Houston Methodist researchers have developed a long-acting, refillable implant that delivers HIV prevention medication for up to 20 months, according to recent research in animal models.

In a study published in the journal Science Translational Medicine, titanium implants placed just below the skin of six rhesus macaque monkeys delivered a continuous dose of experimental antiviral medication islatravir (ISL) that prevented the transmission of simian HIV in repeated exposure tests.

If the implant proves equally successful in human clinical trials, it could represent a major turning point in scientists' decades-long battle to eradicate the disease.

When taken as directed, antiretroviral medication delivered as part of a pre-exposure prophylaxis (PrEP) protocol is 99% effective at preventing sexually acquired human immunodeficiency virus.

"The key phrase is 'when taken as directed,'" said Alessandro Grattoni, Ph.D., chair of the Department of Nanomedicine at Houston Methodist Research Institute. "Many patients miss or forget to take their medications as scheduled, making it significantly less protective."

As a result, the CDC estimates that HIV transmission rates have only dropped 8% in the U.S. since 2015, when PrEP became widely available.

"Our goal was to find a fool-proof delivery mechanism that would be easier and more convenient to use for patients who have trouble adhering to a daily oral pill regimen or bi-monthly injection schedule," Grattoni said.

Experts estimate that three out of every four Americans fail to take their medicine exactly as prescribed.

"Medication non-adherence isn't unique to those at risk of HIV, but what is somewhat unique is the extremely high price these individuals might pay for one missed dose," Grattoni says. "While HIV is not the death sentence it once was, it is still a lifelong condition that requires close management and medication to stay healthy."

The implants are designed to be safe against both leaks and ruptures and have space for roughly .57 milliliters of ISL.

Within one day, researchers found that all monkeys who received implants had amassed protective levels of circulating ISL. Tests conducted throughout the 20-month study showed that circulating blood concentrations of ISL matched the desired protective levels that would have been seen had the monkeys received ISL via a weekly pill. All implanted monkeys appeared to be fully protected against simian HIV exposure via both the rectum and the vagina, with no safety or tolerance issues.

Grattoni and team are currently preparing for a human trial, which they hope to initiate within three years. If all goes well, they estimate the implant could become available for patients within the next five years.

The study was initially covered by HealthDay.

Read more about the Grattoni Lab's recent research here.