Assessment of Drug-drug Interactions Between Feminizing Hormone Therapy and Emtricitabine/Tenofovir Alafenamide Concomitantly for Pre-exposure Prophylaxis Among Transgender Women

Inclusion Criteria: 1. Thai nationality 2. Age 18-40 years old 3. Transgender women 4. HIV-negative 5. Body mass index 18.5-24.9 kg/m2 6. Calculated creatinine clearance (CrCl) ≥60 mL/min, as estimated by the Cockcroft-Gault equation 7. Alanine aminotransferase (ALT) ≤2.5 x ULN 8. Signed the informed consent form Exclusion Criteria: 1. Known history of allergy to hormonal component to be used in the study 2. Male-to-female transgender who underwent orchiectomy 3. Use of pre-exposure prophylaxis or post-exposure prophylaxis in the past 30 days 4. Use of injectable FHT in the past 3 months 5. Evidence of current hepatitis B virus infection (HBV) - i.e. hepatitis B surface antigen (HBsAg) positive 6. Evidence of current hepatitis C virus infection (HCV) - i.e. HCV antibody positive 7. Current use of any of the following: * Anticonvulsants: carbamazepine, felbamate, oxcarbazepine, phenytoin, phenobarbital, primidone or topiramate * Herbs: gingko biloba, St John's wort or milk thistle * Anti-infective agents: azole antifungals, macrolides, griseofulvin, protease inhibitors, rifampicin or rifabutin 8. Participant-reported active rectal infection requiring treatment 9. History of gastrointestinal tract surgery that alter gastrointestinal tract and/or drug absorption 10. Alcohol or drug use that, in the opinion of the investigator, would interfere with completion of study procedures