A US court has upheld a patent held by Johnson & Johnson for Risperdal, its drug for schizophrenia and bipolar disorder, protecting the product from generic competition until the end of next year.

US District Court Judge John Lifland has imposed an injunction on Mylan Pharmaceuticals and Dr Reddy`s Laboratories that prevents them selling generic versions of Risperdal (risperidone) in the USA until December 29 next year.

Risperdal is a major earner for J&J, bringing in more than $3.5 billion in sales last year.

The delay in generic competition to Risperdal is crucial for J&J, which is hoping to bring a follow-up, paliperidone, to market before the expiry in order to migrate patients to the new drug.

Paliperidone is designed to avoid the peaks and troughs of drug levels in the blood that occur with other antipsychotics and, hopefully, lead to improved control of symptoms. But the FDA asked for more information on the drug earlier this month, delaying its approval.