Achieving Physiologic 17-ẞ-Estradiol Levels in Transgender Females on Estradiol Transdermal Patches and Optimal Dosing

Purpose: Gender dysphoria is defined as a significant incongruence between an individual’s experienced gender and the gender assigned at birth, leading to persistent distress. Hormone therapy and gender affirmation surgery improve gender dysphoria by mitigating or completely removing undesirable primary/secondary sexual characteristics which would better align with one’s physical and psychological features. Maintaining cross-sex hormone levels in the physiologic range for the preferred gender is the basis of transgender hormonal therapy. For trans females (MTF), estradiol is most commonly administered orally, and studies have shown this route is often successful in achieving therapeutic hormone levels. However, there is wide individual variability in the dose response to oral estradiol, and approximately 25% of patients will not reach therapeutic goal on maximum oral estradiol. Furthermore, high dose oral estrogen has been associated with increased thrombotic risk, especially in older individuals. The efficacy or optimal dose of adding or switching to the transdermal route is not known. We investigated the efficacy of estradiol transdermal patches and the optimal dose to reach therapeutic goal. Methods: A chart review was conducted of all MTF patients who were treated with estradiol transdermal patches in our transgender clinic from 2006 through 2020. We looked at the success of achieving physiologic serum 17-β-estradiol levels (with and without antiandrogens spironolactone and finasteride) on various doses of estradiol transdermal patches. Target serum level for estradiol >100 pg/mL is recommended (but may be lower in certain clinical circumstances). Results: 371 MTF patients were identified, 41 received an estradiol transdermal patch. Of these 41 patients, 16 of them were placed on a transdermal patch due to failure to achieve target 17-β-estradiol levels on maximal oral therapy. We found that 9 of these 16 patients achieved goal estrogen levels, as well as one patient very near goal. Of the 7 who did not reach goal, only 2 were on patch doses >60 mcg/day. The majority who reached goal serum estradiol levels were taking a dose of 100 mcg/daily. When considering all MTF patients on the highest dose (100 mcg) of transdermal estrogen, 11 of 18 attained goal level, as well as one just under goal. Of the 41 MTF patients taking a transdermal patch, only 6 of them had serum estrogen levels lowered from being at goal on oral therapy. Thirteen patients had their estrogen levels improve to reach goal when placed on patch (4 as add-on therapy). Conclusions: Our study supports the findings that using an estradiol transdermal patch can help MTF patients achieve goal 17-β-estradiol levels. This delivery method can be useful for patients unable to reach goal on oral agents and for patients at higher thrombotic risk. The highest dose patch available is often needed to achieve therapeutic goal.