Eisai has been granted approval by the US Food and Drug Administration (FDA) to market its new epilepsy drug Fycompa in patients aged over 12 with partial onset seizures.
Fycompa (perampanel) is the first drug to be approved for marketing in the US that works as a non-competitive AMPA-type glutamate receptor antagonist.
The drug stops over-excitement of neurons by blocking the binding of neurotransmitter glutamate to post-synaptic receptors in neural pathways thought to be important in many forms of epilepsy.
Eisai has high hopes for perampanel's prospects, predicting earlier this year that the drug could achieve $500m in sales by 2015, rising to $1bn or more at peak, if it gets approval in major world markets.
The company already has a successful epilepsy franchise with drugs such as Zonegran (zonisamide) and Zebinix (eslicarbazepine), and has said perampanel is central to its aim to become a top-three company in the therapeutic category.
Approval of Fycompa in the US came on the back of data from three phase III trials of the drug as an adjunctive treatment of partial-onset seizures - the most common type of seizure in epilepsy - with or without secondarily generalised seizures.
The studies showed that Eisai's drug cut seizure rates in these patients, with a 50 per cent reduction seen in around a third of patients treated with perampanel compared to 20 per cent or fewer of those on placebo.
Eisai has already been approved in Europe and reached its first markets earlier this year, but had a trickier path to approval in the US.
The FDA turned down Eisai's marketing application for the drug in July, 2011, asking for a re-analysis of data from its trials, but accepted a re-filed application in March, 2012.
"Some people with epilepsy do not achieve satisfactory seizure control from treatments they are currently using," commented Russell Katz, director of the division of neurology products in the FDA's Center for Drug Evaluation and Research (CDER).
"It is important to have a variety of treatment options available for patients with epilepsy."