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

Abstract

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.

FIG. 1.

Research participant disposition

FIG. 2.

Study sampling schema. Study phases are indicated across study days from 0 to 49 as planned: Accumulation (day 0–28), Steady-State (day 28–35), and Decay (day 35–49). Up pointing gray arrows indicate all sampling is predose except for terminal day 49 sampling, which occurs 2 weeks after the last dose (day 35). Pharmacokinetic (PK) sampling of blood [serum, peripheral blood mononuclear cells (PBMCs), CD4⁺ cells)] occurs similarly for all subjects except for the presecond dose sample that occurs uniquely for more than weekly frequency regimens (light gray arrows) on day 2 (daily regimen) and day 3 (twice weekly regimens). Tissue-fluid cohort sampling is indicated by black arrows (days 35 and 49 only).

FIG. 3.

(A) Tenofovir analyte predose median (IQR) concentration vs. time relationships for all dosing regimens: one tablet weekly, red triangle; one tablet, two times per week, green square; two tablets twice weekly, blue diamond; one tablet daily, gold circle. (B) Emtricitabine moiety predose median (IQR) concentration vs. time relationships for all dosing regimens: one tablet weekly, red triangle; one tablet, two times per week, green square; two tablets twice weekly, blue diamond; one tablet daily, gold circle.

FIG. 4.

Receiver operating characteristic (ROC) curves for plasma tenofovir (TFV) (left) and PBMC TFV-DP (right). The legend for each figure indicates the dose frequency ranging from one to seven doses per week and the associated area under the curve (AUC) for the ROC curve.