Regulators in the USA have told GlaxoSmithKline and partner Xenoport that they want additional preclinical data on Horizant, a potential treatment for restless legs syndrome.

In February this year, GSK received a complete response letter from the US Food and Drug Administration about Horizant (gabapentin enacarbil) extended-release tablets for the treatment of moderate-to-severe primary RLS. In the letter, the agency said the firms’ New Drug Application “provides substantial evidence of effectiveness” and the FDA “had not identified a clinical safety concern that would prevent approval”.

However, a preclinical signal of pancreatic acinar cell tumours in rats was “determined to be of sufficient concern to preclude approval of the Horizant NDA” in its current form. Therefore, a week ago, XenoPort and GSK conducted an end-of-review meeting with the agency where the latter “suggested additional preclinical data and data analyses that may be useful in the evaluation of the resubmission”.

The companies are evaluating this additional work and noted that no new clinical trials “are expected at this time”. XenoPort expects the file to be resubmitted in the second half of 2010.

Orlistat label updated to include liver risk
Meantime, the FDA has approved label changes for the weight loss drug orlistat, marketed under prescription by Roche as Xenical and sold over the counter by GSK as Alli, to include safety information about cases of severe liver injury “that have been reported rarely with the use of this medication”.

The label update is based on a review which identified 12 reports of severe liver injury among people taking Xenical and one report in Alli users between April 1999 and August 2009. This is out of an estimated 40 million people worldwide who have taken the drug.