Kimberly K Scarsi

Background Feminizing hormone therapy (FHT) is essential to many trans women. Concern about negative drug interactions between FHT and ART can be an ART adherence barrier among trans women with HIV. Objectives In this single-centre, parallel group, cross-sectional pilot study, we measured serum oestradiol concentrations in trans women with HIV taking FHT and unboosted integrase strand transfer inhibitor (INSTI)-based ART versus trans women without HIV taking FHT. Methods We included trans women with and without HIV, aged ≥18 years, taking ≥2 mg/day of oral oestradiol for at least 3 months plus an anti-androgen. Trans women with HIV were on suppressive ART ≥3 months. Serum oestradiol concentrations were measured prior to medication dosing and 2, 4, 6 and 8 h post-dose. Median oestradiol concentrations were compared between groups using Wilcoxon rank-sum tests. Results Participants (n = 8 with HIV, n = 7 without) had a median age of 32 (IQR: 28, 39) years. Among participants, the median oral oestradiol dose was 4 mg (range 2–6 mg). Participants had been taking FHT for a median of 4 years (IQR: 2, 8). Six trans women with HIV were taking bictegravir/emtricitabine/tenofovir alafenamide and two were taking dolutegravir/abacavir/lamivudine. All oestradiol concentrations were not significantly different between groups. Eleven (73%) participants had target oestradiol concentrations in the range 200–735 pmol/L at C4h (75% among women with HIV, 71% among those without HIV). Conclusions Oestradiol concentrations were not statistically different in trans women with HIV compared with those without HIV, suggesting a low probability of clinically relevant drug–drug interactions between FHT and unboosted INSTI-based ART.