FDA rejects GSK and Xenoport's Horizant

GlaxoSmithKline (GSK) and XenoPort, have received a Complete Response letter from the US Food and Drug Administration (FDA) relating to Horizant (gabapentin enacarbil), an investigational non-dopaminergic treatment for moderate-to-severe primary Restless Legs Syndrome (RLS).

The two companies submitted a New Drug Application (NDA) for Horizant extended-release tablets, to the FDA in January 2009.

The FDA's Center of Drug Evaluation and Research issue Complete Response letters once a review is completed, but when there are questions outstanding that prevent the NDA from being approved.

In the case of Horizant, the FDA indicated that a preclinical finding of pancreatic acinar cell tumours in rats was of sufficient concern to prevent approval of Horizant for RLS at this time.

GSK and Xenoport are evaluating the Complete Response letter and will communicate their intended next steps to the FDA.

Horizant is developed from a variant of Pfizer's Nerontin (gabentin), used to control seizures in epilepsy patients. Similar preclinical findings to those for Horizant were known for gabapentin when the FDA approved its use for refractory epilepsy. However, the FDA state that the 'seriousness and severity of refractory epilepsy justified the potential risks'.

Gabapentin enacarbil is also being developed in partnership with Astellas Pharma for the potential treatment of Restless Legs Syndrome in Japan.