By Ed Susman
Pharmacokinetic data indicated that an implant containing 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), the 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, senior scientist at Merck in Kenilworth, New Jersey.
The highest dose, 56 mg, was projected to produce adequate blood levels of islatravir for nearly all people for at least 52 weeks, he said in his oral presentation at the virtual Conference on Retroviruses and Opportunistic Infections (CROI) .
“Next-generation islatravir implants provide drug release that is expected to be sufficient for HIV prophylaxis for at least one year,” Matthews said. “Islatravir-releasing implants appear to be well-tolerated, and the results of this trial support further study of these implants in a larger, longer phase II trial. A PrEP implant could provide an attractive option for people who find a daily PrEP regimen challenging.”
In the study, patients were implanted with the Nexplanon applicator, which has been used for years to deliver contraceptives. The implant is coated with radioactive barium so that it can be tracked if it migrates.
The implants were placed in the upper arms of the patients and were to remain in place for 12 weeks, at which point they were removed and the patients were monitored for another 8 weeks. During that period, drug levels decreased with a half-life of approximately 8 days.
Matthews and colleagues enrolled eight people in each of the three dose groups: 48, 52, and 56 mg. An additional 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 injection site redness, tenderness and pain, and some itching.
“With PrEP, there’s no one-size-fits-all approach,” said Richard Koup, MD, a senior investigator at the National Institute of Allergy and Infectious Diseases, who moderated a press conference featuring Matthews. “The more options we have—whether it’s monoclonal antibodies, long-acting antiretrovirals, or implantable agents—the better. This will always be a challenge for some individuals or populations with one of these modalities.”
Co-moderator Sharon Hillier, PhD, of the University of Pittsburgh School of Medicine, told MedPage Today: “Not everyone would want an implant, but many women find that using an implant is an excellent form of contraception. It’s not that islatravir will be the answer, but it will be another approach that some people may use.”
Reference source: Matthews R, et al "NEXT GENERATION ISLATRAVIR IMPLANTS TARGETED TO PROVIDE ANNUAL HIV PROPHYLAXIS" CROI 2021; Abstract 88.