Islatravir, a long-acting antiretroviral from Merck, has hit a snag after clinical trial participants experienced falling white blood cell counts. Islatravir is being tested as a component of once-weekly HIV treatment and as a once-monthly pill or once-yearly implant for pre-exposure prophylaxis (PrEP). Some HIV-positive people in treatment trials saw a drop in their CD4 T-cell counts, while HIV-negative volunteers in PrEP trials experienced a decrease in total lymphocytes. In December, the Food and Drug Administration placed a partial clinical hold on seven studies of daily oral islatravir plus doravirine and a full clinical hold on six studies of islatravir PrEP and injectable islatravir. Merck had already halted studies of islatravir plus its experimental drug MK-8507, and Merck and Gilead Sciences also paused a study of islatravir plus lenacapavir. Speaking with advocates, Michael Robertson, MD, of Merck Research Laboratories, said researchers are working to understand what’s causing the side effect and whether islatravir can move forward.
Treatment: Islatravir on Hold
Islatravir, a long-acting antiretroviral from Merck, has hit a snag after clinical trial participants experienced falling white blood cell counts.