On August 29 2011 Justice Rennie of the Federal Court granted AstraZeneca an order prohibiting the minister of health from issuing a notice of compliance to Mylan Pharmaceuticals for a generic anastrozole product in AstraZeneca Canada Inc v Mylan Pharmaceuticals ULC.(1)


Anastrozole (AstraZeneca's Arimidex®) is a drug used for treating breast cancer. Anastrozole inhibits the enzyme aromatase, which is involved in the production of the hormone oestrogen. Cancers that rely on oestrogen for their growth – including certain breast cancers – can be treated by inhibiting aromatase.

The patent in issue, Canadian Patent Number 1,337,420, claims the compound anastrozole per se, as well as the use of anastrozole as an inhibitor of aromatase. Mylan alleged that the patent was invalid for lack of utility and obviousness.

On the issue of lack of utility, Mylan asserted that the patent made a three-part promise regarding the utility of anastrozole, namely:

  • the inhibition of aromatase;
  • therapeutic utility against oestrogen-dependent cancers; and
  • fewer side effects than aminoglutethimide (a previously known aromatase inhibitor).

Mylan alleged that, as of the June 15 1988 filing date of the patent, it had not been established that anastrozole fulfilled each of the above promises.


The Federal Court rejected Mylan's allegation of a three-part promise, finding that the patent made only one promise: inhibition ofaromatase. The court reviewed the patent specification, the expert evidence, the scientific context and prior jurisprudence construing promises of pharmaceutical patents, and concluded that the patent did not further promise therapeutic utility or fewer side effects than aminoglutethimide.

The court further found that two studies disclosed in the patent were sufficient to demonstrate the utility of anastrozole as an aromatase inhibitor. Accordingly, the court held that Mylan's allegation of lack of utility was unjustified.

On the issue of obviousness, the court ruled that anastrozole would not have been obvious, citing several factors, including:

  • the structural diversity of aromatase inhibitors, leading to the conclusion that there was no obvious starting point for the development of a new aromatase inhibitor;
  • the 'very unique' structures found in the anastrozole molecule; and
  • the fact that many other skilled groups were actively searching for new and better aromatase inhibitors, but failed to arrive at anastrozole.


Having rejected both of Mylan's invalidity allegations, the court granted AstraZeneca's application for a prohibition order, with costs. Mylan has appealed.

For further information on this topic please contact Daniel S Davies at Smart & Biggar/Fetherstonhaugh by telephone (+1 604 682 7780), fax (+1 604 682 0274) or email ([email protected]).


(1) 2011 FC 1023.