US regulators have delayed the approval of Requip XL, a reformulated drug for Parkinson's disease, in a blow to GlaxoSmithKline and SkyePharma.

The Food and Drug Administration deferred its decision on the drug, an extended release version of GSK's Requip also known as Ropinirole, after the company submitted additional information on the food effects of the medicine last month in response to regulators' queries.