GSK Restless Legs Syndrome drug approved

GlaxoSmithKline (GSK) and XenoPort have won marketing approval from the US Food and Drug Administration (FDA) for Horizant (gabapentin enacarbil), a non-dopaminergic treatment for moderate-to-severe primary Restless Legs Syndrome (RLS).

RLS is a neurological disorder characterised by an urge to move the legs that is often accompanied by uncomfortable sensations.

Horizant's approval for the condition was based on two 12-week clinical trials in adults with RLS.

The companies submitted their new drug application (NDA) for the extended-release tablets in January 2009, but were issued a complete response letter by the FDA last year declining to approve the drug at that time due to concerns about a preclinical finding of pancreatic acinar cell tumours in rats.

The drug, which was discovered and developed by XenoPort, is converted into gabapentin once it is absorbed by the body. Gabentin, marketed by Pfizer as Nerontin to control seizures in epilepsy patients, also appeared to cause cancer in rats in preclinical trials, but in that case, the FDA stated that the 'seriousness and severity of refractory epilepsy justified the potential risks'.

However, the concerns about the preclinical findings in Horizant appear to have been resolved: the FDA said that Horizant will be marketed with an approved Medication Guide to alert patients to the drug's risks, but the information in the guide will focus on the likelihood of drowsiness and dizziness that can impair a person's ability to drive or operate complex machinery when taking the drug.