Obviousness and Inherency in Solid Forms

Claimed inventions in issued patents must, of course, pass the statutorily required hurdles of novelty and non-obviousness. In the context of solid forms, there are particular nuances the practitioner should consider when formulating a strategy for obtaining such claims in the United States. This article touches upon novelty and obviousness matters which have arisen with solid-form patents and provides some food for thought on how to plan in advance to tackle these issues.

1. Obviousness

In Grunenthal GMBH v. Alkem Labs. Ltd., the plaintiffs sued Alkem, Hikma, and Actavis, alleging that the defendants’ attempts to market generic versions of immediate-and-extended-release tapentadol hydrochloride would infringe U.S. Patent Nos. 7,994,364 (the ‘364 patent) and 8,536,130 (the ‘130 patent) (919 F.3d 1333 Fed. Cir. 2019). The ‘364 patent claims Form A of tapentadol hydrochloride, while the ‘130 patent claims a treatment for polyneuropathic pain with tapentadol hydrochloride (Id. at 1336). Interestingly, the prior-in-time form of tapentadol was known as Form B and is disclosed in United States Patent Number 6,248,737 (the ‘737 patent).

Example 25 of the ‘737 patent teaches the synthesis of tapentadol hydrochloride and states the result is crystalline, but provides no further details related to the structure of the crystal or whether it is polymorphic. The defendants also presented another prior art reference, a 1995 article by Professor Stephen Byrn of Purdue University, which teaches a “conceptual approach” to identifying pharmaceutically useful solids (Id. at 1337). The article includes a flow chart describing steps to be taken in determining the potential polymorphism of a particular API. Importantly, the article further teaches how many variables, including temperature, concentration, pH, and choice of solvent, can affect polymorph formation and characterization (Id. at 1337 Fed. Cir. 2019).

On appeal, the Federal Circuit considered whether the combination of these two references— the Form B tapentadol hydrochloride patent (‘737 patent) and the teachings of Byrn—rendered the Form A Patent invalid for obviousness. In upholding the district court, the Federal Circuit ruled that the prior art failed to provide a reasonable expectation of success.

Because the record indicates that there was (1) no known or expected polymorphism of tapentadol; (2) no evidence that the synthesis of Example 25 results in any Form A; and (3) no guidance as to what particular solvents, temperatures, agitation rates, etc., were likely to result in Form A, Alkem failed to prove that a POSA would have reasonably expected a polymorph screening of the Form B disclosed in the ‘737 patent to result in Form A.

(Id. at 1343). The prior art fared no better under obvious-to-try. The court concluded that there were a “huge number of possible choices” provided in a general teaching without “detailed enabling methodology” which did not fall within KSR v. Teleflex’s “finite number of identified, predictable solutions” (Id. at 1345).  Taken together, KSR and Grunenthal suggest that the genus-species approach and the natural unpredictability of solid form based on the prior art provide substantial grounds for a robust patent strategy under the right scientific and technical circumstances.

While Grunenthal relates primarily to the prima facie case, the thoughtful practitioner will also consider arguments directed to secondary considerations, most notably, unexpected results. Since in other jurisdictions, most notably in Europe, unexpected results are of crucial importance with solid-form patents, having such arguments available in the United States too is prudent. Fortunately, there is much that is unexpected with solid forms, such as dissolution, hygroscopicity, stability, and the like.

2. Inherency

While obviousness attacks have emerged more recently in solid-form patent disputes, the inherency specter may await lurking for the unprepared. Where inherency is relevant, it often emerges based on the patentee’s own prior art. In SmithKline Beecham v. Apotex, the court held that the practice of the prior art paroxetine compound patent led to the creation of the claimed crystalline paroxetine hydrochloride hemihydrate (403 F.3d 1331 Fed. Cir. 2005). In that case, the prior art was the free base of paroxetine rather than another hydrochloride salt, an important consideration not addressed. In a more traditional inherency context, the prior art teaches either (a) Compound X and its synthesis and is silent as to form or (b) there is a crystalline form but without structural detail. Later, a polymorph screen is done, and several crystalline forms are found, and a patent application is filed. The issue becomes whether one of those new forms is in fact the crystalline material prepared but never characterized in the prior art. If yes, then that form is inherently anticipated and cannot be patented. The legal question depends on an intensely factual determination as to what that form was and may require the reproduction of the reference to provide some evidence. While beyond the scope of this paper, litigation can hinge on whether the examiner can shift the burden to the applicant to show that a prior art reference is not anticipated.

Coordination is Key

In conclusion, as with much in the life sciences, preparing for novelty and non-obviousness arguments often involves coordination among patent practitioners and inventors/scientists to chart the best path forward.

For more on this topic, tune in to IPWatchdog’s webinar on April 28, “Patenting and Litigating Pharmaceutical Salts.”

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