Islatravir plus doravirine dual ART: 144 week follow-up from phase 2 study
Simon Collins, HIV i-Base
Extended results from the early phase 2 study daily oral islatravir plus doravirine were presented at EACS 2021 in an oral presentation. This dual combination is already in phase 3 development. 
This was initially a randomised dose-finding study in 120 treatment naive participants with 30 people in each of the 0.25, 0.75, and 2.25 mg groups (used with 3TC/TDF) and a control arm of doravirine/3TC/TDF.
Several efficacy and safety results at 96-week were presented at Glasgow 2020, CROI 2021 and IAS 2021 and generally were similar at 144 weeks (when participants had received 60-84 weeks on dual islatravir + doravirine).
By snapshot analysis, 72% (65/90) of the combined islatravir participants had viral suppression <50 copies/mL, with 83% (25/30) in the original dose-selected 75 mg islatravir arm, compared to 77% (24/30) in the control arm.
Viral failure was rare, with viral load >50 copies/mL in 7 vs 1 participants in the combined vs control arms. Approximately 20% in each group (18/90 vs 6/30) had missing data at week 144, with most of those in the islatravir arms not related to study drug.
Of the 7 who discontinued with protocol defined viral failure (confirmed VL >50 copies/mL), all had viral load < 80 copies/mL. Of these 5/7 had baseline viral load >100,000 copies/mL. There was only one non-responder (in the higher dose islatravir arm).
A recent safety analysis of ongoing islatravir studies has reported reductions in mean total lymphocyte counts (and sometimes CD4 counts), although these are still within normal ranges.
Limited details are available, but this also included PrEP studies using islatravir monotherapy in HIV negative people. 
- Molina J-M. Efficacy and safety of islatravir in combination with doravirine through 144 weeks for treatment-naïve adults with HIV-1 infection in a phase 2b trial. EACS 2021, oral abstract session, 28 October 2021, 3-4 pm. Oral abstract OS1/5.
- MSD/Merck stop once-weekly NNRTI MK-8507: islatravir studies continue with closer monitoring. HTB (19 November 2021).
This report was first posted on 14 November 2021. It was updated on 26 November to include the comments.