Merck Presents Results from Phase 1 Trial Evaluating Investigational Islatravir Subdermal Implant for the Prevention of HIV-1 Infection at CROI 2021


March 8, 2021 11:40 am ET

Company to Proceed with Phase 2 Development Program for Islatravir Subdermal Implant

KENILWORTH, N.J.--(BUSINESS WIRE)-- Merck (NYSE: MRK), known as MSD outside the United States and Canada, today announced results from a Phase 1 study evaluating the safety, tolerability and pharmacokinetics (PK) of the company’s investigational subdermal drug-eluting implant with potential for extended administration of islatravir for pre-exposure prophylaxis (PrEP) of HIV-1 infection. Islatravir is an investigational nucleoside reverse transcriptase translocation inhibitor (NRTTI) currently being evaluated across a variety of doses, formulations and frequencies for both the treatment of HIV-1 infection in combination with other antiretroviral agents and for the prevention of HIV-1 infection as a single agent. Study results, presented as a late-breaking oral presentation [Presentation 88] at the 2021 Conference on Retroviruses and Opportunistic Infections (CROI 2021), demonstrate that the implant achieved active drug concentrations above the pre-specified PK threshold at 12 weeks across the three doses of islatravir studied (48 mg, 52 mg and 56 mg), and is projected to provide drug concentrations likely above threshold for one year at the 56 mg dose. Based on these findings, Merck plans to initiate a Phase 2 trial to further explore the potential of a subdermal implant containing islatravir as a long-acting option for PrEP for up to 12 months.

“We are delighted to share our early data at CROI 2021 supporting the potential for a once-yearly dosing regimen for islatravir using a subdermal implant,” said Dr. Joan Butterton, vice president, global clinical development, infectious diseases, Merck Research Laboratories. “We know that PrEP can have a positive impact in curbing the spread of HIV and are looking forward to evaluating our implant further with the goal of developing new long-term options for HIV prevention.”

Phase 1 Implant Study Results for Investigational Anti-HIV agent Islatravir

The Phase 1 double-blind, placebo-controlled trial evaluated the safety, tolerability and PK of islatravir administered using a drug-eluting implant placed subdermally in healthy participants. People in the study received an implant containing islatravir at doses of either 48 mg (n=8), 52 mg (n=8), 56 mg (n=8) or placebo (n=12; 4 in each dose level). After 12 weeks, the implant was removed, and participants were evaluated for an additional eight weeks.

At 12 weeks, all three doses resulted in mean islatravir triphosphate (the active form of islatravir) concentrations above the target PK threshold (0.05 pmol/106 cells), the lowest level of islatravir triphosphate projected to have an antiviral effect as monotherapy in humans based on Phase 1 and Phase 2 data. The top two doses (52 mg and 56 mg) maintained islatravir triphosphate levels above the PK threshold in all individuals from implant insertion until the end of the study. The results of this study, along with previous assessments of islatravir implants, provide evidence for the potential of implants to generate levels of islatravir triphosphate projected to provide drug concentrations likely above the target PK threshold for at least one year.

In this study, 67% of (n=24/36) participants reported at least one implant site adverse event (AE). All AEs were mild or moderate in severity and there were no discontinuations due to an AE. Common AEs included erythema (3/12; 4/8; 2/8; 4/8), tenderness/pain (4/12; 2/8; 4/8; 4/8), pruritus (3/12; 5/8; 2/8; 6/8), and induration (2/12; 4/8; 4/8; 4/8) for the placebo, 48 mg, 52 mg, and 56 mg groups, respectively. The most common AE not related to the implant site was headache, affecting six individuals overall. There was no clear relationship between dose and implant site AE frequency or severity.

About Islatravir (MK-8591)

Islatravir (formerly MK-8591) is Merck’s investigational nucleoside reverse transcriptase translocation inhibitor (NRTTI) under evaluation in clinical trials for the treatment of HIV-1 infection in combination with other antiretrovirals, including the ILLUMINATE clinical trials program for once-daily treatment. Islatravir is also being studied for pre-exposure prophylaxis (PrEP) of HIV-1 infection as a single agent across a variety of formulations, including the IMPOWER clinical trials evaluating an oral once-monthly regimen.

Our Commitment to HIV

For more than 35 years, Merck has been committed to scientific research and discovery in HIV, and we continue to be driven by the conviction that more medical advances are still to come. Our focus is on pursuing research that addresses unmet medical needs and helps people living with HIV and their communities. We remain committed to working hand-in-hand with our partners in the global HIV community to address the complex challenges that hinder continued progress toward ending the epidemic.

Our Commitment to Infectious Diseases

For more than 100 years, Merck has contributed to the discovery and development of novel medicines and vaccines to combat infectious diseases. In addition to a combined portfolio of vaccines and antibacterial, antiviral and antifungal medicines, Merck has multiple programs that span discovery through late-stage development. To learn more about Merck’s infectious diseases pipeline, visit

About Merck

For 130 years, Merck, known as MSD outside of the United States and Canada, has been inventing for life, bringing forward medicines and vaccines for many of the world’s most challenging diseases in pursuit of our mission to save and improve lives. We demonstrate our commitment to patients and population health by increasing access to health care through far-reaching policies, programs and partnerships. Today, Merck continues to be at the forefront of research to prevent and treat diseases that threaten people and animals – including cancer, infectious diseases such as HIV and Ebola, and emerging animal diseases – as we aspire to be the premier research-intensive biopharmaceutical company in the world. For more information, visit and connect with us on Twitter, Facebook, Instagram, YouTube and LinkedIn.

Forward-Looking Statement of Merck & Co., Inc., Kenilworth, N.J., USA

This news release of Merck & Co., Inc., Kenilworth, N.J., USA (the “company”) includes “forward-looking statements” within the meaning of the safe harbor provisions of the U.S. Private Securities Litigation Reform Act of 1995. These statements are based upon the current beliefs and expectations of the company’s management and are subject to significant risks and uncertainties. There can be no guarantees with respect to pipeline products that the products will receive the necessary regulatory approvals or that they will prove to be commercially successful. If underlying assumptions prove inaccurate or risks or uncertainties materialize, actual results may differ materially from those set forth in the forward-looking statements.

Risks and uncertainties include but are not limited to, general industry conditions and competition; general economic factors, including interest rate and currency exchange rate fluctuations; the impact of the global outbreak of novel coronavirus disease (COVID-19); the impact of pharmaceutical industry regulation and health care legislation in the United States and internationally; global trends toward health care cost containment; technological advances, new products and patents attained by competitors; challenges inherent in new product development, including obtaining regulatory approval; the company’s ability to accurately predict future market conditions; manufacturing difficulties or delays; financial instability of international economies and sovereign risk; dependence on the effectiveness of the company’s patents and other protections for innovative products; and the exposure to litigation, including patent litigation, and/or regulatory actions.

The company undertakes no obligation to publicly update any forward-looking statement, whether as a result of new information, future events or otherwise. Additional factors that could cause results to differ materially from those described in the forward-looking statements can be found in the company’s 2020 Annual Report on Form 10-K and the company’s other filings with the Securities and Exchange Commission (SEC) available at the SEC’s Internet site (


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Source: Merck & Co., Inc.

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