Intracellular Tenofovir-Diphosphate and Emtricitabine-Triphosphate in Dried Blood Spots Following Tenofovir Alafenamide: The TAF-DBS Study

Abstract

Background: Tenofovir alafenamide (TAF), in combination with FTC, was recently approved for PrEP in the United States. The objective of this study was to assess the relationship between tenofovir-diphosphate (TFV-DP) and emtricitabine-triphosphate (FTC-TP) in dried blood spots (DBS) with adherence to TAF/FTC. Methods: TAF-DBS was a randomized, crossover clinical study of TFV-DP in DBS, following directly observed dosing of 33%, 67%, or 100% of daily TAF (25 mg)/FTC (200 mg). Healthy volunteers were randomized to 2 different, 12-week dosing regimens, separated by a 12-week washout. DBS were collected weekly. TFV-DP and FTC-TP were extracted from two 7-mm punches and assayed with LC-MS/MS. Results: Thirty-seven participants (17 female, 7 African American, and 6 Hispanic) were included. TFV-DP exhibited a mean half-life of 20.8 days (95% confidence interval: 19.3 to 21.3). The slope for TFV-DP versus dosing arm was 1.14 (90% confidence interval: 1.07 to 1.21). The mean (SD) TFV-DP after 12 weeks was 657 (186), 1451 (501), and 2381 (601) fmol/2 7-mm punches for the 33%, 67%, and 100% arms. The following adherence interpretations are proposed: <450 fmol/punches, <2 doses/wk; 450–949 fmol/punches, 2–3 doses/wk; 950–1799 fmol/punches, 4–6 doses/wk; and ≥1800 fmol/punches, 7 doses/wk. FTC-TP was quantifiable for 1 week after drug cessation in 50%, 92%, and 100% of participants in the 33%, 67%, and 100% arms, respectively. Conclusion: TFV-DP in DBS after TAF/FTC exhibited a long half-life and was linearly associated with dosing, similar to its predecessor tenofovir disoproxil fumarate. FTC-TP was quantifiable for up to 1 week after drug cessation. Together, these moieties provide complementary measures of cumulative adherence and recent dosing for TAF/FTC.

Moderately High Tenofovir Diphosphate in Dried Blood Spots Indicates Drug Resistance in Viremic Persons Living with HIV

“…7,8 Tenofovir diphosphate in RBCs (measured using dried blood spots, DBS) is dose proportional, which makes it an informative measure of cumulative/averaged dosing over the preceding 8 weeks (ie, drug adherence) and exposure to TFV disoproxil fumarate (TDF) and TFV alafenamide. 7–9 Similarly, emtricitabine (FTC) undergoes intracellular phosphorylation in RBCs to emtricitabine triphosphate (FTC-TP), with a half-life of approximately 1.5 days in this matrix, which translates into a measure of recent dosing (ie, within the previous 2-3 days). 10,11 As an adherence assessment, TFV-DP in DBS has previously been shown to be predictive of efficacy to pre-exposure prophylaxis in high-risk men who have sex with men, 12 strongly associated with HIV viral suppression, and predictive of future viremia in PLWH.…”

Lower Urine Tenofovir Concentrations Among Individuals Taking Tenofovir Alafenamide Versus Tenofovir Disoproxil Fumarate: Implications for Point-of-Care Testing

“…Thirty-six TAF-DBS participants [ 10 ] (17 female, 7 black, and 6 Latinx, with a median age of 29 [range, 18–41] years and a median eGFR of 98 [range, 78–137] mL/minute/1.73 m 2 ) each provided 2 urine samples for this analysis (72 urine samples total).…”

“…We leveraged urine specimens from The Cellular Pharmacology of F-TAF in Dried Blood Spots (TAF-DBS), a randomized prospective DOT study performed at the University of Colorado (ClinicalTrials.gov identifier NCT02962739) [ 10 ]. In this study, adults without HIV deemed at low risk for HIV infection were randomized to take TAF 25 mg/FTC 200 mg at either 33%, 67%, or 100% of daily dosing for 12 weeks.…”

Using the adherence‐efficacy relationship of emtricitabine and tenofovir disoproxil fumarate to calculate background HIV incidence: a secondary analysis of a randomized, controlled trial

“…We present an approach using the well-understood relationship between adherence and HIV prevention efficacy with F/TDF gained from experience of prior trials with objective adherence data from TFV-DP in DBS to calculate a counterfactual bHIV in the trial participants. TFV-DP in DBS is a unique adherence assessment given its 2.5-week half-life, so levels represent cumulative adherence in the preceding six to eight weeks [30,31].…”

“…TFV-DP levels were categorized in three adherence categories: <350 fmol/punch (<2 tablets/week), 350 to <700 fmol/punch (2 to 3 tablets/week) and ≥700 fmol/punch (≥4 tablets/week). Methods and benchmarks for F/TAF and F/TDF have been previously described [30,31]. Data were collected between 13 September 2016 and 22 February 2019.…”