GABAPENTIN NDA FILING PLANNED BY W-L FOR LATE 1991 AS ADD-ON ANTICONVULSANT; FOSPHENYTOIN AS NEUROPROTECTIVE AGENT FOR STROKE IN DEVELOPMENT

The NDA filing for gabapentin (CI-945) as an adjunct anticonvulsant treatment is scheduled for the third quarter of 1991, Warner-Lambert Pharmaceutical R&D Chairman Ron Cresswell, PhD, told a drug R&D update meeting for securities analysts in Ann Arbor, Mich. Nov. 6-7. The company plans "near simultaneous" registration filings in other countries, Cresswell said. Warner-Lambert will market gabapentin under the tradename Neurontin. Pharmacokinetic studies of gabapentin in humans have shown that the drug is "not metabolized and does not bond to plasma proteins," results in no hepatic problems and has "no interactions" with first-line epilepsy therapies such as phenytoin (Warner-Lambert's Dilantin), carbamazepine, valproate or phenobarbital, VP-Drug Development Fred Hershenson, PhD, reported. Gabapentin also shows no variation in effectiveness when taken with food and "no changes" in effectiveness in patients of different ages, Hershenson said. The gabapentin NDA submission will include data from three pivotal trials with more than 2,000 patients exposed to the drug worldwide. The double-blind, placebo-controlled studies were performed on patients refractory to first-line epilepsy therapy, as is normal with new anti-epileptics submitted to FDA, the company noted. Gabapentin has been under study by Warner-Lambert for about five years. The drug has been studied against placebo at doses of 300 mg/day, 600 mg/day, 900 mg/day, 1,200 mg/day and 1,800 mg/day. In the U.S. trial, which included more than 270 patients, the 600 mg/day dosage regimen showed the "best results," Hershenson reported. In two other trials, which included 225 and 126 patients, respectively, more patients had a reduction in seizures of 75% or greater with the 1,200 mg/day dosage regimen, Hershenson indicated. Somnolence and fatigue were the most frequently reported adverse reactions. Warner-Lambert Senior Director, Clinical Development-CNS Jan Wallace, MD, noted that these adverse effects were usually overcome after two to three weeks of treatment. A new candidate for human clinicals is the prodrug fosphenytoin for the mitigation of neural damage from stroke. Fosphenytoin was recently licensed by Warner-Lambert from DuPont. Given to animals one-half hour after stroke is induced, fosphenytoin produced a 40% reduction in brain damage and improved motor coordination after stroke, Frank Marcoux, PhD, director of Warner-Lambert's neurological disorders section, told the securities analysts. Marcoux said that fosphenytoin appears to block the toxic overload of calcium in neurons (hypoxia). The prodrug could potentially be used in humans on a "soonest possible" basis after stroke as a neuroprotective agent to help protect the "resavable portion" of the brain around the stroke-injured area, Marcoux said. The company says it views fosphenytoin as a short-term acute therapy for stroke. Clinicals are planned to begin next year using the prodrug in statis epilepticus and for use during neurosurgery. Asked during Q&A why the NDA filing for gabapentin is not set until the latter half of 1991, Hershenson said that because gabapentin has been under study for five years, "there is a lot of data" to prepare. He also noted that the same team that is working on the gabapentin filing is concurrently working on the drug dossier for Cognex (tacrine) (see next story), as well as on the development of fosphenytoin. Warner-Lambert President Mel Goodes used his introductory remarks to note that the company plans to spend an additional$100 mil. on the Ann Arbor facility to add two new office/lab buildings and the capital equipment for those buildings. By 1994, the expansion program at the worldwide R&D facility will have added 233,000 new square feet. Warner-Lambert's goal, he said "is to become a top tier" pharmaceutical firm.