The FDA approved Merck $MRK's once-daily, two-drug HIV pill Idvynso on April 21, giving clinicians a new option for adults who are already virologically suppressed on a stable antiretroviral regimen.
Eligible patients must already have HIV-1 RNA below 50 copies per mL, a stable treatment history free of virologic failure, and no documented resistance to doravirine; the fixed-dose tablet — 100 mg doravirine plus 0.25 mg islatravir — is authorized only as a switch option, not for initiating HIV therapy. Merck said the pill will be available in pharmacies after May 11.
Merck described Idvynso as the first non-integrase strand transfer inhibitor (INSTI), tenofovir-free, once-daily complete two-drug regimen to demonstrate non-inferior efficacy against a three-drug regimen in a head-to-head Phase 3 trial. That trial compared Idvynso against Gilead $GILD's Biktarvy, a three-drug combination of bictegravir, emtricitabine, and tenofovir alafenamide. At week 48, 1% of participants in each group had a viral load at or above 50 copies per mL.
A second Phase 3 trial compared Idvynso against a range of baseline antiretroviral regimens. At week 48, 1% of participants switched to Idvynso had detectable viral load, compared with 5% who remained on their prior therapy. Across both trials, a total of 708 participants received Idvynso.
The approval closes a difficult chapter for islatravir, one of Idvynso's two components. Islatravir's path to approval was turbulent: Prismnews noted that declining lymphocyte and CD4+ T-cell counts in certain study participants prompted regulators to impose a clinical hold on the drug in December 2021. Development resumed only after Merck reformulated the drug at a reduced dose, eventually producing the pairing that won Tuesday's approval. Doravirine, the regimen's other component, was already sold in the U.S. under the brand names Pifeltro and Delstrigo.
The most common adverse reactions reported in at least 2% of participants in either trial were diarrhea, dizziness, fatigue, abdominal distension, headache, and weight increase. Severe skin reactions, including Stevens-Johnson syndrome and toxic epidermal necrolysis, have been reported with doravirine-containing regimens. Idvynso is contraindicated with strong CYP3A enzyme inducers and with lamivudine or emtricitabine.
National Institutes of Health data cited by Reuters put the current global HIV burden at roughly 40.8 million people, with an estimated 1.3 million additional cases arising each year.
Merck is also pursuing islatravir in Phase 3 studies alongside Gilead's lenacapavir, exploring whether the pairing could eventually support a once-weekly oral dosing schedule.