Phenytoin: Repurposing an Old Molecule and Patent Strategies for Neuropathic Pain

Phenytoin was introduced in the clinic in 1938, and due to its broad mechanism of action it has become a clear prototype of a repurposed or repositioned drug in a variety of indications, from bipolar disorders up to wound healing. Some years ago, we identified phenytoin as a co-analgesic with optimal properties to put into a topical formulation for the treatment of peripheral neuropathic pain. Phenytoin is the archetype of a sodium channel blocking drug and the main target for its efficacy as a neuropathic analgesic resides in the epidermis: the nociceptor. The development however of an old drug in a new off-label indication can only be attractive in case of a well-balanced patent strategy.