A Markman ruling issued by Judge Andrews this week demonstrates how hard it can be to convince the Court that a patentee has disclaimed claim scope. In the MDL In re: Sitagliptin Phosphate ('708 & '921) Patent Litigation, Judge Andrews drew a distinction between the kinds of prosecution activity that can give rise to disclaimer, and those that cannot.
In short, defendants argued that the plaintiff had disclaimed claim scope regarding the nature and purpose of the claimed "surfactant" during prosecution. The Court ultimately agreed in part, finding that "surfactant" had been limited to a "wetting agent" that increases dissolution of sitagliptin.
It is worth noting here that disclaimer can be a powerful tool. Unlike prosecution history estoppel, for example, which limits the scope of equivalents, disclaimer limits the literal scope of the claims, making it a tempting reach for defendants. However, the standard is difficult (it requires unequivocal disavowal of scope).
Judge Andrews' ruling is a good illustration of the kind of prosecution history that suffices to meet the exacting standard for disclaimer. According to his analysis, the patentee made statements limiting the scope of "surfactant" in response to rejections over four separate prior art references and in a submission by the plaintiff's director of formulation.
Nonetheless, Judge Andrews rejected part of defendants' proposed construction (the portion that would have required dissolution of sitagliptin and metformin in a a single granulation) because that limitation on scope was supported by "single, 'passing reference'" to that limitation.
Later in the ruling, he rejected a separate disclaimer argument, finding (among other things) that there was "more than one possible reasonable understanding of the supposed disclaimer," including that they might have been directed at different, narrower claims, another pitfall for supposedly "unequivocal" statements.