Merck announced results from a Phase 2a clinical trial evaluating the safety, tolerability and pharmacokinetics (PK) of six monthly oral doses, over 24 weeks, of islatravir, the companys investigational nucleoside reverse transcriptase translocation inhibitor, versus placebo for pre-exposure prophylaxis (PrEP) of HIV-1 infection in adults at low-risk of contracting HIV-1. After 24 weeks, once-monthly oral islatravir was generally well tolerated versus placebo. Most adverse events (AEs) were mild and there were no serious drug-related AEs in people who received islatravir. The levels of islatravir in peripheral blood mononuclear cells also remained above the pre-specified efficacy PK threshold for PrEP at both doses studied (60 mg and 120 mg) eight weeks after the last study dose. These data were shared as a late-breaking oral presentation during the virtual 11thInternational AIDS Society Conference on HIV Science (IAS 2021) and are a follow-up to the interim analysis that was presented earlier in 2021 at the virtual 2021 HIV Research for Prevention Conference.