Double-patenting and terminal disclaimer still can't stop generic Mirapex

Following a trial held in March, the US District Court for the District of Delaware held that Boehringer Ingelheim's patent for Mirapex (pramipexole dihydrochloride) was invalid for "obviousness-type double patenting". This product, which is indicated for the treatment of Parkinson's disease and Restless Leg Syndrome, has enjoyed annual sales in the US of approximately $380 million.

Both Barr Labs and, a little later, Mylan filed abbreviated new drug applications (ANDA) to manufacture a generic version of Mirapex in 2005, with paragraph IV certifications against the validity of Boehringer's US patents 4,843,086 and 4,886,812. Boehringer responded by filing suit against Barr and Mylan, and the cases were consolidated for trial.

The district court affirmed the principle that the same invention can't be patented twice. In this case the '086 patent -- which expired during the course of the litigation -- claimed methods of treating certain diseases by administering tetrahydrobenzthiazoles, while the '812 patent claimed the tetrahydrobenzthiazole compounds themselves, including pramipexole dihydrochloride. Said the court:

"Although there are differences between the '812 patent and the '086 patent, . . . those differences are insufficient to support the patentability of the '812 patent in light of the '086 patent".

Double-patenting may be avoided by making a terminal disclaimer. During the trial Boehringer terminally disclaimed

"...only the terminal part of the statutory term of the '812 patent which would extend beyond the 1,564 days after the full statutory term of the '086 patent as that term is defined in 35 U.S.C. § 154, so that by virtue of this disclaimer, the '812 patent will expire on October 8, 2010".

Boehringer received a 1,564 day extension under 35 USC § 156 due to FDA regulatory review of Boehringer's New Drug Application for Mirapex. As a result of this patent term extension, the original expiration date of the '812 patent, 12 December 2006, was extended to 25 March 2011. Thus, by its terminal disclaimer, Boehringer disclaimed five and a half months of patent term (the period of time between the expiration date of the '086 patent and the original expiration date of the '112 patent). According to Boehringer, its terminal disclaimer blocked Barr and Mylan's double-patenting argument. The court disagreed:

"A dual problem is presented in that the terminal disclaimer was not only filed at or near the conclusion of trial in this action, but it was also filed after the expiration of the earlier '086 patent. ...[F]or a terminal disclaimer to be effective, the earlier filed patent must not have expired at the time of the filing of the disclaimer"

Source: iStockAnalyst.