Merck, known as MSD outside of the United States and Canada, announced that the company will initiate a new Phase 3 clinical program with once-daily islatravir for the treatment of people with HIV-1 infection. These new Phase 3 studies will evaluate a once-daily oral combination of doravirine 100 mg and a lower dose of islatravir (DOR/ISL). One study will evaluate DOR/ISL in previously untreated adults with HIV-1 infection and two studies will evaluate DOR/ISL as a switch in antiretroviral therapy (ART) in adults with HIV-1 infection who are virologically suppressed.

The U.S. Food and Drug Administration (FDA) has reviewed and agreed with this plan. The investigational new drug application (IND) for the once-daily oral DOR/ISL treatment program remains under a partial clinical hold for any studies that would use doses higher than the dose to be studied in the new Phase 3 program. Refer here for more information on the islatravir clinical hold.

The Phase 2 clinical trial (NCT05052996) evaluating an investigational oral once-weekly combination treatment regimen of islatravir and Gilead’s lenacapavir in adults with HIV-1 infection who are virologically suppressed will resume under an amended protocol with a lower dose of islatravir. The IND under which the islatravir + lenacapavir once-weekly treatment regimen is being investigated remains under a partial clinical hold for any studies that would use weekly oral islatravir doses higher than the doses considered for the revised clinical program. Islatravir and lenacapavir, in combination, are investigational and not approved for use. The safety and efficacy of this combination has not yet been established.

Additionally, after careful evaluation and analysis, Merck will discontinue the development of once-monthly oral islatravir for PrEP. Participants in the ongoing Phase 3 PrEP once-monthly oral studies will continue to be monitored. The company remains committed to developing compounds for long-acting HIV prevention and believes in the potential of the nucleoside reverse transcriptase translocation inhibitor (NRTTI) mechanism. A Phase 1b study in adults with HIV-1 infection assessing MK-8527, a novel NRTTI candidate, will commence shortly (NCT05494736). Merck will continue to engage with key stakeholders as it works to help address the unmet need in HIV prevention.

“We are grateful to the study investigators and the many participants in the trials of islatravir. Following extensive evaluations and consultation with FDA, we are pleased to be able to initiate our new Phase 3 clinical program to evaluate islatravir for the treatment of HIV-1 infection,” said Dr. Eliav Barr, senior vice president and head of global clinical development, chief medical officer, Merck Research Laboratories. “We continue to believe in the potential of the NRTTI mechanism and we are evaluating additional candidates with the goal of helping to address unmet needs in HIV prevention. As part of this, we are pleased to continue our partnership with the Bill & Melinda Gates Foundation as we continue to evaluate potential long-acting PrEP opportunities.”