Arm Implant to Prevent HIV in Reach

Heather Boerner

July 24, 2019

MEXICO CITY — A whip-thin length of polymer loaded with islatravir, Merck's investigational HIV prevention drug, and implanted into the arm is being investigated as a future option for people who have a hard time taking pills.

The drug — previously referred to at MK-8591 or, for prevention, EFdA — has been a hot topic at HIV conferences in recent years, even though all data presented have come from preclinical nonhuman primate studies.

But in a packed room at the end of a long conference day here at the International AIDS Society (IAS) 2019 Conference on HIV Science, Randolph Matthews, MD, PhD, a senior scientist at Merck, presented 12-week data from a phase 1 pilot study of the long-acting HIV pre-exposure prophylaxis (PrEP).

For the first time, we have demonstrated the potential for long-acting implant formulations of islatravir that can deliver medications for at least 1 year, Matthews told Medscape Medical News. "It could represent a meaningful option for many people throughout the world, particularly those with adherence challenges."

One of the studies presented at the conference showed that young African women would initiate oral PrEP but most discontinued after 3 months. And a study of same-day PrEP uptake by gay and bisexual men and transgender women in Latin America showed that only 56% of trans women were still taking PrEP a few weeks after initiation.

So it is understandable that people flocked to see how 16 people fared in a randomized, double-blind, placebo-controlled trial of a longer-acting approach. And they fared pretty well.

Long-Acting Implant

The 16 participants were randomized to receive implantable islatravir — either 54 mg or 62 mg — or placebo, and were followed for 12 weeks. Blood tests were used to assess whether the drug concentration exceeded the goal of 0.05 pmol/106. The implants were then removed and participants were followed for another 4 weeks to see how long the drug remained in their system.

In the 54 mg group, drug levels remained above the threshold until about a week after removal. In the 62 mg group, drug levels were consistently higher and did not drop below the threshold until 3 weeks after removal.

Matthews and his colleagues used modeling to determine how long the drug might last in a person's system with continuous use at each dosage.

"The high-dose implant would still be above the target level for at least 1 year," Matthews reported.

But a 12-week pilot isn't the same as a 12-month trial powered to detect effectiveness, and drug levels don't equal HIV prevention — and audience members pointed that out.

Drug Levels Don't Equal Prevention

Still, "this is the first time we've ever seen an HIV drug delivered in an implant," said Roy Gulick, MD, from the Weill Cornell Medical Center in New York City.

And if it does work, "what a fantastic thing," he told Medscape Medical News. "The current problem with PrEP is that people don't want to take one pill a day."

"Of course, we don't know if it works yet," he added.

"This is one of the most exciting and challenging times in HIV research," said Mitchell Warren, executive director of AVAC, a global advocacy group for the prevention of HIV.

Merck is planning a phase 2 study to test the drug and delivery system in a larger, more diverse cohort. Of the 16 trial participants, two were women, none were transgender, and all were white.

The results presented this week provide a glimpse of a possible, promising future.

Warren said he looks at the field now and he has hope despite barriers to care and the difficulty engaging people most at risk for HIV.

Final data from the HOPE open-label extension trial of an HIV prevention vaginal ring (NCT02858037), presented at the IAS conference, previous data from the LATTE trial of a long-acting injection to prevent HIV, and other data on a vaccine and potential monthly treatment for HIV could change what HIV prevention looks at in a few years.

"No one method will ever be 'the method'," Warren said. "But the collection of them all is critical to a sustainable end to the epidemic. We have a long way to go, but the results presented this week provide a glimpse of a possible, promising future."

The islatravir study was funded by Merck. Warren and Gulick have disclosed no relevant financial relationships. Matthews is an employee of Merck.

International AIDS Society (IAS) 2019 Conference on HIV Science: Abstract TUAC0401LB. Presented July 23, 2019.

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