Gilead Sciences and MSD are advancing their once-weekly HIV treatment regimen to Phase II trials, following promising results from a 48-week study.

The treatment combines MSD’s islatravir, an experimental nucleoside reverse transcriptase inhibitor, with Gilead’s lenacapavir, marketed as Sunlenca for use in combination with other antiretroviral drugs to treat people with multidrug-resistant HIV infection. In contrast to currently available daily HIV medications, such as Gilead’s Biktarvy (bictegravir 50mg/emtricitabine 200mg/tenofovir alafenamide 25mg), this new option could offer a long-acting alternative for people living with HIV.

In the Phase II trial (NCT05052996), 104 virologically suppressed adults on Biktarvy were randomly assigned to either continue their daily regimen or switch to the once-weekly islatravir/lenacapavir combination. At the 24-week mark, 94.2% of patients on the experimental treatment maintained viral loads below 50 copies m/L – a key threshold for HIV suppression – matching the Biktarvy group.

By week 48, the new regimen continued to demonstrate non-inferior efficacy, with 94.2% of participants achieving sustained viral suppression, compared to 92.4% of those who remained on Biktarvy.

These results suggest that the once-weekly combination could provide a more convenient option for patients, potentially reducing the burden of daily medication. Currently, the only long-acting HIV treatment available in the US is Viiv Healthcare’s Cabenuva, which is administered as a monthly or bi-monthly injection. This could make Gilead and MSD’s new pill an attractive alternative to those seeking a less frequent oral regimen.

Biktarvy is approved as a once-daily pill to treat patients living with certain types of HIV. The drug generated $11.9bn in global sales in 2023, as per Gilead’s financials. According to GlobalData’s Pharma Intelligence Center, Biktarvy will generate $15.3bn in sales in 2030.

GlobalData is the parent company of Clinical Trials Arena.

In the announcement accompanying the results, Elizabeth Rhee, vice president of global clinical development of Merck Research Laboratories said: “Daily single-tablet regimens have helped to transform HIV care but can be challenging for some people to maintain. Novel HIV treatment options that allow for less frequent oral dosing have the potential to help support adherence, and address stigma faced by some individuals taking daily oral therapy.”

MSD previously tried to develop a higher dose of islatravir, however it had to pause development after it led to a drop in counts of lymphocytes and CD4+ T cells in clinical trials in 2021. In MSD and Gilead’s Phase II study, there were no differences in immune cell count changes between the Biktarvy and experimental groups. Additionally, no participants discontinued because of a decrease in CD4+ T-cell or lymphocyte counts. Encouraged by these results, Gilead and MSD are now advancing the treatment in Phase III trials.