Merck & Co Inc paused enrolment on 6 December for two Phase 3 trials of its lead investigational treatment for HIV – a little more than two weeks after stopping dosing in a Phase 2 study of an HIV combination therapy. The measures were taken on the recommendation of the trials’ respective data monitoring committees. They affect MK-8507, a non-nucleoside reverse transcriptase inhibitor, and islatravir, a nucleoside reverse transcriptase translocation inhibitor. In both cases, the actions were taken in relation to total lymphocyte and CD4+ T cell counts in patients.