Mumbai-based Sun Pharmaceuticals has filed a post-grant opposition with the Mumbai patent office against a product patent granted to the extended release version of Johnson and Johnson's (J&J) blockbuster drug Risperdal, used in the treatment of psychological disorders and schizophrenia. Risperdal, with the molecular name risperidone, is the second-largest selling drug of Johnson and Johnson with over $4.5 billion worldwide sales in tablet, injection, syrup and orally dispensable forms. It is also one among the largest selling psychiatric drugs, according to sources. Sun Pharma has been marketing a generic version of this drug for the last few years in India under the brand name Sizodone, according to company sources. The patent on Risperdal, granted in February 1986, will expire in the US on June 29, 2008. The Indian patent was for an extended release version and this had not been patented in the US, said patent experts having knowledge of the development. Patent wars Swiss drug maker Roche's anti-cancer drug, Pegasys, was given a patent in India in 2006 and this was challenged by Wockhardt and a Mumbai-based non-governmental organisation, Sankalp. Generic drugmaker Cipla is battling in the Supreme Court to revoke a patent granted in February 2007 to Roche's cancer drug Tarceva. Another patent granted to Roche's anti-HIV drug, Valganciclovir, is also being challenged in the court by Lawyers Collective, a Mumbai-based NGO, and Cipla. According to the Indian Patent Act, which was amended in 2005, a product patent that bars other companies from copying the drug for generics, can be challenged within one year. The Mumbai patent office granted a patent to Janssen Pharmaceutica, a group company of Johnson and Johnson, on July 20, 2007, with patent number 208191, against its mail box application number 188AL/1995. The patent related to sustained-release particles of risperidone, said sources. Company sources declined to reveal the sales figures for the drug in India. "We don't comment on litigations and patent-related issues as a matter of policy,' said a Sun Pharma spokesperson. Interestingly, Dr Reddy's Laboratories and US-based Mylan Laboratories were among the first to challenge the patent on Risperdal in the US, where the drug has sales of over $2 billion, said sources. "Since the product patent regime was introduced in India in 2005, we estimate that more than 150 product patents have been granted and over 90 per cent of this is for multinational pharmaceutical companies. So far, very few products have been opposed by Indian companies, according to our knowledge,' said Varun Chonkar, a patent expert. He said the Indian patent office was yet to officially announce data on the number of patents granted and challenged in India.