(Reuters) - Supernus Pharmaceuticals Inc said the U.S. Food and Drug Administration granted a tentative approval to its generic epilepsy treatment Trokendi XR, sending its shares up as much as 164 percent.

The company said the U.S. FDA completed a review of Trokendi, an extended release version of Johnson & Johnson's widely used epilepsy drug Topamax, and did not seek any additional clinical trials.

Topamax is off patent protection and is available generically.

Topiramate, the generic name for Topamax, is currently available only in an immediate release form and is used as an adjunctive therapy for epilepsy and a treatment for migraine.

Supernus said the final approval of its drug depended on resolving a marketing exclusivity issue raised by the FDA regarding a specific pediatric population.

Mylan Pharmaceuticals Inc also markets an epilepsy drug that is a generic version of UCB SA's Keppra XR tablets.

Epilepsy is a medical condition that causes seizures affecting a variety of mental and physical functions, and affects about 2 million Americans, according to Centers for Disease Control and Prevention.

Rockville, Maryland-based Supernus is developing several other drugs for epilepsy, depression and attention deficit hyperactivity disorder (ADHD).

The stock, which has lost 12 percent of its value since the company went public in May, was up 137 percent at $13.56, making it the top percentage gainer on the Nasdaq. They touched a life high of $15.09 earlier in the session, valuing the company at almost $370 million.

More than 2.4 million shares had changed hands by 1137 ET, nearly 26 times their 10-day average volume.

(Reporting by Prateek Kumar in Bangalore; Editing by Roshni Menon)