SAT391 Supratherapeutic Estrogen Levels in Transgender Women Likely From Sublingual Estradiol

Disclosure: E. Jalal: None. C. Baldwin: None. Transgender medicine is typically managed in the outpatient setting. We report a case where the patient’s hospitalization provided unique insight into hormone management to achieve cis-female range estrogen and testosterone levels in a monitored environment.A 38-year-old transgender woman with HIV (on antiretroviral therapy) complicated by neurocognitive disorder, polysubstance use, mood disorder with previous suicidal ideation, and polytrauma (currently wheelchair bound) was admitted for respiratory failure from MRSA pneumonia. She completed 14 days of antibiotics with resolution of acute medical problems, but ability to secure a safe discharge plan prolonged her hospitalization. Endocrinology was consulted to aid in oral estradiol (E2) management.Prior to admission, patient reported taking 10mg of oral E2 daily. While hospitalized, she was given 6mg E2 daily, but requested resumption of her home dose. Initial total estrogen and testosterone levels were 913 pg/mL (56-213 pg/mL) and 105 ng/dL (264-916 ng/dL), respectively. She denied estrogen pellets, implants, or consumption of additional E2 beyond 6mg daily, nor did she have visitors who provided supplemental hormone; however, she admitted that she does not swallow the E2 pills immediately.Endocrinology initiated intramuscular leuprolide to suppress her total testosterone production to the female range of 0-50 ng/dL, allow for decreased dosing of E2 to maintain female range estrogen levels, and minimize venous thromboembolism (VTE) risk given reduced patient mobility. Her E2 was held for 5 days, with a subsequent total estrogen level of 398 pg/mL (56-213 pg/mL). She was restarted on oral E2 2mg, with total estrogen levels of 238 pg/mL and 517 pg/mL (56-213 pg/mL) at three and six days respectively. Oral E2 was again held for an additional four days, leading to total estrogen level of 119 pg/mL (56-213 pg/mL) and total testosterone of 18 ng/dL (264-916 ng/dL). Her final regimen is now oral E2 1mg daily. She did not develop VTE while hospitalized.Research into the pharmacokinetics of oral versus sublingual E2 is scarce. Differences in absorption explain this patient’s supratherapeutic estrogen level of 913 pg/mL and insufficiently suppressed total testosterone of 105 ng/dL. Sublingual E2 achieves higher peak levels but multi-daily dosing is required to fully suppress testosterone production when compared to its oral counterpart, which corresponds to this patient’s initial laboratory findings. Sublingual E2 also has a lower risk of VTE since it avoids first-pass metabolism. Future research should target alternative routes of estrogen therapy that may potentially be safer than current modalities. Presentation: Saturday, June 17, 2023