Abstract
OBJECTIVE: To measure concentrations of tenofovir diphosphate (TFV-DP) in dried blood spots (DBS) among individuals taking tenofovir disoproxil fumarate plus emtricitabine (TDF/FTC) or tenofovir alafenamide plus emtricitabine (TAF/FTC) who were scheduled to undergo or had already undergone bariatric surgery. METHODS: We enrolled pre-exposure prophylaxis (PrEP) users attending clinics in Toronto or Ottawa who were undergoing or had undergone bariatric surgery. After participants completed a minimum of 7 days of consecutive PrEP dosing, we collected DBS samples immediately before they administered their next daily dose of PrEP. Participants who had already undergone bariatric surgery before enrolment provided a single sample at baseline only. One participant undergoing planned bariatric surgery provided samples preoperatively and on postoperative days 7, 28 and 84. TFV-DP was measured by liquid chromatography tandem mass spectrometry. We compared results against the population range TFV-DP at varying degrees of adherence and stratified by chronology of bariatric surgery, type of bariatric surgery and PrEP regimen. RESULTS: Of seven eligible participants, all were gay, cis-gender men. Median age was 48 years (Q1-Q3: 44-51). Six participants underwent bariatric surgery before enrolment: four Roux-en-Y gastric bypass (RYGB) and two sleeve gastrectomy (SG). Four were taking TDF/FTC and two were taking TAF/FTC. All had therapeutic TFV-DP concentrations, except for one TDF/FTC participant who underwent SG. One participant taking TAF/FTC enrolled before receiving RYGB and displayed a slight decrease in TFV-DP over time, although all concentrations remained in the therapeutic range. CONCLUSIONS: Tenofovir diphosphate concentrations were at or near therapeutic values in this small sample of men using oral PrEP who underwent RYGB or SG.