ABSTRACT
OBJECTIVE: Tenofovir alafenamide (TAF) preferentially loads peripheral blood mononuclear cells (PBMCs), resulting in higher PBMC tenofovir-diphosphate (TFV-DP) vs. tenofovir disoproxil fumarate (TDF). No studies have yet compared TFV-DP in PBMC from lower than daily dosing between prodrugs, which has potential implications for event-driven preexposure prophylaxis and pharmacologic forgiveness. DESIGN: Two separate randomized, directly observed therapy (DOT) crossover studies (DOT-DBS and TAF-DBS) were conducted to mimic low, medium and high adherence. METHODS: HIV-negative adults were randomized to two 12-week DOT regimens of 33, 67 or 100% of daily dosing with emtricitabine (F)/TAF 200âmg/25âmg (TAF-DBS) or F/TDF 200âmg/300âmg (DOT-DBS), separated by a 12-week washout. PBMC steady-state concentrations (Css) of TFV-DP and FTC-TP were estimated using nonlinear mixed models and compared between F/TAF and F/TDF. RESULTS: Thirty-five participants contributed to 33% (nâ=â23), 67% (nâ=â23) and 100% (nâ=â23) of daily F/TAF regimens. Forty-four contributed to 33% (nâ=â15), 67% (nâ=â16) and 100% (nâ=â32) of daily F/TDF regimens. PBMC TFV-DP Css were 7.3 [95% confidence interval (95% CI): 6.4-8.2], 7.1 (5.9-8.2) and 6.7- (4.4-8.9) fold higher (Pâ<â0.0001) following F/TAF vs. F/TDF; 593 vs. 81.7, 407 vs. 57.4, and 215 vs. 32.3âfmol/106 cells, respectively. TFV-DP was 2.6 (2.1-3.1) fold higher with 33% F/TAF vs. 100% F/TDF. Estimated half-lives (95% CI) of TFV-DP in PBMC were 2.9 (1.5-5.5) days for F/TAF and 2.1 (1.5-2.9) days for F/TDF. FTC-TP was similar in both studies (Pâ=â0.119). CONCLUSION: F/TAF produced 6.7 to 7.3-fold higher TFV-DP in PBMC vs. F/TDF across adherence levels, supporting increased potency and pharmacologic forgiveness with F/TAF in the PBMC compartment.