AstraZeneca has won a US district court ruling in defence of its patent extension for the extended-release version of its antipsychotic drug Seroquel (quetiapine).

After the failure of AZ’s challenge to the FDA’s decision to allow generic competition to Seroquel, the ruling by a district judge in New Jersey gives the UK drug company a significant legal boost.

In addition, a US district judge in Columbia has ruled against allowing AZ a temporary restraining order (TRO) against generic competitors but has criticised the FDA for lack of fairness and transparency.

AZ is seeking an extension of the recently-expired Seroquel patent to cover its extended-release version, Seroquel XR, until December 2012, but the validity of the extension has been denied by a UK court and by the FDA.

US District Judge Joel Pisano in Trenton, New Jersey, ruled that four generic drug manufacturers – Mylan, Anchen, Osmotica and Torrent – have infringed on a valid patent for the extended-release version of quetiapine.

While the generic companies argue that the extended-release formulation applies technology that is in widespread use, Pisano accepted AZ’s argument that only its formulation of Seroquel XR proved it was effective in this case.

In addition, he noted, AZ had achieved a new indication for the XR version as a treatment for bipolar disorder.

Seroquel generated $5.83bn for AZ worldwide in 2011, including $1.4bn from Seroquel XR. However, low-cost generic competition from the above companies and from Teva in Europe threatens to affect AZ’s 2012 revenue severely.

AZ has already settled patent infringement disputes with two other companies, Handa and Intas, which will launch generic copies of Seroquel in 2016.

In a balanced statement on the dispute, Judge Beryl A. Howell of the US District Court for the District of Columbia denied AZ’s request for a TRO on generic versions of Seroquel, but criticised the FDA for unfair handling of the case.

Judge Howell concluded that AZ “has not demonstrated a likelihood of success on the merits, particularly given the deference the Court must provide to agency actions and interpretations of its own organic statute.”

However, she commented that the FDA appeared to have made a “tactical decision” to block AZ from seeking a judicial review of the Agency’s decision. The FDA’s statements “could appear to be less than forthright about the status of FDA decision-making,” she commented.

As a result of “the FDA’s tactics of ‘hiding the ball’ of its position until March 27, 2012,” Judge Howell stated, “consideration of the merits of the legal issues presented by the plaintiff’s complaint has been delayed”. She ordered the FDA to supplement the administrative record with any additional relevant records.

AstraZenca’s lawsuit against the US FDA over its decision not to block the entry of generic versions of Seroquel and Seroquel XR (quetiapine fumarate) has been called a gamble.

AZ claims the FDA cannot approve any generic versions of the blockbuster brands that lack specific label safety warnings – which the pharma company holds exclusive rights to.

But Ana Nicholls, Healthcare Analyst at the Economist Intelligence Unit, says the move could backfire and end up damaging AZ’s relationship with the US health regulator.

The FDA denied a Citizen Petition filed by the pharmaceutical company on March 7^th. AZ requested in September 2011 that generic versions should not be allowed to enter the market until December 2^nd 2012, when data exclusivity expires.

But the Agency’s denial of the Petition has led to AZ saying it will “vigorously defend its legal rights”.

It is now seeking an injunction preventing the FDA from granting final marketing approval of generic versions until the start of December or, alternatively, until a federal court has had the opportunity to review the FDA’s action regarding the pending generic marketing applications.

Generic competition cost the company almost $2bn in revenue last year, it calculates. Seroquel generated sales in the US worth $3.3bn in 2011 and could earn additional revenue of $650 million if AZ gets its way.

If the lawsuit is successful, Ana Nicholls predicts the move may be used by other pharmaceutical companies looking to protect or extend patent exclusivity. “If AZ does succeed in its argument over labelling requirements and data exclusivity rights, then this might give it (and other companies) another way of extending protection for drugs that are coming off patent,” she said.

“Other companies have tried different tactics – Pfizer, for example, struck exclusivity deals with pharmacy benefits managers to protect sales of Lipitor after its US patent expired late last year.

“But with the mood in the US firmly against attempts by patented drug-makers to block generic competition, the likelihood of AZ winning its case seems remote, raising the question of how much its lawsuit may damage its relationship with the FDA.”

The patent covering the active ingredient in Seroquel and Seroquel XR expired in September 2011, with paediatric exclusivity expiring on 26 March 2012. Seroquel XR is covered by a formulation patent that expires in May 2017, with paediatric exclusivity expiring in November 2017.

Last year, AstraZeneca agreed a licensing deal with generic firms Handa and Accord to enter a generic version of Seroquel XR in the US market on November 1^st 2016, or earlier under certain circumstances.