New Once-a-Month Pill Could Help Prevent HIV

Merck has announced an early global access plan for Alimatravir, an experimental once-monthly pill being developed to prevent HIV.

Known as MSD outside the United States and Canada, the pharmaceutical company aims to make the drug available quickly and affordably in low- and middle-income countries if it receives regulatory approval.

Alimatravir, also known as MK-8527, is being tested as an oral pre-exposure prophylaxis, or PrEP, for HIV-1 prevention. Unlike existing oral PrEP medicines that are generally taken every day, alimatravir is designed to be taken only once a month.

The drug is currently being evaluated in two major clinical trials.

The EXPrESSIVE-10 trial, being conducted in collaboration with the Gates Foundation, is studying its safety and effectiveness among women and adolescent girls in sub-Saharan Africa.

Meanwhile, the EXPrESSIVE-11 trial is enrolling people considered likely to be exposed to HIV across 16 countries.

Early research suggests that Alimatravir may begin working within one hour of being taken and could maintain protection for an entire month.

Researchers also believe the drug may provide a “cushion of forgiveness,” as its levels could remain high enough to prevent HIV for around one additional week if a monthly dose is taken late.

Even before the trial results are available, Merck has signed royalty-free licensing agreements with seven generic drug manufacturers. These companies would be allowed to produce and sell alimatravir in 129 low- and lower-middle-income countries.

The manufacturers include three companies based in sub-Saharan Africa and four in India. According to Merck, this is the first time African manufacturers have been included from the beginning of such an access initiative.

The move could be significant for regions carrying the highest burden of HIV. An estimated 40.9 million people were living with HIV worldwide in 2025, with more than half of them in sub-Saharan Africa.

A once-monthly pill could make HIV prevention easier for people who find it difficult to follow a daily medication schedule, while also improving access in countries with limited healthcare resources.

Results from the clinical trials are expected in the second half of next year. Merck is already expanding production so generic manufacturers can begin supplying the drug quickly if it is approved.

Alimatravir works by blocking reverse transcriptase, an enzyme HIV uses to copy its genetic material. It prevents the enzyme from moving along the viral DNA, causing immediate chain termination, while also creating structural changes that can lead to delayed chain termination.