A study presented at last month’s HIV Research for Prevention conference (HIVR4P) in Madrid shows that transgender women who are taking feminising hormones and also taking pre-exposure prophylaxis (PrEP) have levels of the PrEP drugs tenofovir and emtricitabine in their blood that are about 25% lower than those in cisgender men, and levels in rectal tissue cells about 40% lower. Tenofovir levels in rectal tissue were 44% lower.

However the study also confirmed that the interaction between hormones and PrEP did not appear to go the other way; blood levels of estradiol, the one hormone all of the transgender women took in one form or another, do not appear to be affected by PrEP.

The study compared PrEP drug levels in eight transgender women and eight cisgender men. The transgender women were already taking gender-affirming hormone therapy, but no-one was already taking PrEP. All participants were observed taking PrEP each day for eight days (directly observed therapy). The researchers compared PrEP levels between the trans women and cis men in blood, in T-cells and in rectal tissue cells.

Craig Hendrix of Johns Hopkins University said that the differences seen were roughly equivalent to the difference one would expect between someone taking four doses of PrEP a week and someone taking all seven.

The findings add to a Thai study presented at the Amsterdam International AIDS Conference in July, which also found no difference in hormone levels. The Thai study found a smaller (17%) reduction in tenofovir drug levels, whose significance at the time was not clear. Read more via AIDSmap