Objectives Doxycycline prophylaxis shows promise for bacterial sexually transmitted infection (STI) prevention, but data primarily come from high-income countries. This study assessed awareness, willingness and factors associated with willingness to use doxycycline for bacterial STI prevention among men who have sex with men (MSM) using HIV pre-exposure prophylaxis (HIV-PrEP) in Vietnam.

Methods Between 25 January and 4 February 2024, a cross-sectional study recruited males aged ≥18 years who reported having sex with men in the past 12 months from 11 HIV-PrEP clinics in Hanoi and Ho Chi Minh City. Self-administered surveys were conducted, and multivariable logistic regression was applied to identify factors associated with willingness to use doxycycline prophylaxis.

Results Among 350 participants, the median age was 25 (IQR 21–30), and 10.6% self-reported a bacterial STI diagnosis in the past 12 months. In the previous 6 months, the median number of sex partners was 2 (IQR 1–4), 53.1% reported condomless anal sex. Awareness of doxycycline was low (20.2%; 65/322); however, 75.4% (264/350) expressed willingness to use it, with 63.6% (168/264) preferring doxyPrEP. Participants who disclosed HIV-PrEP use to all sex partners (adjusted OR (aOR) 4.17; 95% CI 1.84, 9.46) and those with higher perceived STI risk (aOR 1.12; 95% CI 1.03, 1.22) were more likely to report willingness to use doxycycline prophylaxis. Concerns about daily medication (aOR 0.43; 95% CI 0.24, 0.81) and fear of judgement from peers (aOR 0.41; 95% CI 0.21, 0.81) were associated with lower willingness.

Conclusions Knowledge of doxycycline prophylaxis among MSM on HIV-PrEP in Vietnam was low. However, most expressed willingness to use it, with two-thirds preferring doxyPrEP. Findings highlight the need to disseminate information on doxycycline prophylaxis for bacterial STI prevention, monitoring the usage and evaluating comparative effectiveness of doxyPEP and doxyPrEP to guide implementation efforts in Vietnam.