Islatravir (MK-8591) is an investigational pharmaceutical compound primarily studied for the treatment and prevention of HIV infections. It acts as a nucleoside reverse transcriptase translocation inhibitor (NRTTI), a subclass of nucleoside reverse transcriptase inhibitors (NRTIs), by blocking the reverse transcriptase enzyme that HIV uses to replicate its genetic material. This mechanism positions it as a promising candidate for both therapeutic and prophylactic applications. Clinical trials have demonstrated its potential as a long-acting oral medication, which could reduce dosing frequency compared to current antiretroviral therapies. It is also being evaluated in combinations with other antiretrovirals to improve efficacy and minimize resistance development. Furthermore, Islatravir is under investigation for pre-exposure prophylaxis (PrEP) in high-risk populations, with its long-acting properties potentially providing a more convenient and adherent option for HIV prevention. Research is ongoing for extended-release formulations, including implants and injectables, to enhance usability.