Merck /zigman2/quotes/209956077/composite MRK +0.22% said Tuesday it is launching a new Phase 3 trial of 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)," the company said in a statement. Certain participants currently enrolled in once-daily treatment studies with with DOR 100 mg/ISL 0.75 mg will have the option of transitioning to a new study with the lower islatravir dose. The new study has been reviewed by the U.S. Food and Drug Administration which has endorsed the plan. The company said a Phase 2 study evaluating an investigational oral once-weekly combination treatment regimen of islatravir and Gilead's /zigman2/quotes/210293917/composite GILD +1.29% 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," said the statement. Merck is discontinuing a trial of once-monthly oral islatravir for PrEP. Participants will continue to be monitored, however, as the company still believes in the potential of long-acting HIV prevention. "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," said Dr. Eliav Barr, senior vice president and heald of global clinical development, chief medical officer, Merck Research Laboratories, in a statement. Shares were down 0.4% premarket, but have gained 13% in the year to date, while the Dow Jones Industrial Average [s djia] has fallen 15%.