Apotex' generic version of Paxil would not infringe GSK's hemihydrate paroxetine patent because the generic does not contain a commercially significant amount of hemihydrate crystals, a Chicago district court decision says.

In the March 3 decision, Circuit Judge Richard Posner found GlaxoSmithKline's hemihydrate patent (4,721,723) to be valid, but not infringed by Apotex' ANDA for an anhydrous form of Paxil.

The case centered on the interpretation of claim 1 of GSK's '723 Paxil patent: "crystalline paroxetine hydrochloride hemihydrate."

While GSK argued that the presence of a single hemihydrate crystal in Apotex' generic paroxetine would infringe the '723 patent, Posner adopted a "looser" interpretation - that only a detectable amount would constitute infringement.

"I am inclined...to interpret [the patent claim] as excluding hemihydrate produced by involuntary conversion of a proportion of an anhydrous mixture so small as to lack any commercial significance," the court decision states.

"The presence of a single seed would not increase the value to consumers and hence the price that Apotex could charge for the anhydrate, or reduce Apotex' costs of production or sale, by even a Canadian penny."

If the court had agreed with GSK's "single crystal" claim interpretation, it would have ultimately invalidated the '723 patent due to indefiniteness.

"My construction produces a claim with definite, readily observable boundaries because Apotex' manufacturing methods...will produce hemihydrate, if any, in quantities far below the 'high double digits' level at which hemihydrate in a mixture with anhydrate attains commercial significance," Posner said.

Apotex' manufacturing plant was "seeded" with hemihydrate crystals when the generic company made hemihydrate in the course of developing its anhydrate paroxetine. The hemihydrate crystals became airborne and "contaminated" future product, the decision says.

To illustrate his point, Posner cited a theoretical example of a chocolate factory worker who takes Paxil on the factory floor, releasing hemihydrate into the air. Under GSK's interpretation, the presence of one crystal would cause the chocolate to infringe GSK's patent.

Apotex demonstrated that the amount of hemihydrate in its paroxetine anhydrate was below the level of commercial significance, the court said. "No recent batches produced by Apotex have been reliably shown to contain hemihydrate at the limit of detection (5%) of the standard tests."

"The hemihydrate that was found in small quantities in the anhydrate is not the same invention covered by patent '723; it is merely an impurity."

The court validated Apotex' argument that it is taking steps to keep the amount of hemihydrate of its Paxil generic to a minimum during large-scale production.

"Because Apotex has a powerful incentive to minimize the amount of hemihydrate in commercial production in order to avoid future suits for infringement, there may well be less hemihydrate in the scale-up than in the pilot phase of production," the decision maintains.

The court dismissed GSK's argument that Apotex was "usurping" its investment in Paxil. "Free riding is an integral part of the patent law," the court said. Generic competitors are "free riders with a vengeance. But they are lawful free riders. And so is Apotex."

GSK is appealing the decision. Final approval of Apotex' ANDA awaits expiration of 30-month stays triggered by two late-listed patents (nos. 6,113,944 and 6,172,233). The stays will expire in June 2003 and September 2003, respectively.

Apotex petitioned a Philadelphia district court to order GSK to delist the '944 and '233 patents from the "Orange Book" after the court granted Apotex' motion for summary judgment in December (¹ Also see "Apotex Paxil Generics Earliest Launch Date Could Be September 2003" - Pink Sheet, 6 January, 2003., p. 28). The court denied Apotex' motion on a third patent and dismissed all but one claim on a fourth. A trial date has not been set.

Following resolution of the Philadelphia case, Apotex believes it will be cleared to launch generic paroxetine no later than 2005. Apotex received tentative approval in May 2001 and believes it has rights to 180-day exclusivity. The '723 patent expires in 2006.

Apotex Paxil ANDA: Presence Of Hemihydrate Does Not Infringe GSK’s Patent

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