Merck announced a pause in enrollment for the IMPOWER 22 (MK-8591-022) and IMPOWER 24 (MK-8591-024) Phase 3 clinical studies evaluating investigational, once-monthly, oral islatravir (ISL), a nucleoside reverse transcriptase translocation inhibitor, for pre-exposure prophylaxis (PrEP) in people at high risk of HIV-1 infection.

At the recommendation of the ISL PrEP external data monitoring committee (eDMC), Merck is pausing enrollment for the IMPOWER 22 and IMPOWER 24 trials while the company conducts further analyses of these and other ongoing studies. Participants already enrolled in the trials will continue to receive the study medicine. Informed by the recommendations of the PrEP eDMC, Merck is implementing additional monitoring measures for study participants, including increasing the frequency of total lymphocyte and CD4+ T-cell assessments. Investigators have been informed of these actions.

“We continue to apply learnings from our HIV program as we move forward with the development of islatravir in both treatment and PrEP,” said Dr. Joan Butterton, vice president, infectious diseases, Global Clinical Development, Merck Research Laboratories. “Merck remains committed to developing tools to help address unmet needs in HIV treatment and prevention to contribute to the global effort against the ongoing HIV epidemic.”

About IMPOWER 22 (MK-8591-022) and IMPOWER 24 (MK-8591-024)

The IMPOWER 22 clinical trial is a Phase 3, randomized, active-controlled, double-blind clinical study to evaluate the efficacy and safety of oral islatravir once-monthly compared to once-daily emtricitabine/tenofovir disoproxil fumarate (FTC/TDF) as pre-exposure prophylaxis (PrEP) in cisgender women at high risk for HIV-1 Infection.

The IMPOWER 24 clinical trial is a Phase 3, randomized, active-controlled, double-blind clinical study to evaluate the efficacy and safety of oral islatravir once-monthly as PrEP compared to once-daily FTC/TDF or emtricitabine/tenofovir alafenamide (FTC/TAF) in cisgender men and transgender women who have sex with men, and are at high risk for HIV-1 infection