Pfizer has failed in a legal bid to force US generics company Mylan Laboratories to drop inequitable conduct claims in a lawsuit between the companies, ensuring that the patent infringement case – involving Pfizer’s $2.5 billion dollar blood pressure drug Norvasc (amlodipine besylate) – will go to trial.

Pfizer had asked the US District Court for the Western District of Pennsylvania to dismiss Mylan’s claims that Pfizer behaved improperly in its defence of Norvasc. Mylan already has approval to market a generic version of Norvasc [[05/10/05c]], but has been blocked from doing so by two additional patents that expire on January 31, 2007 and September 25, 2007.

Mylan insists that Pfizer has acted improperly in getting the patents awarded. In US patent law, inequitable conduct generally means that a patent applicant has misrepresented information or left out pertinent facts to get a patent approved.

In a separate ruling, the court also denied Mylan's motion to invalidate one of the patents.

The court ruled that "both Pfizer and Mylan have raised a number of persuasive arguments as to the issues of the alleged inequitable conduct by the Pfizer patent applicants" during the prosecution of both patents.

Mylan has already received final approval from the US Food and Drug Administration for all strengths of amlodipine, and has been confirmed as the first generic company to file and therefore eligible for 180 days of market exclusivity on all strengths.

However, the generics company runs the risk of punitive damages if it launches amlodipine besylate before the patent issues are resolved.

For Pfizer, another year’s patent protection for Norvasc would help it weather a difficult period when a number of its other top-selling products – including the antifungal agent Diflucan (fluconazole), the epilepsy drug Neurontin (gabapentin) and the antidepressant Xoloft (sertraline) – are facing generic competition [[01/12/04a]]. $14 billion in annual revenues are under threat, according to the company.