MK-5661

MK-5661 is a selective small molecule inhibitor of the voltage-gated sodium channel Nav1.7 (SCN9A), developed by Merck Sharp & Dohme for the treatment of chronic pain conditions, including postherpetic neuralgia. Nav1.7 is highly expressed in peripheral nociceptive neurons and plays a critical role in the generation and conduction of pain signals. By selectively targeting Nav1.7 over other sodium channel isoforms, such as Nav1.5 in the heart, MK-5661 was designed to provide effective analgesia while minimizing cardiovascular and central nervous system side effects. Clinical development of MK-5661 reached Phase 2 trials for postherpetic neuralgia but was subsequently terminated by the developer.