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Pharmacokinetic data indicated that an implant that elutes islatravir, an antiretroviral agent, could protect people at-risk of contracting HIV for at least a year, positioning it as a potential form of pre-exposure prophylaxis (PrEP), researchers reported.

In a trial in which people at low risk of HIV-infection were implanted with three different doses of islatravir, blood levels of islatravir remained well above the level considered sufficient for protection against infection at week 12, according to Randolph Matthews, MD, PhD, a senior scientist at Merck in Kenilworth New Jersey.

The largest dose – 56 mg – was projected to yield adequate islatravir blood levels for almost all individuals for at least 52 weeks, he said in his oral presentation at the virtual .

This was the second virtual CROI, relegated to Zoom format due to the COVID-19 pandemic. The meeting was one of the first to go virtual in 2020 – indeed, some prospective attendees had already arrived when the in-person conference was cancelled.

"Next-generation radiopaque islatravir-eluting implants provide drug release projected to be sufficient for HIV prophylaxis for at least one year," Matthews said. "Islatravir-eluting implants appear to be well tolerated, and the results from this trial support further study of these implants in a larger, longer phase II trial. A PrEP implant could provide an attractive option for individuals in whom adherence to a daily PrEP regimen is challenging."

In the study, patients were implanted using the Nexplanon applicator that has been used for years to implant contraceptives. The implant is bathed in radioactive barium so it can be tracked in case of migration.

The implants were placed in patients' upper arms and were to remain in place for 12 weeks, at which point they were removed and patients were monitored for another 8 weeks. Over that span, drug levels dropped with a half-life of about 8 days.

Matthews and colleagues enrolled eight individuals in each of three dosage groups – 48, 52, and 56 mg. Another 12 untreated individuals served as controls. Of the 36 patients, 22 reported at least one adverse event; none were serious and no one had to discontinue treatment due to adverse events. Side effects included redness at the injection site, tenderness and pain, and some pruritus.

"With PrEP, there is no such thing as one size fits all," said Richard Koup, MD, senior investigator at the National Institute of Allergy and Infectious Diseases, who moderated a press conference where Matthews spoke. "The more opportunities that we have, whether it is monoclonal antibodies, long-acting antiretrovirals, implantable agents, the better. This is always going to be an issue for some person or some population with one of these modalities."

Co-moderator Sharon Hillier, PhD, of the University of Pittsburgh School of Medicine, told 麻豆传媒, "Not everybody would want an implant, but many women find that using an implant is an outstanding way for contraception. It is not that islatravir is going to be the answer, but it will be another approach that some people can use."