Intracellular Tenofovir-Diphosphate and Emtricitabine-Triphosphate in Dried Blood Spots following Directly Observed Therapy

Abstract

Studies of daily emtricitabine-tenofovir disoproxil fumarate (FTC-TDF) for HIV preexposure prophylaxis (PrEP) in men who have sex with men (MSM) modeled intracellular tenofovir-diphosphate (TFV-DP) in dried blood spots (DBS) to assess adherence and corresponding PrEP outcomes. We conducted a prospective, randomized, crossover pharmacokinetic study of TFV-DP in DBS during 33%, 67%, or 100% of daily dosing under directly observed therapy (DOT). Participants were assigned to two 12-week dosing regimens, separated by a 12-week washout. Forty-eight adults (25 women) from Denver and San Francisco were included. TFV-DP exhibited a median half-life of 17 days, reaching steady state in 8 weeks. TFV-DP was dose proportional with mean (SD) steady-state concentrations of 530 (159), 997 (267), and 1,605 (405) fmol/punch for the 33%, 67%, and 100% arms, respectively. Prior work in MSM demonstrated clinically meaningful TFV-DP thresholds of 350, 700, and 1,250 fmol/punch, which were estimated 25th percentiles for 2, 4, and 7 doses/week. In the present study, corresponding TFV-DP was within 3% of the prior estimates, and subgroups by site, race, and sex were within 14% of prior estimates, although males had 17.6% (95% confidence intervals [CIs], 6.5, 27.4%) lower TFV-DP than females. The thresholds of 350, 700, and 1,250 fmol/punch were achieved by 75% of men taking ≥1.2, 3.2, and 6 doses/week and 75% of women taking ≥0.6, 2.0, and 5.3 doses/week, indicating that lower dosing reached these thresholds for both sexes. In conclusion, TFV-DP arising from DOT was similar to previous estimates and is useful for interpreting PrEP adherence and study outcomes. (This study has been registered at ClinicalTrials.gov under identifier NCT02022657.).

Keywords: HIV; adherence; intracellular; nucleoside analog; pharmacokinetics; preexposure prophylaxis.

FIG 1

Observed TFV-DP from week 12 or 36 (y axis) according to intermittent (I) or holiday (H) study arm (x axis). The limits of the box represent the 1st and 3rd data quartiles (Q1 and Q3), the interior horizontal line denotes the median, and the asterisk represents the mean. The whiskers extend to the most extreme point within a value of 1.5 × (Q3 − Q1) of the corresponding hinge, beyond which outliers are represented by a circle.

FIG 2

TFV-DP (y axis) by actual day of therapy (x axis) for 100% (blue), 67% (green), and 33% (red) dosing regimens. Intermittent and holiday are combined, and both dosing periods are included from days 0 to ∼84, followed by the washout between dosing periods (right of dashed line). Open symbols depict observed concentrations, and closed symbols are fitted concentrations. The inset shows the modeled average for each regimen overlaid on the observed data during dosing periods.

FIG 3

Natural log TFV-DP from DBS derived from fingerstick (y axis) versus TFV-DP from a paired DBS collected from venipuncture (samples were collected at the same time). The solid line is the line of agreement. The interclass correlation was 0.89.

FIG 4

Estimated 25th, 50th, and 75th percentiles for the percentage of doses taken (y axis) for a given TFV-DP concentration in fmol/punch (x axis). Open symbols and dashed lines represent 300, 700, and 1,250 fmol/punch, values used in previous clinical studies. Estimates for males are on the left and females on the right.

FIG 5

DBS were assayed for quantitation or detection of FTC-TP (numbers of samples assayed are listed above the bars). The percentage of FTC-TP samples (y axis) either quantifiable (hatched pattern) or detectable (checkered pattern) per study arm (x axis) is shown.

FIG 6

HIV-negative volunteers were randomized to one of six 12-week sequences of two directly observed (DOT) dosing regimens (left rectangle and then right rectangle) separated by a 12-week washout (open space). Thirty-three and 67% dosing were split into intermittent and holiday patterns (not shown). The timeline and collection of DBS, DBS by fingerstick (DBS-FS), and hair are indicated along the bottom.