P062 Therapeutic drug monitoring in oral HIV pre-exposure prophylaxis users with a history of bariatric surgery – a case series

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Introduction Oral HIV pre-exposure prophylaxis (PrEP) with tenofovir disoproxil fumarate (TDF) and emtricitabine (FTC) is highly effective in preventing HIV when taken adequately. Plasma concentration for TDF of >40ng/mL has been reported to be highly predictive of protection from HIV acquisition.1 The prevalence of obesity is increasing globally with growing numbers of people undergoing bariatric surgery including gastric sleeve, Roux-en-Y gastric bypass (RYGB), or gastric banding.2 Drug absorption may decrease following bariatric surgery and there are limited data on PrEP drug concentrations and efficacy following this intervention. Methods We included PrEP-users with previous bariatric surgery who were referred to a national complex PrEP clinic between June 2021 and March 2023. We collected data on demographics, bariatric surgery history, PrEP regimen, plasma TDF/FTC trough concentrations, and HIV antibody test results via retrospective case-notes review. We undertook descriptive analyses in SPSS version 29. Results We included eight cases (Table 1); all were cis-gender men-who-have-sex-with-men [mean age = 46.6 years [standard deviation (SD) = 11.9]] taking TDF/FTC as a daily dose (DD) or event-based dose (EBD). Median time between PrEP initiation and therapeutic drug monitoring was 66 days [interquartile range (IQR) = 5.3 - 1623]. Mean plasma trough concentrations of TDF and FTC were 85.9ng/mL (SD=27.5) and 59.2ng/mL (SD=45.1) respectively. All patients had a negative HIV antibody test at follow-up after commencing PrEP (median 532 days, IQR = 111–1759). Discussion Plasma trough concentrations of TDF observed in our cohort with either daily or event-based TDF/FTC were above the expected concentrations associated with PrEP efficacy1. This suggests that these bariatric interventions do not affect drug exposure or raise concerns related to decreased efficacy of TDF/FTC for PrEP. It is therefore important to ensure that PrEP is considered in people who have had bariatric surgery at high risk of HIV acquisition, and TDM used for reassurance. References Donnell D, Baeten JM, Bumpus NN, Brantley J, Bangsberg DR, Harberer JE, et al. HIV protective efficacy and correlates of tenofovir blood concentrations in a clinical trial of PrEP for HIV prevention. J Acquir Immune Defic Syndr. 2014;66(3):340–8. Lazzati A. Epideminology of the surgical management of obesity. J Visc Surg [Internet]. 2023 Apr;160(2):S2–6. Available from: https://linkinghub.elsevier.com/retrieve/pii/S1878788622001783