Merck Pauses Enrollment in Phase 3 Clinical Trials for Islatravir HIV PrEP

Last night, Merck announced it would be pausing its phase 3 clinical trials for islatravir, an investigational, monthly oral drug for HIV pre-exposure prophylaxis (PrEP).

Merck is pausing enrollment in its IMPOWER 22 (MK-8591-022) and IMPOWER 24 (MK-8591-024) phase 3 trials upon recommendation from the islatravir PrEP external data monitoring committee (eDMC). During the pause, Merck will continue monitoring these and other studies; participants currently enrolled in the islatravir trials will still receive study medicine.

Merck investigators will implement additional monitoring measures for the study’s participants, including increased total lymphocyte and CD4+ T-cell assessments.

Islatravir for PrEP is a nucleoside reverse transcriptase translocation inhibitor for individuals at high risk of HIV-1 infection. Its long intracellular half-life enables it to be taken as infrequently as once a month.

The IMPOWER 22 and 24 clinical phase 3 trials are randomized, active-controlled, double-blind studies that evaluate the safety and efficacy of once-monthly oral islatravir, as compared to once-daily emtricitabine/tenofovir disoproxil fumarate (FTC/TDF).

IMPOWER 22 examines islatravir as PrEP in cisgender women at high risk of HIV infection. IMPOWER 24 compares islatravir to emtricitabine/tenofovir alafenamide (FTC/TAF) as well as FTC/TDF in cisgender men and transgender women who have sex with men.

Islatravir has multiple mechanisms of action and previously demonstrated high potency against HIV alone and in combination with other drugs. The promise of islatravir as a once-monthly PrEP is far more manageable than adhering to the typical once-daily PrEP regimens.