Merck Reports Positive Phase 1 Results for Once-Yearly Islatravir Implant as HIV Pre-Exposure Prophylaxis

Today, MSD announced that its investigational nucleoside reverse transcriptase translocation inhibitor (NRTTI) islatravir (also known as MK-8591) achieved positive results in a Phase 1 clinical trial. Administered via subcutaneous sustained-release implants at three different doses, islatravir maintained drug concentrations above the predefined pharmacokinetic (PK) threshold for 12 weeks post-implantation. The 56-mg dose of islatravir is projected to sustain drug concentrations above this threshold for more than one year. Based on these positive findings, MSD will initiate a Phase 2 clinical trial to further explore the potential of the subcutaneous islatravir implant as a long-acting pre-exposure prophylaxis (PrEP) regimen, which could provide up to 12 months of protective efficacy with a single administration.

With the advent of “cocktail therapy,” HIV/AIDS has transformed from a dreaded, life-threatening disease into a chronic condition manageable with medication. However, the incidence of HIV remains high in certain countries. Pre-exposure prophylaxis (PrEP) aims to provide preventive treatment to individuals at risk of HIV-1 infection, thereby reducing their likelihood of contracting the virus. Nevertheless, current PrEP regimens require daily medication adherence among high-risk populations; poor compliance significantly increases their risk of infection.

Islatravir is an innovative nucleoside reverse transcriptase translocation inhibitor (NRTTI) developed by Merck & Co., Inc. Preclinical studies have demonstrated that it inhibits HIV reverse transcriptase function through multiple mechanisms, with a mode of action distinct from currently approved anti-HIV therapies and traditional nucleoside reverse transcriptase inhibitors (NRTIs). Merck & Co., Inc. is currently evaluating its efficacy in multiple clinical trials, both as monotherapy for pre-exposure prophylaxis (PrEP) and in combination with other antiviral agents for the treatment of HIV infection.

In this double-blind, placebo-controlled Phase 1 clinical trial, 24 healthy participants received an implant containing varying doses of islatravir in the upper arm. The implant slowly released the drug in vivo, thereby maintaining therapeutic drug concentrations over an extended period. Twelve weeks after implantation, the implants were removed, and the participants subsequently underwent an 8-week evaluation period.

Trial results showed that implants with three different doses all maintained islatravir concentrations above the level required for antiviral efficacy within 12 weeks. For the higher doses (52 mg and 56 mg), islatravir concentrations remained above the threshold after implant removal until the end of the study. Based on these trial results and previous evaluations of islatravir implants, researchers expect this delivery method to maintain drug concentrations above the target pharmacokinetic (PK) threshold for at least one year.

Note: This article is intended to introduce medical and health research and does not constitute a recommendation for treatment plans. For guidance on treatment options, please consult a licensed healthcare provider at a reputable hospital.

References:

[1] Merck Presents Results from Phase 1 Trial Evaluating Investigational Islatravir Subdermal Implant for the Prevention of HIV-1 Infection at CROI 2021. Retrieved March 8, 2021, from https://www.businesswire.com/news/home/20210308005050/en

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