Mid-Study Peek at Merck's Once-A-Month HIV Preventative Shows Promise

Merck_Smith Collection/Gado/Getty Images

Smith Collection/Gado/Getty Images

Merck & Co. announced data from its Phase IIa trial of islatravir for pre-exposure prophylaxis (PrEP) of HIV-1 infection in adults who are at low risk of contracting HIV. The drug is a nucleoside reverse transcriptase translocation inhibitor, with the results presented at the virtual 11th International AIDS Society Conference on HIV Science (IAS 2021). 

The Phase IIa study is still ongoing. Participants were randomized 2:2:1 to one of three once-monthly cohorts, islatravir 60 mg, islatravir 120 mg or placebo. 

The drug is an oral medication, and they received it once a month over 24 weeks with the data blinded. Then they were followed by a 12-week follow-up where the data was also blinded, then a 32-week follow-up that was unblinded in the islatravir groups. The study plans to measure data through week 68.

Of the 242 participants in the 24-week portion, 92% completed dosing and 8% discontinued before week 24. Less than 1% quit as the result of adverse side effects. The breakdown of the participants was 67.4% female, 52.9% white, 41.7% Black or African American, and 14.9% were Hispanic or Latino. 

In the unblinded data, patients tolerated both doses of the drug compared to placebo over 24 weeks. Most adverse events (AE) were mild, about 73.5%. The most common side effects in the islatravir group receiving 120 mg and 60 mg doses were headache, diarrhea, and nausea. Patients receiving islatravir did not report serious drug-related adverse events. 

The study participants were at low risk for HIV, and there were no confirmed HIV infections during the treatment period.

“The 24-week analysis of investigational, once-monthly oral islatravir not only builds upon the PK data we have already seen, but also provides encouraging support for the safety and tolerability profile of this HIV-1 PrEP regimen,” said Joan Butterton, vice president global clinical development, infectious diseases, Merck Research Laboratories. 

“As part of our commitment to understanding the potential for our HIV medicines in a broad range of patients, we focused on the enrollment of diverse patient populations at risk for HIV, including women, who have one of the highest unmet needs in HIV prevention.”

In March 2021, Merck and Gilead Sciences inked a deal to co-develop and co-commercialize long-acting therapies for HIV that combine Gilead’s lenacapavir and Merck’s islatravir into a two-drug regimen. Gilead’s drug is an experimental capsid inhibitor. 

Both drugs are potential first-in-class therapeutics, both in late-stage clinical trials. The drugs have long half-lives and have shown activity in low dosages.

The studies are expected to start in the second half of this year. The two companies are splitting responsibilities, including development, commercialization, marketing costs, and future revenues.

At the time, Daniel O’Day, chairman and chief executive officer of Gilead stated, “Through this agreement with Merck, Gilead is reinforcing its long-term role in transforming HIV care. Our work in HIV over the past decades has been shaped by listening to people living with HIV and the physicians who treat them. Now we are taking the same approach with long-acting therapies, combining the most advanced science from both companies to accelerate progress.”

Beyond this specific deal, Gilead has the option to license some of Merck’s investigational oral integrate inhibitors as potential combination therapies with lenacapavir. On the other side, Merck has the option to license specific Gilead oral integrate inhibitors for combination therapies with islatravir. Those options can be triggered after completing the first Phase I trial of the integrate inhibitor in question.

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