This is what an EEG looks like for someone with Lennox-Gastaut syndrome

H. Lundbeck A/S, maker of the antidepressant Lexapro, won U.S. approval for a drug to treat seizures associated with a rare and severe form of childhood epilepsy, Lennox-Gastaut syndrome.

The Food and Drug Administration cleared the add-on therapy called Onfi, the agency said today in a statement. The medicine, chemically known as clobazam, may reach annual sales of 1 billion kroner ($187 million), Anders Gersel Pedersen, head of research and development at Lundbeck, said in a phone interview today.

The disease known as Lennox-Gastaut syndrome is responsible for 1 percent to 4 percent of all childhood epilepsies and typically occurs from the ages of two to eight years old, according to the Copenhagen-based drugmaker. While many cases are hidden by patients’ parents, the disease affects about 10,000 to 15,000 children in the U.S., Pedersen said.

“Lennox-Gastaut syndrome is a severe form of epilepsy that causes debilitating seizures,” said Russell Katz, director of the FDA’s division of neurology products, in the statement. “This is a difficult condition to treat and it will be helpful to have an additional treatment option.”

The drug is taken daily in tablet form. A study of 238 patients with Lennox-Gastaut syndrome found that high doses of Onfi decreased weekly seizures an average of 68 percent compared with a placebo.

Decreased Seizures

Medium doses decreased weekly seizures 49 percent on average, Lundbeck said in a December 2010 statement after the trial. Patients who were being treated with at least one other antiepileptic drug experienced two or more seizures associated with a high rate of injuries each week.

Lundbeck intends to market the drug only in the U.S., where Onfi will be protected by market exclusivity.

The company will seek approval in Europe of its anti- alcoholism drug nalmefene by the end of the year and its antidepressant treatment LU AA21004 in Europe and the U.S. in the second half of next year, Pedersen said.