13 of Merck’s Islatravir studies placed on clinical hold by FDA

Decreased total lymphocyte and CD4+T cell counts related to islatravir result in FDA clinical hold.



Merck has announced that the FDA has placed a clinical hold on the Investigational New Drug (IND) applications involving the HIV investigational drug islatravir. The hold applies to islatravir (MK-8591) oral and implant formulations for HIV-1 pre-exposure prophylaxis (PrEP), the HIV-1 injectable formulation for prophylaxis and treatment as well as the HIV-1 once daily oral doravirine/islatravir (DOR/ISL) treatment. The FDA directive comes after a decrease in total lymphocyte and CD4+T cell count was observed in studies where participants were receiving islatravir. As part of the hold, new islatravir studies are not permitted and participants receiving islatravir on PrEP studies will no longer receive treatment. Nevertheless, participants will be offered an approved oral PrEP treatment and their lymphocyte and CD4+T cell counts will continue to be monitored.


Participants who initiated treatment on DOR/ISL studies will continue treatment on partial clinical hold. All screening and randomisation has been halted for the DOR/ISL treatment arm. Merck Research Laboratories Global Clinical Development infectious diseases vice-president Dr Joan Butterton stated, “Merck continues to investigate the potential of islatravir and nucleoside reverse transcriptase translocation inhibitors and remains committed to helping to address unmet needs in HIV treatment and prevention.” A total of six studies have been placed on full clinical hold while seven are placed on partial clinical hold. Additionally, Gilead and Merck’s Phase 2 study where both islatravir and lenacapavir were administered to virologically supressed HIV participants has discontinued treatment. Both companies are committed to their collaboration to ensure that the needs of people living with HIV are met.