Reduced Dosage Form of Tadalafil Obvious to Try

Eli Lilly Canada Inc. v. Mylan Pharmaceuticals ULC / tadalafil (NOC) 2015 FC 125 de Montigny J
            2,371,684 – tadalafil dosage form – CIALIS

In this NOC proceeding de Montigny J held that Lilly’s tadalafil dosage form patent was invalid for failure to satisfy the promise of the patent, as being anticipated, and for obviousness. While the decision raises some interesting legal points regarding the promise of the patent, anticipation, and prosecution history estoppel, the holding respecting obviousness was quite straightforward and it is convenient to begin by discussing that aspect of the case.

Both sildenafil and tadalafil were known in the prior art for the treatment of ED. Lilly’s ‘784 patent, claiming tadalafil for the treatment of ED, disclosed unit doses of tadalafil from 0.2 to 400 mg [4] (and see 2015 FC 17, blogged here, holding the ‘784 patent to be valid). Sildenafil was marketed in doses of 25 mg, 50 mg, and 100 mg, with 100mg being the most common dose [6], [10]. Sildenafil has a variety of side effects, including flushing, vision abnormalities, and a negative interaction with nitrates that are used to treat heart conditions [6]. Early studies with tadalafil used 100mg doses. Lilly researchers discovered that despite being equipotent with sildenafil, tadalafil did not need high doses, and lower doses of tadalafil could be used effectively and with reduced side effects. This discovery was the basis for the ‘684 patent [12]..

There was some debate as to whether the inventive concept included reduced side effects, or was simply a dosage of less than 20mg for the treatment of ED [164]. If the inventive concept was simply the dosage, then it seems to me that it must be obvious, as the ‘784 patent disclosed that dosages of tadalafil including that range would effectively treat ED, so there would be no technical contribution to what was already known. For the invention to be non-obvious, there must be something surprising about the claimed dosage range, such as unexpectedly reduced side effects. In any event, de Montigny J did not need to resolve this debate as he found that the invention was obvious even if the inventive concept included reduced side effects. He found on the facts that in drug development it is standard practice to lower the dosage to reduce side effects [168] and there is a standard process for determining a minimal effective dose [169], so it would have been routine for a skilled person to carry out a dose escalation study starting at 5mg and moving up to 50mg [170]. Even though the optimal dosage regime could not have been predicted in advance, that lower dosages were effective with reduced side effects was the unsurprising outcome of a routine research program that a skilled person would be motivated to carry out [172]. This is a classic case of an invention that is obvious to try. Lilly argued that a skilled person would not have been motivated to try doses of less than 50mg, but de Montigny J rejected this on the facts [165].