Ranbaxy Pharmaceuticals Inc, the US subsidiary of the Gurgaon-based Ranbaxy Laboratories, has reportedly admitted infringement of the US-based Purdue Pharma's patent for the blockbuster drug, Oxycontin (oxycodone) in the District Court for the Southern District of New York, US.

The company has admitted the infringement following a para IV patent infringement suit filed by Purdue Pharma in October. The suits by the generic firms, lately, led to a multidistrict antitrust litigation against Purdue alleging that the company is engaging in sham patent infringement litigation to prevent generic competition for the opioid painkiller Oxycontin, the ninth most-selling drug in US in 2008. The patent under question, US Patent No. 5,508,042 covering controlled-released compositions of oxycodone is valid till April 2013.

Approving the consent judgement between Purdue Pharma and Ranbaxy without costs last week, Judge Sidney H Stein cleared that the present and future validity of the '042 patent in litigations involving Ranbaxy is established. The Court has also permenantly prohibited Ranbaxy from manufacturing or marketing the generic version of Oxycontin, which will in effect considered as infringement of the said patent. Ranbaxy has also agreed not to seek regulatory approval for marketing the generic version until the expiry of the patent or any period of exclusivity, according to reports. However, a query to Ranbaxy seeking response on the development has left unanswered till the time of filing of this report.

Purdue Pharma’s ‘042 patent entitled 'Controlled Release Oxycodone Compositions', which was issued on 16th April, 1996 covers a method for substantially reducing the range in daily dosages required to control pain in approximately 90 per cent of patients whereby an oral solid controlled release dosage formulation having from about 10 to about 40 mg of oxycodone or a salt of it is administered to a patient. The drug, a controlled-release medication meant to provide extended relief of pain associated with cancer, back pain, or arthritis, has recorded a sales of US$ 2.5 billion in 2008.

Ranbaxy submitted abbreviated new drug application (ANDA) No.78-093 to the US FDA under Section 505(j) of the Federal Food, Drug and Cosmetics Act seeking approval to commercially manufacture and sell oxycodone hydrochloride extended release tablets before the expiration of ‘042 patent, alleged Purdue in its complaint to the Court.

Ranbaxy submitted ANDAs for tablets in strengths of 10, 15, 20, 30, 40, 60 and 80 milligrams that contain oxycodone as active ingredient.

In November, 2009, Purdue Pharma has also settled a patent infringement suit with the Canadian generic firm, Apotex Inc, on the '042 patent rights. Apotex admitted infringement of the patent and was enjoined by the District Court for the Southern District of New York from marketing the generic version till expiry of the said patent. Purdue has been settling patent infringement lawsuit on OxyContin with several generic companies, so far including Endo, Teva, Impax and Mallinckrodt.

However, the opioid product has also many times attracted public and regulatory interest for frequent reports of drug abuse, putting the orginator company into troubles. The tablets are crushed and snorted, chewed, or mixed with water and injected- eliminating the time-release factor and allowing for a quick and intense rush to the brain.

A latest study, published in the Canadian Medical Association Journal in early this month, states that there was a five-fold increase in oxycodone-related deaths in Ontario, Canada, since the addition of long-acting oxycodone to the Ontario’s drug formulary in January 2000. The research was conducted by physicians at St Michael’s Hospital and the Institute for Clinical Evaluative Sciences (ICES) in Toronto. The lead author of the study, Dr Irfan Dhalla, comments that the oxycontin is a stronger opioid with higher risks even as the Purdue officials claim that the slow-release feature of the drug would lower the risk of users becoming addicted.

Earlier, in May 2007, the US federal court in West Virginia has imposed US$ 634 million penalty and sentenced three year's probation and 400 hours each of community service for three top executives of Purdue Pharma for making the drug available for illegal use than otherwise would have been available. In October, 2007, Kentucky officials sued Purdue because of widespread Oxycontin abuse in Appalachia violation of prescription requirements.