The Full Federal Court has recently handed down its decision in the appeal by Otsuka Pharmaceutical Co (Otsuka) against the earlier finding by Justice Yates that Otsuka's patent relating to aripiprazole, a drug used in the treatment of schizophrenia, is invalid for want of novelty and inventive step.

Significantly, the patent claims asserted by Otsuka focused on the use of aripiprazole to treat the cognitive impairment caused by "disorders of the central nervous system which are associated with the 5-HT1A receptor", in patients failing to respond to specified antipsychotic drugs.

Otsuka relied heavily upon the patent claims' reference to the 5-HT1A receptor in arguing the patent's validity. Up until this point, the effects of aripiprazole in patients suffering from schizophrenia had been described in the prior art, however the role played by the 5-HT1A receptor in achieving those effects had not. Otsuka argued that the association between schizophrenia-related cognitive impairment and the 5-HT1A receptor (the association feature) was an independent, essential feature of its claims which underpinned its validity.

The affliction of parameteritis

At first instance, Justice Yates rejected Otsuka's argument and found that the patent claims lacked novelty and were not directed to a new therapeutic use of aripiprazole, but to the same use.

The Full Court upheld Justice Yates' finding. Justices Besanko and Nicholas rejected Otsuka's argument that a natural reading of the patent claims taught that there were two classes of cognitive impairment, namely those that are and those that are not associated with the 5-HT1A receptor. Their Honours instead construed the association feature as being descriptive of the kinds of disorders there identified.

In his separate judgment, Justice Beach concluded that the association feature, were it a separate integer of the patent, would have infected the patent with parameteritis. Parameteritis refers to an attempt to re-patent the prior art by limiting claims by reference to a series of parameters not mentioned in the prior art. According to his Honour, the association feature added nothing new to the invention, but merely stated an existing scientific theory which posited the link between the 5-HT1A receptor and the disorders that are treated by aripiprazole. In this sense, Otsuka's patent did not create a new process or method, it merely claimed an old use of an old product. His Honour stated that the "artificiality" and "nebulous verbiage" of the patent's claim gave him confidence that the claim was not an essential integer.

Conclusion

It remains to be seen whether Otsuka will seek special leave to appeal to the High Court of Australia, however the Full Court's decision represents a cautionary tale for patentees seeking to extend their effective monopoly by filing further patents containing Swiss-type claims.