Eli Lilly's Erectile Dysfunction Patent Stands Up To Scrutiny

The English High Court (Patents Court) has ruled in a patent dispute concerned with the treatment of erectile dysfunction. Actavis and Mylan had commenced "clear the way" litigation by seeking to revoke Eli Lilly's patent in order to launch generic versions of its CIALIS medicine upon expiry of the relevant SPC protection (November 2017).

One of Eli Lilly's patents, regarding the dosage of CIALIS (EP(UK) 1,173,181), was found to be valid and infringed. The other patent, regarding microparticulate formulation of the active ingredient (tadalafil) (EP(UK) 1,200,092), was invalid.

The case involved multiple claimants, including Actavis and Mylan, across several joined cases. The judgment is long and complex, but there are some take-home messages for patentees and potential litigants that should not be missed.

The burden of establishing legal priority

Firstly, when considering validity, a particular dispute formed around whether a piece of prior art ("Stoner") could be citable against Lilly's dosage patent. Stoner was an international ("PCT") patent application filed by a third party (Merck) and was a co-pending patent application with the patent in suit. As such it could be only be cited for the purposes of a novelty attack under s.2(3) of the Patents Act 1977 ("PA"). However, it would only count as prior art against the patent if the PCT was entitled to its claimed priority.

To establish priority, two things are required; substantive and legal priority. Substantive priority is concerned with whether the "same invention" is disclosed in the priority document as the patent under scrutiny, whereas legal priority is concerned with whether the proper legal formalities have been followed to establish a chain of documents through which priority can be claimed.

Substantive priority of Stoner was not in issue, but legal priority was disputed. Was the documentary chain of title in order? And who had the burden of establishing this? Birss J considered this and found that the legal burden of proof lay with the Claimants, as the parties attacking validity. However, if sufficient evidence was available to support an inference that legal priority existed, the evidential burden would shift to the party (Lilly) seeking to rebut that inference.

The Stoner applicants were Merck & Co and Ms Waldstreicher. Ms Waldstreicher was also named as an inventor. The applicants on the face of the priority document were Ms Waldstreicher and Ms Stoner. The judge noted that...