Is event-driven PrEP dosing for HIV as effective as daily dosing?
EVIDENCE-BASED ANSWER:
Probably, although there are no head-to-head trials comparing the 2 dosing regimens. Event-driven pre-exposure prophylaxis (PrEP) dosing reduces HIV conversion by 86% compared to placebo (strength of recommendation [SOR]: B, large randomized controlled trial [RCT]). Daily PrEP reduces HIV conversion by 44% to 86% (SOR: B, based on open-label RCTs).
Event-driven PrEP regimens may be associated with lower adherence when compared with daily PrEP regimens (average of 70% for event-driven PrEP vs average of 92% for daily PrEP) (SOR: B, based on open-label and cohort trials). Event-driven PrEP regimens have lower medication costs, and they are associated with no difference in the rate of sexually transmitted infections (STIs) (SOR: B, based on prospective cohort studies). Patients may prefer them to daily regimens (75% choose event-driven PrEP vs 25% choose daily PrEP) (SOR: B, based on the preponderance of prospective cohort studies with conflicting results).
In an open-label prospective cohort trial in Belgium, at-risk patients chose between using event-driven (N = 44) and daily (N = 135) PrEP. Analysis was conducted for both high-risk HIV exposure days (defined as condomless anal receptive intercourse with a new or HIV-positive steady partner with a detectable viral load) and low-risk HIV exposure days (consistent condom use or condomless anal intercourse with a steady partner who is HIV-negative). Over 18 months, lower adherence was demonstrated with event-driven PrEP than with daily PrEP for high-risk days (88% [95% CI, 86%-90%] vs 97.5% [95% CI, 97%-98%]; P < .0001) and also for low-risk days (42% [95% CI, 40%-45%] vs 96% [95% CI, 95%-96%]; P < .0001).6 Researchers diagnosed no new HIV infections in any participant, and the incidence of STIs was the same in both groups.
A third open-label trial evaluated adherence among 178 South African women randomized to event-driven or daily PrEP and found lower sexual event coverage with event-driven PrEP (52% vs 75%; odds ratio = 2.76; 95% CI, 1.68-4.53; P < 0.0006). Four women in each group seroconverted to HIV positive.7
Drug costs, patient preferences, and STI risk are important considerations
,Several of the above trials reported use of fewer pills in the event-driven groups, with lower drug costs.2,5,7 A large prospective cohort trial of men who have sex with men (N = 1049) with an average of 10 sexual partners found that most (76%) opted for event-driven PrEP.8 Researchers also reported no difference in STI rates (RR = 1.24 for “at least 1 bacterial STI”; 95% CI, 0.84 to 1.81).8 However, a smaller, open-label prospective cohort trial (N = 200) found that more participants chose daily PrEP than event-driven PrEP (76.5% vs 23.5%), although almost all said they would change their dosing regimen in the next year.9
Recommendations from others
In 2019, the World Health Organization recommended oral PrEP as an additional prevention choice for people at substantial risk for HIV infection and stated that different dosing strategies offer users flexibility, choice, and convenience.10 Also in 2019, the US Preventive Services Task Force published a recommendation that clinicians offer PrEP with effective antiretroviral therapy to patients at high risk for HIV acquisition. They did not specify which regimen to offer.11
Editor’s takeaway
While there are theoretical reasons why event-driven PrEP might not work as well as daily PrEP, we have 1 RCT that suggests the real-world outcomes are similar. Given the apparent effectiveness of either option, the best choice is the one the patient will use. JFP
