It was a big day for Johnson & Johnson’s legal teams yesterday as the drugmaker attempted to block the launch of generic versions of its Topamax epilepsy drug, and started drawing up the defense for its oral solution formulation of blockbuster schizophrenia treatment Risperdal.

The most pressing threat to its business came from Mylan Laboratories, which last month won US approval to sell generic versions of three Topamax doses with combined annual sales of approximately $1.4 billion.

J&J was trying to win an injunction against the launch of Mylan’s generic last night and had asked for an initial hearing to put its case forward.

Mylan is thought to be debating whether to launch its generic, which could provide enormous near-term revenues but also ay it open to sizeable damages should it lose an ongoing patent infringement lawsuit filed by J&J.

As the first to file for approval of generic Topamax, Mylan has six months’ exclusivity in the marketplace so could reap a rich harvest before other generics enter the field.

J&J has always insisted that its Topamax patents are valid until 2008, so could lose two years of blockbuster sales should Mylan prevail in the patent infringement suit.

Risperdal rival

Meanwhile, Teva Pharmaceutical Industries said yesterday it had won tentative approval from the US Food and Drug Administration for its generic version of Risperdal (risperidone) Oral Solution.

Tentative approval means that the agency has reviewed the filing and found it acceptable, although full approval cannot be granted until the expiry of patents covering the formulation, or their invalidation through legal action.

Teva said it expects final approval in December 2007, when patents on the branded product expire. Sales of Risperdal Oral Solution in the USA are approximately $66 million a year at present, according to the Israeli firm.