* Pfizer says placebo group had higher than expected response
* Trial is first of three testing once-daily formulation
Nov 16 (Reuters) - Pfizer Inc said on Friday a late-stage trial of a once-a-day formulation of its drug pregabalin did not significantly reduce the frequency of some types of seizures in patients with epilepsy.
Pfizer's biggest product, sold under the brand name Lyrica, is used to treat epilepsy when given several times a day in combination with other drugs. The drug, with $4 billion in annual sales, is more widely used to treat nerve pain.
Pfizer said the lack of a statistically significant improvement may have been due to a higher-than-expected response among patients taking the placebo.
The study was the first of three trials testing the drug as a once-a-day therapy. The company is also testing it in patients with fibromyalgia and some types of nerve pain, for which it is also approved in its immediate-release formulation.