HIV: Could Another Two-Drug Regimen Be on the Horizon?

Heather Boerner

July 20, 2021

Headache was the most common adverse event (AE) people experienced in 72 weeks of taking the once-daily investigational two-drug HIV treatment islatravir (ISL; Merck) plus doravirine (DOR; Merck), and those AEs were short-lived and mild, according to a safety analysis presented at the International AIDS Society (IAS) Conference 2021.

That finding, combined with other data showing few changes in metabolic markers, is potentially good news for people living with HIV, inasmuch as two-drug regimens generally have fewer side effects than traditional three- or four-drug regimens, said Jean-Michel Molina, MD, PhD, of Sant-Louis and Lariboisière Hospitals, Paris, France, who previoualy presented efficacy data on the combination at the HIV Glasgow 2020 Virtual Conference.

"At this point, it's encouraging," Molina told Medscape Medical News. "Safety is good, efficacy seems good. But the data are limited, and it's too early to tell."

If it makes it to the clinic, IS/DOR would be the fourth two-drug regimen approved for HIV treatment, following the US Food and Drug Administration approval of dolutegravir/lamivudine (Dovato), dolutegravir/rilpivirine (Juluca), and the monthly injectable cabotegravir long-acting/rilpivirine long-acting (Cabenuva).

DOR, a nonnucleoside reverse transcriptase inhibitor (NNRTI), is currently approved and is part of the three-drug single-pill regimen Delstrigo (doravirine/lamivudine/tenofovir disoproxil fumarate, DOR/3TC/TDF, Merck). ISL is still under development for treatment and prevention. Molina had previously presented data showing that 81.1% of people living with HIV maintained undetectable viral loads (defined as <50 copies/mL) compared to 80.6% of people who continued treatment with DOR/3TC/TDF. Data on ISL/DOR vs DOR/3TC/TDF for people new to HIV treatment were published in The Lancet HIV in May.

The ISL/DOR trial was designed to assess the safety of three doses of ISL with 100 mg of DOR ― 0.25 mg, 0.75 mg, and 2.25 mg ― as a daily treatment. The investigators randomly assigned 29, 30, and 31 participants, respectively, to each of the dual-therapy arms and 31 people to the DOR/3TC/TDF arm after a 24-week lead-in course of DOR/3TC/TDF. At week 60, everyone in the two-drug arms received 0.75 mg of ISL with DOR.

At HIV Glasgow, Molina didn't present details about the safety profile of the two-drug combination. Douglas Cunningham, DO, a primary care provider at Pueblo Family Physicians, in Phoenix, Arizona, presented such data at IAS 2021. What he showed was that over the first 96 weeks of the trial, there were a total of 118 AEs among the 90 participants in the ISL plus DOR arms and 42 among the 31 participants in the three-drug regimen arm, but there were only seven drug-related AEs for people in the ISL plus DOR arm, and all of those occurred during the first 48 weeks. There were none from weeks 48 to 96.

In total, there were no drug-related serious AEs for ISL/DOR; there was one in the DOR/3TC/TDF arm. The most common AE was headache, which occurred in a total of 10 participants in the ISL/DOR arms. There were nine cases of vitamin D deficiency, eight cases of nausea, seven cases of arthralgia, diarrhea, sinus pain, and vomiting, and six cases each of anxiety and rash. Four people experienced pain in their extremities.

In the three-drug combination arm, side effects were far fewer — just 18 occurred in at least 10% of participants. The most common AE among people on the three-drug combination was diarrhea, which occurred in six participants. Nausea occurred in three; vomiting and headache, in two; and there was one instance each of vitamin D deficiency, arthralgia, sinus pain, rash, and pain in extremities.

"The majority of these events were mild, transient, and not related to study drug," Cunningham said.

Three ISL/DOR participants experienced an increase in fasting triglyceride level of >500–1000 mg/dL, and six patients experienced grade 4 changes in creatine kinase level of ≥20 IU/L. Cunningham said that all but one of the cases of an increase in creatinine level were the result of physical exertion by the participants, and all of those changes were found to have resolved at future visits. The bottom line is that the two-drug combination was safe.

"In the islatravir and doravirine arm, there were no serious drug related serious AEs and no discontinuations due to drug-related AEs from week 48 to week 96," said Cunningham. "Islatravir in combination with doravirine was generally well tolerated through week 96 with few drug-related AEs."

Still, the value of this combination is unclear for Laura Waters, MD, consulting physician in HIV and sexual health at Central and Northwest London NHS Trust. She pointed out that the data are preliminary and that islatravir hasn't yet been shown to lessen the chances of development of treatment-resistant mutations — a big deal for two-drug regimens, inasmuch as early attempts at using only two drugs resulted in incomplete suppression of the virus and resistance. Merck is planning a study of the combination in heavily pretreated individuals.

Merck presented data at IAS on another NNRTI, the investigational MK-8507, in combination with islatravir. MK-8507 has the potential to be used weekly instead of daily. Waters said she suspects that this trial is just a proof of concept of islatravir in combination with an NNRTI. Merck has signed an agreement with Gilead Sciences to co-develop islatravir with long-acting lenacapravir. Additionally, the two-drug combination of dolutegravir and lamivudine has been very successful.

"I'd be surprised if they developed islatravir/doravirine as a usable combo," she said. "It's just too soon to say. My personal view is that people are a bit too overoptimistic about it."

The study was funded by Merck. Molina has received grants from Gilead Sciences, Merck, ViiV Healthcare, and Sanofi. Waters has received speaker or advisory fees during the past 2 years from Gilead Sciences, ViiV Healthcare, Merck, Janssen, Theratech, Sipla, and Mylan.

International AIDS Society (IAS) Conference 2021: Abstract 2498. Presented July 14, 2021.

Heather Boerner is a science and medical reporter based in Pittsburgh, PA and can be found on Twitter at @HeatherBoerner. Her book, Positively Negative: Love, Sex, and Science's Surprising Victory Over HIV, came out in 2014.

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