The High Court in Australia last week handed down its decision in the patent dispute regarding blockbuster cholesterol drug rosuvastatin (sold by AstraZeneca as Crestor).

Minter Ellison's clients, Watson Pharma and Ascent Pharma (now part of the Actavis / Allergan Group of companies), along with fellow generic pharmaceutical company Apotex, successfully defeated AstraZeneca's appeal against the judgment handed down by an expanded five judge bench of the Full Federal Court last year (you can find our note on that decision here).

The case is significant because rosuvastatin is the third most prescribed drug in Australia, and the most expensive by cost to Australia (taking into account both cost to Government through the PBS, and the cost to patients when filling a prescription). PBS figures show that the Australian Government spent almost $300 million on rosuvastatin in the 2013-14 financial year.

The High Court's decision concerns how to assess inventive step (obviousness) when a party seeking to invalidate a patent wishes to rely on the contents of a prior art document which doesn't form part of the common general knowledge.

Evidence to establish that the prior art document is sufficiently relevant would result from an expert witness conducting prior art searches (based on prior art available at the relevant priority date). Reviewing the search results typically requires a comparison between multiple documents, and a selection of the document/s which the expert considers relevant. However AstraZeneca argued that comparing search results was impermissible, and that the experts in this case giving evidence about obviousness in light of a prior art document they had identified as relevant had been "tainted" by information from other documents reviewed in the process of identifying the relevant prior art.

AstraZeneca's argument raised the unusual consequences that you would need a second independent expert to assess obviousness after a first expert had identified relevant document/s, and in some cases it may be impossible for an expert to identify relevant documents without undertaking a detailed comparison of search results.

In its judgment, the High Court has made clear that the exercise of finding relevant documents is separate to the test of combining any particular relevant document with the CGK to assess obviousness. An expert witness is allowed to use combinations of sources of information, eg reviewing multiple search results and considering what is disclosed in those documents, along the road to determining which document/s meet the relevance requirement (the first stage of the inventive step test). When deciding the question of obviousness based on the addition of one prior art document to the CGK (the second stage of the inventive step test), if that combination would lead the skilled person to the invention, it doesn't matter if other relevant prior art documents would lead away from the invention.

While the Court addressed AstraZeneca's arguments about inventive step in detail, the judgment confirms that there is no difficulty in interpreting the relevant sections of the Patents Act based on their plain and ordinary meaning, and does not make any substantive change to the law on inventive step in Australia.

Given the High Court unanimously dismissed the inventive step argument, it was not necessary for the Judges to consider AstraZeneca's second ground of appeal, regarding entitlement, nor any of the issues raised by the generic parties in a notice of contention (including the "starting point" issue which also arises when considering inventive step).

As a result of the decision, generic pharmaceutical companies (including Watson and Ascent) who were restrained from entering the market for more than a year because of an interlocutory injunction obtained by AstraZeneca in early 2012 can now seek compensation from AstraZeneca for the sales they would have made during that period.