648 – Estradiol Concentrations in Trans Women on BIC/FTC/TAF Compared to Those Without HIV

Background

Accessing feminizing hormone therapy (FHT) is essential to many trans women. Concern around drug-drug interactions between FHT and antiretroviral therapy (ART) can be a barrier to acceptance of ART for trans women with HIV. We measured serum estradiol concentrations in trans women with HIV taking FHT and BIC/FTC/TAF versus trans women without HIV taking FHT and no ART.

Methods

This was a single-center, parallel group, clinical study of adult trans women with HIV taking ART and without HIV not taking ART. Participants were taking at least 2 mg/day of oral 17-beta estradiol plus an anti-androgen therapy, with no FHT medication changes for at least 3 months prior to entry. Women with HIV were on suppressive ART for at least 6 months, either taking or switched to BIC/FTC/TAF at entry. At the month 2 visit, blood was collected prior to ART and FHT dosing and then at 1, 2, 3, 4, 6, 8, and 24 hours post-dose. Estradiol concentrations were measured from serum using chemiluminescent microparticle immunoassay (CMIA). Area under the concentration-time curve (AUC) over 24 hours was calculated by noncompartmental methods. Median estradiol maximum concentration (C_max), time to C_max (T_max) and AUC were compared between groups using Wilcoxon rank-sum tests. Data are reported as medians (IQRs).

Results

Participants (n=25) were enrolled from November 2022 to June 2024 and the 10 participants on ART had a median age of 36.5 (30, 45.25) years compared to 29 (27, 37.5) years for the 15 control participants (p=0.173). The median oral estradiol dose was 4 mg (range 2-8 mg) overall and 4 (4, 4) for the ART group and 4 (3, 4) for the control (p=0.232). Anti-androgen therapy included spironolactone (n=12), cyproterone (n=8), orchidectomy (n=4), and hypogonadism (n=1). Estradiol C_max and T_max for the ART group were 357.5 pmol/L(257, 512.25) and 1.5 hours (2, 2.75), respectively and 262 pmol/L (151.5, 312) (p=0.115) and 4 hours (2, 7) (p=0.130) for controls (Figure). AUCs were not different between groups: 5827 mg*h/L (4488, 8352) for the ART group and 4808 mg*h/L (2952, 6281) for controls (p=0.235). Overall, 64% had estradiol C_4h within the target of 200-750 pmol/L[80% among women on ART and 53% among those not on ART (p=0.229)].  

Conclusions

Among trans women on FHT, estradiol concentrations were similar between trans women on BIC/FTC/TAF and controls. This suggests a low probability of clinically relevant drug-drug interactions between FHT and BIC/FTC/TAF.

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