Funapide (also known as TV 45070; XEN 402) is a small molecule blocker of the voltage-gated sodium channels Nav1.7 (SCN9A) and Nav1.8. Funapide was developed as a potential treatment of pain conditions, including osteoarthritis, neuropathic pain, postherpetic neuralgia, and erythromelalgia, as well as dental pain. In April 2013, the US FDA granted orphan drug designation to funapide for the treatment of pain associated with erythromelalgia (EM). EM is a rare autosomal dominant condition characterized by debilitating spontaneous or easily evoked attacks of symmetrical burning pain in the feet and hands, typically associated with elevated skin temperature and erythema (redness of the skin). Funapide also was involved in phase II clinical trials in patients with post herpetic neuralgia and in participants with primary osteoarthritis (OA) affecting a single knee. On March 7, 2018, Teva Pharmaceutical and Xenon Pharmaceuticals entered into a mutual agreement to terminate the collaborative development and license agreement they entered into in 2012 for the pain drug funapide. The reason was that the top line results of funapide phase 2 study in post-herpetic neuralgia patients failed to meet the primary or secondary endpoints.