The next-generation non-nucleoside reverse transcriptase inhibitor (NNRTI) doravirine (formerly MK-1439) showed potent antiretroviral activity and good tolerability in combination with tenofovir/FTC (the drugs in Truvada) in a dose-finding study presented at the 21st Conference on Retroviruses and Opportunistic Infections (CROI) last week in Boston.
NNRTIs are generally well tolerated and well suited for first-line HIV treatment, but as a class they are susceptible to resistance. Pre-clinical studies showed that Merck’s doravirine has a distinct resistance profile and remains active against HIV with common NNRTI resistance mutations including K103N and Y181C.
As reported at last year’s CROI, doravirine reduced HIV viral load by about 1.3 log in a seven-day monotherapy study. Doravirine is processed by the CYP3A4 enzyme, but it is neither a CYP3A4 inducer nor inhibitor, so it is not expected to have major drug interaction concerns.
Javier Morales-Ramirez from Clinical Research Puerto Rico reported late-breaking findings from a phase 2b study evaluating the safety and efficacy of various doses of doravirine versus efavirenz (Sustiva) for initial antiretroviral therapy.
This study included 208 treatment-naive people living with HIV from North America, Europe and Asia. More than 90% were men, 74% were white, 20% were black and the median age was 35 years. At baseline, the median CD4 cell count was approximately 375 cells/mm3 and 13% had received an AIDS diagnosis. Study participants were stratified by whether their viral load was above (about 30%) or below 100,000 copies/ml; median HIV RNA was approximately 4.5 log10.
Morales-Ramirez reported 24-week results from part 1 of the study, which will continue for a total of 96 weeks. In this part, participants were randomly allocated into five equal-sized arms receiving doravirine at doses of 25, 50, 100 or 200mg once daily, or else efavirenz once daily, all in combination with tenofovir/FTC.
At 24 weeks, 76.4% of participants taking doravirine had viral load below 40 copies/ml compared with 64.3% of people taking efavirenz. Response rates were similar across doravirine doses (25mg: 80.0%; 50mg: 76.2%; 100mg: 71.4%; 200mg: 78.0%). More than 80% of participants in all treatment arms reached the less stringent virological response threshold of <200 copies/ml.
Both doravirine and efavirenz worked better for people with lower pre-treatment viral load in an ad hoc analysis. For people with <100,000 copies/ml at baseline, response rates (<40 copies/ml) ranged from 83 to 89% with doravirine compared with 74% with efavirenz. For those with >100,000 copies/ml, response rates ranged from 50 to 91% with doravirine vs 54% with efavirenz.
Median CD4 cell gains were 137 cells/mm3 for all doravirine arms combined and 121 cells/mm3 for the efavirenz arm.
Doravirine was generally safe and well tolerated. People taking doravirine were less than half as likely as people taking efavirenz to experience serious adverse events (3.0% across all doravirine arms vs 7.1% with efavirenz) or to stop treatment for this reason (2.4 vs 4.8%). Four people taking doravirine and two people taking efavirenz discontinued due to adverse events considered to be drug-related.
The most common side-effects were dizziness (3.6% with doravirine vs 23.8% with efavirenz), abnormal dreams (9.0 vs 7.1%), diarrhoea (4.8 vs 9.5%), nausea (7.8 vs 2.4%) and fatigue (6.6 vs 4.8%). Other central nervous system (CNS) adverse events of interest included insomnia (5.4 vs 7.1%), nightmares (1.2 vs 9.5%) and hallucinations (0.6 vs 2.4%). Overall, 20.5% of people taking doravirine reported at least one CNS side-effect, compared with 33.3% of people taking efavirenz.
People taking doravirine had more favourable lipid profiles and less frequent liver enzyme (ALT and AST) elevations compared with people taking efavirenz.
The researchers concluded that doravirine demonstrated potent antiretroviral activity in treatment-naive patients, a favourable safety and tolerability profile, and fewer drug-related adverse events compared with efavirenz.
Based on these findings, the 100mg once-daily dose was selected for future development and will be used in part 2 of this study, a dose-confirmation analysis that will enrol an additional 120 participants.
In the discussion following the presentation, Daniel Kuritzkes from Harvard Medical School noted that sometimes it takes longer for viral load to go down in people who start with a high level, so with further follow-up past 24 weeks doravirine may no longer look less effective in such individuals.