Gabapentin enacarbil (Horizant in USA, Regnite in Japan), is a prodrug of gabapentin, an antiepileptic drug (AED). It was designed for increased oral bioavailability over gabapentin and to be transported through two high capacity transporters in the intestine, sodium-dependent multivitamin transporter (SMVT) and MCT1. It was shown that the prodrug is a substrate for both MCT1 and SMVT. The oral bioavailability of gabapentin following the administration of its prodrug was found to be 84.2% compared with 25.4% after a similar oral dose of gabapentin. Discovered and developed by XenoPort, gabapentin enacarbil was approved in the United States in 2011 for the treatment of moderate-to-severe primary restless legs syndrome (RLS) in adults and in June 2012 for the management of postherpetic neuralgia (PHN) in adults. Therapeutic effects of gabapentin enacarbil in RLS and PHN are attributable to gabapentin. The precise mechanism by which gabapentin is efficacious in RLS and PHN is unknown. In vitro studies have shown that gabapentin binds with high affinity to certain parts of voltage-activated calcium channels in the central nervous system. However, the relationship of this binding to the therapeutic effects of gabapentin enacarbil in RLS and PHN is unknown. The most common adverse reactions for adult patients with moderate-to-severe primary RLS and PHN receiving Horizant were somnolence/sedation, dizziness, headache, nausea and fatigue.