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

Two full pharmacokinetic (PK) measurements will be performed. Samples collected will include: plasma for estradiol (E2), emtricitabine (FTC), tenofovir (TFV), and tenofovir alafenamide (TAF) measurement; and peripheral blood mononuclear cells (PBMC) for emtricitabine-triphosphate (FTC-TP) and tenofovir-diphosphate (TFV-DP) intracellular quantification.

Inclusion criteria

• Thai nationality
• Age 18-40 years old
• Transgender women
• HIV-negative
• Body mass index 18.5-24.9 kg/m2
• Calculated creatinine clearance (CrCl) ≥60 mL/min, as estimated by the Cockcroft-Gault equation
• Alanine aminotransferase (ALT) ≤2.5 x ULN
• Signed the informed consent form

Exclusion criteria

• Known history of allergy to hormonal component to be used in the study
• Male-to-female transgender who underwent orchiectomy
• Use of pre-exposure prophylaxis or post-exposure prophylaxis in the past 30 days
• Use of injectable FHT in the past 3 months
• Evidence of current hepatitis B virus infection (HBV) - i.e. hepatitis B surface antigen (HBsAg) positive
• Evidence of current hepatitis C virus infection (HCV) - i.e. HCV antibody positive
• 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
• Participant-reported active rectal infection requiring treatment
• History of gastrointestinal tract surgery that alter gastrointestinal tract and/or drug absorption
• Alcohol or drug use that, in the opinion of the investigator, would interfere with completion of study procedures