GlaxoSmithKline and XenoPort have withdrawn their New Drug Application for their restless leg syndrome drug Solzira (gabapentin enacarbil).

The move follows a US Food and Drug Administration request that the data in a single study be reformatted. GSK will now also conduct a review of other trial data sets taking this input into account and the firm noted that the withdrawal does not relate to the content of the filing.

While GSK plans to resubmit the NDA as quickly as possible, the delay means XenoPort will have to wait for its milestone payment of $23 million in the aggregate from GSK and Astellas Pharma and will hinge on an approval by the FDA. Reuters reported that XenoPort’s shares were down to a 52-week low on the back of the news.

Solzira is a new chemical entity designed to improve upon the pharmacokinetics of gabapentin, the active pharmaceutical ingredient in Pfizer’s blockbuster epilepsy drug Neurontin, which has now gone off patent.

The extended release formulation takes advantage of high-capacity transport mechanisms in the gastrointestinal tract to improve absorption.

Earlier this year, the companies reported encouraging results from the last Phase III clinical trial of the drug that showed the drug is able to induce statistically significant improvements in the symptoms of the condition compared with a placebo. The drug is also in trials as a treatment for neuropathic pain.

Earlier this year, Pfizer’s Neurontin, along with several other epilepsy treatments were noted by the FDA as being linked to an increased risk of suicidality. US regulators rejected the proposal that the drugs should have a blackbox warning.