US drug-maker Cephalon has filed a patent infringement suit against Lupin Pharmaceuticals, a unit

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of BSE-listed Lupin, to keep generic versions of popular sleep disorder drug Nuvigil off the market.

Cephalon filed the complaint in the US District Court for the district of Delaware this week stating that Lupin's generic version infringes Nuvigil patents. This automatically puts a 30-month stay on Lupin's US unit to sell generic Nuvigil. Nasdaq-listed Ceph-alon is trying to litigate to slow the market entrance of cheaper copycat versions of Nuvigil while it continues to transition patients from its older narcolepsy drug Provigil to Nuvigil. Cep-halon derived 48 per cent of total sales, or almost $961 million, from Provigil in 2009.

“Cephalon markets Nuvigil as a chemically similar drug but with longer-lasting effects. Cephalon launched Nuvigil in June 2009 and recorded $73 million in US sales in the calendar year,” said a senior pharma analyst at a foreign brokerage.

If a generic manufacturer wants to begin selling a pharmaceutical drug before the innovator company’s patent is expired, the generic can file an abbreviated new drug application (ANDA) with the FDA along with a paragraph IV certification. Once an ANDA is filed, the patent holder has a strong incentive to act quickly to charge the generic with infringement. If charges are filed within 45 days, an automatic statutory stay is triggered that delays approval of the generic’s ANDA for 30 months. This is exactly what has happened in case of Lupin Pharmaceuticals versus Cephalon.