Plasma and intracellular ribavirin concentrations are not significantly altered by abacavir in hepatitis C virus-infected patients

OBJECTIVES

The objective of this study was to evaluate the effects of abacavir on intracellular ribavirin triphosphate and plasma ribavirin trough concentrations.

METHODS

Hepatitis C virus-infected subjects who had been cured or failed prior treatment were randomized to 8 weeks of ribavirin alone (N = 14; weight-based dosing) or weight-based ribavirin + abacavir (N = 14; 300 mg orally every 12 h). Ribavirin trough concentrations were measured on days 14, 28, 42 and 56; PBMCs for ribavirin triphosphate determination were sampled on days 28 and 56, pre-dose and at 6 and 12 h post-dose. ClinicalTrials.gov: NCT01052701.

RESULTS

Twenty-six subjects completed the study (24 males, 17 Caucasians, median age 52 years); 2 were excluded for missed pharmacokinetic visits. Fourteen subjects received ribavirin + abacavir and 12 received ribavirin alone. Mean ± SD plasma ribavirin trough concentrations (μg/mL) on days 14, 28, 42 and 56, respectively, were not significantly different with coadministration of abacavir (1.54 ± 0.60, 1.93 ± 0.54, 2.14 ± 0.73 and 2.54 ± 1.05) compared with ribavirin alone (1.48 ± 0.32, 2.08 ± 0.41, 2.32 ± 0.47 and 2.60 ± 0.62) (P > 0.40). Mean ribavirin triphosphate intracellular concentrations (pmol/10(6) cells) on days 28 and 56, respectively, did not differ statistically between abacavir users (11.98 ± 9.86 and 15.87 ± 12.52) and non-users (15.91 ± 15.58 and 15.93 ± 12.69) (P > 0.4). Adverse events were mild or moderate, except for three grade 3 occurrences of transaminitis, cholecystitis and low absolute neutrophil count that resolved and were judged not attributable to study medications.

CONCLUSIONS

Abacavir did not significantly alter ribavirin or ribavirin triphosphate concentrations.

Dose Frequency Ranging Pharmacokinetic Study of Tenofovir-Emtricitabine After Directly Observed Dosing in Healthy Volunteers to Establish Adherence Benchmarks (HPTN 066)

Oral preexposure prophylaxis (PrEP) trials report disparate efficacy attributed to variable adherence. HPTN 066 was conducted to establish objective, quantitative benchmarks for discrete, regular levels of adherence using directly observed dosing of tenofovir (TFV) disoproxil fumarate (TDF)/emtricitabine (FTC). Healthy, HIV-uninfected men and women were randomized to one of four oral regimens of fixed-dose TDF 300 mg/FTC 200 mg tablet for 5 weeks with all doses observed: one tablet weekly (one/week), one tablet twice weekly (two/week), two tablets twice weekly (four/week), or one tablet daily (seven/week). Trough serum TFV and FTC, peripheral blood mononuclear cell (PBMC), and CD4(+) TFV-diphosphate (TFV-DP) and FTC-triphosphate (FTC-TP) concentrations were determined throughout dosing and 2 weeks after the last dose. Rectosigmoidal, semen, and cervicovaginal samples were collected for drug assessment at end of dosing and 2 weeks later in a subset of participants. The 49 enrolled participants tolerated the regimens well. All regimens achieved steady-state concentrations by the second dose for serum TFV/FTC and by 7 days for PBMC TFV-DP/FTC-TP. Steady-state median TFV-DP predose concentrations demonstrated dose proportionality: one/week 1.6 fmol/10(6) PBMCs, two/week 9.1, four/week 18.8, seven/week, 36.3. Further, TFV-DP was consistently quantifiable 2 weeks after the last dose for the ≥4/week regimens. Adherence benchmarks were identified using receiver operating characteristic curves, which had areas under the curve ≥0.93 for all analytes in serum and PBMCs. Intersubject and intrasubject coefficients of variation (%CV) ranged from 33% to 63% and 14% to 34%, respectively, for all analytes in serum and PBMCs. Steady-state PBMC TFV-DP was established earlier and at lower concentrations than predicted and was the only analyte demonstrating predose concentration dose proportionality. Steady-state daily dosing serum TFV and PBMC TFV-DP was consistent with highly effective PrEP clinical trials. HPTN 066 provides adherence benchmarks for oral TFV/FTC regimens to assist interpreting study outcomes.

