O13.2 Predictors of PrEP adherence among men who have sex with men in Amsterdam, the Netherlands

Background Adherence is key to the effectiveness of pre-exposure prophylaxis (PrEP) for prevention of HIV. Knowing what factors are associated with adherence could help clinicians focus counselling efforts on individuals less likely to adhere. Methods Men who have sex with men (MSM) using daily PrEP within the Amsterdam PrEP demonstration Project (AMPrEP) at the Public Health Service of Amsterdam, provided dried blood spots (DBS) 12 and 24 months after PrEP initiation. From these DBS, we determined intracellular tenofovir diphosphate concentrations [TFV-DP] to measure adherence; [TFV-DP]>700 fmol/punch is considered sufficient. We assessed associations between [TFV-DP] and sociodemographic and behavioural characteristics among MSM using daily PrEP using multivariable linear regression. Results Of 263 participants who attended their 12- or 24-month study visit whilst using daily PrEP, 257 (97.7%) provided DBS at one or both visits (492 DBS in total). Median [TFV-DP] was 1299 (IQR 1021–1627) fmol/punch (12 months: 1332 [1087–1687]; 24 months: 1248 [929–1590]). Higher [TFV-DP] were associated with: older age (+95 fmol/punch/10 years; p=0.0012), not identifying as exclusively homosexual (+142 fmol/punch; p=0.042), condomless anal sex with a casual partner 6 months prior to PrEP initiation (+159 fmol/punch; p=0.0089), and using an extended mobile application (vs. standard mobile application; +143 fmol/punch; p=0.020). Lower [TFV-DP] were associated with longer duration of PrEP use (24 vs. 12months; -100 fmol/punch; p=0.0019). Number of sex partners, diagnosed sexually transmitted infections (STI), and chemsex were not associated with [TFV-DP]. Conclusion Overall [TFV-DP] were high among MSM, indicating good adherence, especially among participants who are older, not identifying as exclusively homosexual, and those who reported condomless anal sex with a casual partner 6 months prior to PrEP initiation. We recommend to pay extra attention to adherence when counselling younger PrEP users and those who have been using PrEP for a longer period.