Impax Labs files Gralise patent challenge

HAYWARD, Calif. — Generic drug maker Impax Labs is challenging the patent protection on a drug used to treat postherpetic neuralgia, the company said Thursday.

Impax announced that it had filed a regulatory approval application with the Food and Drug Administration for gabapentin tablets, a generic version of Depomed's Gralise, in the 300-mg and 600-mg strengths.

The application contained a Paragraph IV certification, a legal assertion that the patents covering the drug are invalid, unenforceable or won't be infringed. In response, Depomed filed a lawsuit against Impax Tuesday in the U.S. District Court for the District of New Jersey.

Gralise had sales of about $1.3 million during the three-month period ended in February, according to Wolters Kluwer Health.