US FDA and Japan approve new once-daily oral HIV combination of doravirine/islatravir (IDVYNSO)

21 April 2026. Related: Early access, Antiretrovirals.

Simon Collins, HIV i-Base

On 21 April 2026, the US FDA approved a new two-drug fixed combination of doravirine/islatravir 100 mg/0.25 mg (DOR/ISL). [1]

The combination was also approved six weeks earlier in Japan on 6 March 2026, but with little press coverage. [2]

This single tablet regimen (STR) is a once-daily oral pill with an indication as a switch option in people who currently have undetectable viral load (<50 copies/mL) on current ART.

Other criteria include:

• Not having a history of drug resistance to either doravirine or islatravir.
• Not using it with drugs that are strong cytochrome P450 (CYP)3A enzyme inducers.
• Not to use with either lamivudine (3TC) or emtricitabine (FTC).

Approval was based on 48-week results from the randomised phase 3 Merck 051 and 052 non-inferiority switch studies.

The open-label 051 study randomised 551 people (2:1) on stable ART to either DOR/ISL or to continue current ART.  The double-blind 052 study randomised 513 people (2:1) on stable B/F/TAF to either switch to DOR/ISL or remain on current ART. At week 48 viral load was detectable >50 copies/mL in 1% vs 1% in 051 and in 1% vs 5% in 052, in DOR/ISL vs control arms respectively.

Although these studies reported generally good tolerability with few serious side effects, DOR-ISL doesn’t provide cover for hepatitis B infection.

DOR/ISL is manufactured and marketed in the US by Merck/MSD with the tradename IDVYNSO.

For full details please see the full prescribing information.

comment

Latest data on DOR/ISL reported at CROI 2026 in February also included the first results of a randomised phase 3 study in treatment-naive participants.

Some of the discussions at the meeting highlighted the importance of monitoring for hepatitis B. [3]

No information or timeline is available about registration with the EMA in the EU nor with the MHRA in the UK. However, the EMA might want the submission to include 96-week data rather than the 48-week data accepted by the FDA.

References

1. Merck.MSD press release. FDA Approves Merck’s Once-Daily IDVYNSO (doravirine/islatravir). 21 April 2026.
   https://www.merck.com/news/fda-approves-mercks-once-daily-idvynso-doravirine-islatravir
2. Pharma Japan. Japan Approves MSD’s HIV Combo Idvynso. (9 March 2026).
   https://pj.jiho.jp/article/254915
3. CROI 2026: Investigational HIV combinations – daily, weekly, 4- and 6-monthly… HTB (15 April 2026).
   https://i-base.info/htb/53695