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# Merck Reports Positive Data on HIV Trials
- URL: https://www.fdaweb.com/merck-reports-positive-data-on-hiv-trials/
- Published: 2025-03-12T12:00:00.000Z
- Updated: 2026-09-14T14:55:09.000Z
- Author: David McFarland
- Tags: Drugs, #legacy-id-D5158807

Merck is announcing “positive results” from two pivotal Phase 3 trials of the investigational, once-daily, oral, two-drug regimen of doravirine/islatravir (DOR/ISL (100mg/0.25mg) in certain adults with HIV-1 infection that is virologically suppressed. It says an NDA will be submitted to FDA by mid-year.

The trials evaluated patients whose infection is virologically suppressed on bictegravir/emtricitabine/tenofovir alafenamide (trial [MK-8591A-052](https://cts.businesswire.com/ct/CT?id=smartlink&url=https%3A%2F%2Fclinicaltrials.gov%2Fstudy%2FNCT05630755&esheet=54223136&newsitemid=20250312706063&lan=en-US&anchor=MK-8591A-052&index=1&md5=d962319798a591d93c498e4e23a89f2f&ref=fdaweb.com) ) or antiretroviral therapy (trial [MK-8591A-051](https://cts.businesswire.com/ct/CT?id=smartlink&url=https%3A%2F%2Fclinicaltrials.gov%2Fstudy%2FNCT05631093%3Fterm%3Dislatravir%26page%3D2%26rank%3D20&esheet=54223136&newsitemid=20250312706063&lan=en-US&anchor=MK-8591A-051&index=2&md5=9f12d7e4233e638166ba99975cc400aa&ref=fdaweb.com)). “In both trials, DOR/ISL met the primary efficacy success criterion for non-inferiority to comparator antiretroviral therapies and primary safety objectives at Week 48,” Merck says. 

The clinical trial program suffered a setback in 2021 when FDA placed clinical hold on the IND and other related INDs due to observations of decreases in total lymphocyte and CD4+ T-cell counts in some participants receiving islatravir in clinical studies, Merck said at the time ([see story](http://fdaweb.com/login.php?sa=v&aid=D5150760&cate=&stid=%241%24Qi..Za0.%24pssiwThyOI2Q3F0AvquuR%2F&ref=fdaweb.com)). The hold was lifted in 9/2022, at which time Merck announced it was also discontinuing the development of once-monthly oral islatravir for HIV-1 pre-exposure prophylaxis.

Merck says islatravir is an investigational nucleoside reverse transcriptase translocation inhibitor that is designed to block HIV-1 replication by multiple mechanisms. Doravirine is currently approved and marketed as Pifeltro for combination use with other antiretroviral agents for treating HIV-1 infection. It is also approved under the brand name Delstrigo (doravirine, lamivudine, and tenofovir disoproxil fumarate) as a complete regimen for treating HIV-1 infection.