Sex Hormone Therapy and Tenofovir Diphosphate Concentration in Dried Blood Spots: Primary Results of the iBrEATHe Study

BACKGROUND Pilot studies showed lower tenofovir plasma concentrations during PrEP use among transgender women (TGW) using feminizing hormones compared with cisgender men (CGM). Tenofovir diphosphate (TFV-DP) concentrations in TGW and transgender men (TGM) using gender affirming hormones and on directly observed dosing of PrEP have not been studied. METHODS TGM and TGW on at least 6 months of stable sex hormone therapy containing testosterone or estradiol (respectively) were enrolled in a 4-week study of directly observed dosing of daily oral co-formulated emtricitabine and tenofovir disoproxil fumarate (FTC/TDF). TFV-DP in dried blood spots and sex hormones in serum were measured at weekly intervals. TFV-DP was compared with 2 and 4 week samples from DOT-DBS (NCT02022657). RESULTS From May 2017 to June 2018, 24 TGM and 24 TGW were enrolled; one TGM withdrew prior to 4 weeks of PrEP. Ethnicity (non-exclusive) was 27 (57%) white, 10 (21%) black, and 15 (32%) latinx. The median age was 31 (IQR 28 to 40). Of TGW, 9 (38%) took spironolactone in addition to estradiol. Testosterone (total and free) and estradiol concentrations were comparable before and after 4 weeks of PrEP use in TGM and TGW respectively. Historical controls comprised of 17 cisgender women (CGW) and 15 CGM. TFV-DP concentrations at week 4 were comparable between TGW and TGM (mean difference -6%; 95% CI -21% to 12%; P=0.47), comparable between TGW and CGM (mean difference -12%; 95% CI -27% to 7%; P=0.21) and were lower among TGM compared with CGW (mean difference -23%; 95% CI -36% to -7%; P=0.007). All persons in all groups were projected to reach the TFV-DP threshold that has been associated with high protection from HIV. There were no associations between serum estradiol or free testosterone concentrations and TFV-DP. CONCLUSION CGM, TGM, and TGW had comparable TFV-DP concentrations in DBS after 4 weeks of directly observed daily FTC/TDF PrEP use. Serum hormone concentrations were not affected by FTC/TDF PrEP use.