General Information

Horizant is an extended-release formulation of gabapentin enacarbil, a prodrug of gabapentin. The precise mechanism by which gabapentin is efficacious in RLS is unknown. Gabapentin is structurally related to the neurotransmitter gamma-aminobutyric acid (GABA) but has no effect on GABA binding, uptake, or degradation.

Horizant is specifically indicated for the treatment of moderate-to-severe primary Restless Legs Syndrome (RLS) in adults.

Horizant is supplied as an extended release tablet for oral administration. The recommended dosage is 600 mg once daily taken with food at about 5 PM.

Clinical Results

FDA Approval
The FDA approval of Horizant was based on two 12-week clinical studies in approximately 400 adults with RLS. The subjects were required to have a total score of ≥15 on the International Restless Legs Syndrome (IRLS) Rating Scale at baseline. In Study 1 the subjects received the 1,200mg of Horizant or placebo taken once daily at about 5 PM with food. In Study 2 the subjects received 600 mg of Horizant, 1,200 mg of Horizant or placebo taken once daily at about 5 PM with food. Efficacy was evaluated using the IRLS Rating Scale and Clinical Global Impression of Improvement (CGI-I) score. Statistically significant differences (P<0.05) between the treatment groups receiving 600 and 1,200 mg of Horizant and the group receiving placebo were observed at Week 12 for both the mean change from baseline in the IRLS Scale total score and the proportion of responders (much improved) or (very much improved) on the CGI-I Scale.

Mechanism of Action

Literature References

Ellenbogen AL, Thein SG, Winslow DH, Becker PM, Tolson JM, Lassauzet ML, Chen D A 52-week study of gabapentin enacarbil in restless legs syndrome. Clinical Neuropharmacology 2011 Jan-Feb;34(1):8-16

Bogan RK, Bornemann MA, Kushida CA, Trân PV, Barrett RW; XP060 Study Group Long-term maintenance treatment of restless legs syndrome with gabapentin enacarbil: a randomized controlled study. Mayo Clinic Proceedings 2010 Jun;85(6):512-21

Walters AS, Ondo WG, Kushida CA, Becker PM, Ellenbogen AL, Canafax DM, Barrett RW; XP045 Study Group. Gabapentin enacarbil in restless legs syndrome: a phase 2b, 2-week, randomized, double-blind, placebo-controlled trial. Clinical Neuropharmacology 2009 Nov-Dec;32(6):311-20

Cundy KC, Sastry S, Luo W, Zou J, Moors TL, Canafax DM Clinical pharmacokinetics of XP13512, a novel transported prodrug of gabapentin. Journal of Clinical Pharmacology 2008 Dec;48(12):1378-88