Phase 1 clinical trials of DAS181, an inhaled sialidase, in healthy adults

DAS181, (study drug, Fludase®) was developed for treatment of influenza and parainfluenza infections. Delivered by inhalation, DAS181 cleaves sialic acid receptors from respiratory epithelial cells. Treatment of influenza for three days with DAS181 reduced viral shedding. To increase deposition in the upper airways and decrease systemic absorption, the particle size was increased to 10μm. We conducted two Phase I trials with three cohorts, randomized 2:1, active drug to placebo. The initial cohort got a single 20mg dose of DAS181, or placebo; the second, 20mg DAS181 or placebo for 10days, and the third got 20mg of DAS181 or placebo for 3days. Formulations differed slightly in their excipients. Subjects in the 1- and 3-day cohorts completed dosing without serious adverse events. Two subjects in the 10-day cohort stopped at Day 9 after developing respiratory and systemic symptoms, and a third experienced a decrease in FEV1 (Forced Expiratory Volume in 1s) after the 9th dose and a further decline after the 10th dose. Plasma DAS181, in the 10-day cohort, peaked and began falling before the last dose. Antibodies, predominately IgG with neutralizing activity, were detected in 15/18 subjects by Day 30. The highest IgG concentrations were in the 10-day cohort. The respiratory adverse events occurring after seven days and rapid drug clearance during continued dosing are consistent with the induction of DAS181 antibodies. This could preclude use of this medication for longer than seven days or for repeated courses. (These studies have been registered at ClinicalTrials.gov under registration Nos. NCT 00527865 and NCT 01651494.).

Effect of low-dose ritonavir on the pharmacokinetics of the CXCR4 antagonist AMD070 in healthy volunteers

AMD070, a CXCR4 antagonist, has demonstrated antiretroviral activity in human immunodeficiency virus-infected patients. Since AMD070 is a substrate of cytochrome P450 3A4 and P-glycoprotein, both of which may be affected by ritonavir, we tested for a ritonavir effect on AMD070 pharmacokinetics. Subjects were given a single 200-mg dose of AMD070 on days 1, 3, and 17. Ritonavir (100 mg every 12 h) was dosed from day 3 to day 18. Blood samples to test for AMD070 concentrations were collected over 48 h after each administration of AMD070. Twenty-three male subjects were recruited. Among them, 21 completed the study, and 2 were discontinued for reasons other than safety. All adverse events were grade 2 or lower. AMD070 alone had the following pharmacokinetic features, given as medians (ranges): 3 h (0.5 to 4 h) for the time to peak blood concentration, 256 ng/ml (41 to 845 ng/ml) for the peak concentration (C(max)), 934 h x ng/ml (313 to 2,127 h x ng/ml) for the area under the concentration-time curve from 0 h to infinity (AUC(0-infinity)), 214 liters/h (94 to 639 liters/h) for apparent body clearance, and 4,201 liters (1,996 to 9,991 liters) for the apparent volume of distribution based on the terminal phase. The initial doses of ritonavir increased the C(max) of AMD070 [geometric mean (90% confidence interval)] by 39% (3 to 89%) and the AUC(0-infinity) by 60% (29 to 100%). After 14 days of ritonavir dosing, the pharmacokinetic changes in AMD070 persisted. The plasma pharmacokinetics of ritonavir were consistent with previous reports. It is concluded that AMD070 concentrations were increased with concomitant ritonavir dosing for 14 days in healthy volunteers.

Amprenavir and Lopinavir Pharmacokinetics following Coadministration of Amprenavir or Fosamprenavir with Lopinavir/Ritonavir, with or without Efavirenz

Background

Amprenavir (APV), fosamprenavir (FPV), lopinavir (LPV), ritonavir (RTV) and efavirenz (EFV) are to varying degrees substrates, inducers and inhibitors of CYP3A4. Coadministration of these drugs might result in complex pharmacokinetic drug-drug interactions.

