inhibitor of OATP1B1-mediated pravastatin transport in vivo.

Drug/Drug interaction between lopinavir/ritonavir and rosuvastatin in healthy volunteers.

OBJECTIVES: This open-label, single-arm, pharmacokinetic (PK) study in HIV-seronegative volunteers evaluated the bioequivalence of rosuvastatin and lopinavir/ritonavir when administered alone and in combination. Tolerability and lipid changes were also assessed. METHODS: Subjects took 20 mg of rosuvastatin alone for 7 days, then lopinavir/ritonavir alone for 10 days, and then the combination for 7 days. Intensive PK sampling was performed on days 7, 17, and 24. RESULTS: Twenty subjects enrolled, and PK data were available for 15 subjects. Geometric mean (+/-SD) rosuvastatin area under the concentration time curve (AUC)[0,tau] and maximum concentration (Cmax) were 47.6 ng.h/mL (+/-15.3) and 4.34 ng/mL (+/-1.8), respectively, when given alone versus 98.8 ng.h/mL (+/-65.5) and 20.2 ng/mL (+/-16.9) when combined with lopinavir/ritonavir (P < 0.0001). The geometric mean ratio was 2.1 (90% confidence interval [CI]: 1.7 to 2.6) for rosuvastatin AUC[0,tau] and 4.7 (90% CI: 3.4 to 6.4) for rosuvastatin Cmax with lopinavir/ritonavir versus rosuvastatin alone (P < 0.0001). There was 1 asymptomatic creatine phosphokinase elevation 17 times the upper limit of normal (ULN) and 1 liver function test elevation between 1.1 and 2.5 times the ULN with the combination. CONCLUSIONS: Rosuvastatin low-density lipoprotein reduction was attenuated with lopinavir/ritonavir. Rosuvastatin AUC and Cmax were unexpectedly increased 2.1- and 4.7-fold in combination with lopinavir/ritonavir. Rosuvastatin and lopinavir/ritonavir should be used with caution until the safety, efficacy, and appropriate dosing of this combination have been demonstrated in larger populations.