Merck tips implant to give yearly HIV protection, plans phase 2

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A one-year implant is a viable prospect due to the potency of islatravir

A phase 1 trial has found an implantable formulation of Merck’s islatravir could protect against HIV for at least one year. Merck is now preparing to start a phase 2 study of the subdermal implant. 

A range of formulations of islatravir, a nucleoside reverse transcriptase translocation inhibitor, are in development in the prevention and treatment of HIV. Merck shared an update on its work to validate islatravir in HIV prophylaxis at the 2021 Conference on Retroviruses and Opportunistic Infections last week, offering encouragement for its hopes of providing long-term protection against the virus. 

Investigators in the phase 1 clinical trial implanted devices that eluted one of three doses of islatravir or placebo and tracked participants at low risk of HIV infection for 12 weeks. By extrapolating from the 12-week data, researchers forecast the high-dose implant will provide islatravir at concentrations above the threshold for prophylaxis for at least 52 weeks. 

The findings suggest an islatravir-eluting implant could free people from the need to take medication such as Gilead’s Descovy every day. By eliminating the risk of missed doses, Merck’s implant could tackle the adherence problem that can cause people to contract HIV despite taking pre-exposure prophylactics. 

A one-year implant is a viable prospect due to the potency of islatravir, which reduces the size of the device, and Merck’s work to optimize the release dynamics. Concentrations of islatravir delivered by all three doses of the implant stayed above the threshold for the duration of the 12-week study, with the highest dose forecast to provide the longest-lasting protection.

Increasing the dose had no clear effect on the safety and tolerability of the implants. Most subjects reported at least one implant-site adverse event such as tenderness or redness of the skin. Merck sees enough promise in the data to start gearing up for a phase 2 clinical trial,