The big drugmaker failed to win a summary judgment as it races toward a February 2010 trial over the patent for its blockbuster cholesterol pill. The US District Court for the District of Delaware rejected its motion to dismiss claims of inequitable conduct, which were made by several generic drugmakers seeking to invalidate Crestor’s ‘314 patent. The main US patent runs until 2016 (see ruling here).

The generic drugmakers - Apotex, Aurobindo, Cobalt, Mylan, Par, Sandoz and Sun - contend material info was omitted when the original Crestor patent was filed by AstraZeneca’s partner Shionogi and this was inequitable conduct. AstraZeneca denies the charge.

In an investor note, Leerink Swan analyst Seamus Fernandez wrote that, in redcated documents, a patent attorney who worked briefly for Shionogi couldn’t recall considering filing prior art references (prior art is the info made publicly available before a given date that might be relevant to patent claims of originality. If an invention has been described in prior art, a patent on that invention is not valid).

The generic drugmakers contend they “elicited testimony which would prove Kitamura intended to disclose the prior art reference but ran out of time. Stark believes the key question regarding (the attorney) is why did she leave her employment with Shionogi and, had she not done so, would she have disclosed the prior art at issue?” Fernandez wrote.

The second key witness was a Shionogi patent attorney who was involved in managing other Shionogi patent attorneys and AstraZeneca claims this attorney was new to managerial responsibilities and was operating in a chaotic environment which led to an inadvertant and unintentional failure to disclose, according to Fernandez.

Stark notes that the attorney held onto European Search Reports, which contained the prior art references for a period “longer than usual,” and cited inconsistencies with Shionogi’s prosecution of US & EU patents that will need to be decided by an appropriate fact finder.

“We still believe the odds favor AstraZeneca, given the high hurdle involved in proving inequitable conduct, but the hearing and subsequent recommendation have raised our risk threshold regarding the outcome,” Fernandez concluded.