In an application under the Patented Medicines (Notice of Compliance) Regulations (“Regulations”), Pfizer sought an order prohibiting the Minister of Health (“Minister”) from issuing a notice of compliance (“NOC”) to Ratiopharm for a generic version of the drug REVATIO (containing the medicine sildenafil citrate (“sildenafil”) – the same medicinal ingredient contained in VIAGRA) until after the expiry of the 324 patent. Ratiopharm alleged that the 324 patent was invalid for lack of soundly predicted utility, obviousness, and anticipation, and therefore that a generic version of REVATIO should immediately be allowed on the Canadian market for use in the treatment of pulmonary hypertension. Ratiopharm was ultimately successful on the first two grounds.
The doctrine of sound prediction requires the following three components to be satisfied where it is relied upon by a patentee to predict utility of a substance in advance of actual testing:
1. there must be a factual basis for the prediction;
2. the inventor must have at the date of the patent application an articulable and sound line of reasoning from which the desired result can be inferred from the factual basis; and
3. there must be proper disclosure, although it is not necessary to provide a theory of why the invention works. The soundness of the prediction is a question of fact.
In this case, all the experts unanimously agreed that the study disclosed in the 324 patent in support of sildenafil’s alleged ability to treat pulmonary hypertension (the 1024 Study) failed to provide enough information about the methodology of how the study was performed or conducted, and failed to provide any practical results that would enable a person skilled in the art to soundly predict sildenafil’s alleged utility. The 324 patent claimed to soundly predict the use of sildenafil in treating all types of chronic pulmonary hypertension by relying on a limited set of data from a few patients in one group. Although Pfizer had been studying the effect of sildenafil on patients suffering from important secondary forms of pulmonary hypertension, it did not wait for the results before filing the application for the 324 patent. Accordingly, the court found that Pfizer had not proven on a balance of probabilities that Ratiopharm’s allegation of lack of sound prediction was unjustified, and the 324 patent was therefore invalid on this ground.
With respect to obviousness, the main difference between the prior art and the 324 patent claims was that the prior art focused on rebound pulmonary hypertension in animals, whereas the 324 patent dealt with all forms of pulmonary hypertension. Pfizer submitted that while the mechanism of action for sildenafil had been understood for some time before the claim date, persons skilled in the art understood that just because it was biologically plausible that sildenafil could work didn’t mean that it was predictable that it would work to treat pulmonary hypertension in humans. The court found that this was therefore an appropriate case for applying the “obvious to try” test. It was self-evident that sildenafil would at least be effective in treating rebound pulmonary hypertension, a use explicitly included within the scope of the 324 patent. As such, there was a fair expectation of success that sildenafil would treat pulmonary hypertension, and it was therefore “obvious to try” sildenafil for this use. The 324 patent was accordingly also invalid on the ground of obviousness.