Methods

Two prospective, open-label, non-randomized studies evaluated APV and LPV steady-state pharmacokinetics in HIV-infected patients on APV 750 mg twice daily + LPV/RTV 533/133 mg twice daily with EFV ( n=7) or without EFV ( n=12) + background nucleosides (Study 1) and after switching FPV 1,400 mg twice daily for APV ( n=10) (Study 2).

Results

In Study 1 EFV and non-EFV groups did not differ in APV minimum plasma concentration (Cmin; 1.10 versus 1.06μg/ml, P=0.89), area under the concentration-time curve (AUC; 17.46 versus 24.34μg•h/ml, P=0.22) or maximum concentration (Cmax; 2.61 versus 4.33 μg/ml, P=0.08); for LPV there was no difference in Cmin (median: 3.66 versus 6.18μg/ml, P=0.20), AUC (81.84 versus 93.75 μg•h/ml, P=0.37) or Cmax (10.36 versus 10.93 μg/ml, P=0.61). In Study 2, after switching from APV to FPV, APV Cmin increased by 58% (0.83 versus 1.30 μg/ml, P=0.0001), AUC by 76% (19.41 versus 34.24 μg•h/ml, P=0.0001), and Cmax by 75% (3.50 versus 6.14, P=0.001). Compared with historical controls, LPV and RTV pharmacokinetics were not changed. All treatment regimens were well tolerated. Seven of eight completers (88%) maintained HIV-1 RNA <400 copies/ml 12 weeks after the switch (1 lost to follow up).

Conclusions

EFV did not appear to significantly alter APV and LPV pharmacokinetic parameters in HIV-infected patients taking APV 750 mg twice daily + LPV 533/133 mg twice daily. Switching FPV 1,400 mg twice daily for APV 750 mg twice daily resulted in an increase in APV Cmin, AUC, and Cmax without changing LPV or RTV pharmacokinetics or overall tolerability.

Amprenavir and lopinavir pharmacokinetics following coadministration of amprenavir or fosamprenavir with lopinavir/ritonavir, with or without efavirenz

BACKGROUND

Amprenavir (APV), fosamprenavir (FPV), lopinavir (LPV), ritonavir (RTV) and efavirenz (EFV) are to varying degrees substrates, inducers and inhibitors of CYP3A4. Coadministration of these drugs might result in complex pharmacokinetic drug-drug interactions.

METHODS

Two prospective, open-label, non-randomized studies evaluated APV and LPV steady-state pharmacokinetics in HIV-infected patients on APV 750 mg twice daily + LPV/RTV 533/133 mg twice daily with EFV (n=7) or without EFV (n=12) + background nucleosides (Study 1) and after switching FPV 1,400 mg twice daily for APV (n=10) (Study 2).

RESULTS

In Study 1 EFV and non-EFV groups did not differ in APV minimum plasma concentration (Cmin; 1.10 versus 1.06 microg/ml, P = 0.89), area under the concentration-time curve (AUC; 17.46 versus 24.34 microg x h/ml, P = 0.22) or maximum concentration (Cmax; 2.61 versus 4.33 microg/ml, P = 0.08); for LPV there was no difference in Cmin, (median: 3.66 versus 6.18 microg/ml, P = 0.20), AUC (81.84 versus 93.75 microg x h/ml, P = 0.37) or Cmax (10.36 versus 10.93 microg/ml, P = 0.61). In Study 2, after switching from APV to FPV, APV Cmin increased by 58% (0.83 versus 1.30 microg/ml, P = 0.0001), AUC by 76% (19.41 versus 34.24 micorg x h/ml, P = 0.0001), and Cmax by 75% (3.50 versus 6.14, P = 0.001). Compared with historical controls, LPV and RTV pharmacokinetics were not changed. All treatment regimens were well tolerated. Seven of eight completers (88%) maintained HIV-1 RNA <400 copies/ml 12 weeks after the switch (1 lost to follow up).

CONCLUSIONS

EFV did not appear to significantly alter APV and LPV pharmacokinetic parameters in HIV-infected patients taking APV 750 mg twice daily + LPV 533/133 mg twice daily. Switching FPV 1400 mg twice daily for APV 750 mg twice daily resulted in an increase in APV Cmin, AUC, and Cmax without changing LPV or RTV pharmacokinetics or overall tolerability.