Therapeutic drug monitoring of tenofovir disoproxil and emtricitabine in oral HIV pre-exposure prophylaxis (PrEP) users who have undergone gastrointestinal surgery.

Objectives: Oral HIV pre-exposure prophylaxis (PrEP) is highly effective in preventing HIV, but its efficacy depends on adequate absorption of drug, which may decrease following gastrointestinal surgery.

Methods: Clinicians across eight Genito-urinary Medicine clinics in the United Kingdom submitted data on PrEP users with history of gastrointestinal surgery who were referred to a national complex PrEP multi-disciplinary team between June 2021 and April 2023. Anonymised data were submitted on demographics, surgical history, PrEP regimen, and results of therapeutic drug monitoring (TDM) and HIV screening tests. Descriptive analyses were performed in SPSS version 29.

Results: Nine cases described cis-gender men-who-have-sex-with-men (MSM) with median age of 47.4 years (IQR = 43 - 56.5) taking tenofovir disoproxil (TDF)/emtricitabine (FTC) daily (n = 8) or event-based (n = 1) as PrEP. Median time between PrEP initiation and TDM was 53 days (IQR = 8.5-1705). The mean (±SD) trough concentration of tenofovir (TFV) and FTC were 90.2 ± 27.7 ng/mL and 76.0 ± 45.9 ng/mL, respectively. All patients had a negative HIV test at follow-up.

Conclusions: Plasma trough concentrations of TFV observed in our cohort taking TDF/FTC were above the expected concentrations associated with PrEP efficacy as previously described in the literature, suggesting that PrEP can be safely given in this population, with TDM used for reassurance.