Merck and Gilead Sciences have resumed a Phase II clinical trial of a weekly oral HIV treatment regimen that combines a lower dose of Merck’s experimental nucleoside reverse transcriptase translocation inhibitor islatravir and Gilead’s new HIV capsid inhibitor Sunlenca (lenacapavir). In December 2021, the Food and Drug Administration placed a hold on islatravir trials after study participants showed declines in CD4 and total lymphocyte counts. Merck scientists determined that the islatravir doses used in those trials were too high, and people who took lower doses did not have notable lymphocyte changes. A 0.25 milligram dose of islatravir is now being tested with Pifeltro (doravirine) as a once-daily regimen, and a 2 mg dose is being studied with oral Sunlenca as a once-weekly regimen. In the latter trial, people who have taken the daily Biktarvy pill (bictegravir/tenofovir alafenamide/emtricitabine) for at least six months and have an undetectable viral load will be randomized to either stay on Biktarvy or switch to weekly low-dose islatravir plus Sunlenca pills.