A drug for Parkinson's in development at GlaxoSmithKline and Impax Pharmaceuticals has outperformed a mainstay therapy for the disease in a second Phase III trial.

Top-line results from the ASCEND-PD Phase III trial of IPX066 versus carbidopa-levodopa plus entacapone (CLE) in patients with advanced Parkinson's showed that GSK and Impax' drug provided greater control of the debilitating motor symptoms of the disease.

IPX066 is an extended-release formulation of carbidopa-levodopa which is designed to maintain blood levels of the drugs more consistently over time than currently-available formulations.

The primary endpoint of the trial was the percentage of 'off time' during waking hours as measured by patient diaries. Off time refers to the periods when a patient's medication has worn off and the motor symptoms of Parkinson's re-establish themselves.

ASCEND-PD showed that patients on IPX066 cut their percentage off-time by around a third (33.5%) compared to baseline levels, while those on CLE showed a 10% decrease.

That equated to an 84-minute improvement in off time over CLE therapy. Moreover, the increase in on time - with symptoms managed effectively - was achieved without any increase in side effects such as dyskinesias.

The results are in line with an earlier Phase III study - ADVANCE-PD - which was reported in February, and GSK and Impax say they can now press ahead with filing for approval of IPX066 in the USA later this year and in the EU in early 2012. A third Phase III trial called APEX-PD in early Parkinson's patients was reported in April.

GSK partnered with Impax on IPX066 in December 2010 in a deal involving $11.5 million in upfront payments and $175 million in development and commercialisation milestones. Under the terms of the deal GSK has rights to market the drug worldwide, except in the USA and Taiwan.