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Client Update: Extensions of term for pharmaceutical patents: the latest word

15 December 2009

In brief: The Full Federal Court's recent decision concerning the availability of extensions of term for pharmaceutical patents, particularly those claiming enantiomers, stands, following the High Court's rejection of a special leave application. Senior Associate Alexia Mayer reports.

Background

On 11 December, the High Court refused Lundbeck's application for special leave to appeal the Full Court's decision to uphold Justice Lindgren's decision that Lundbeck was not entitled to an extension of its 20-year patent term in H Lundbeck A/S v Alphapharm Pty Ltd [2009] FCAFC 70 (11 June 2009).

The patent in suit was Lundbeck's patent for escitalopram, a selective serotonin reuptake inhibitor (SSRI), a class of drugs used to treat depression and other mental illnesses. Lundbeck's product containing escitalopram, Lexapro, was registered on the Australian Register of Therapeutic Goods (ARTG) in 2003.

A racemate is a 50:50 mixture of two enantiomers, commonly referred to as the (+)-enantiomer and the (-)-enantiomer. Escitalopram is the (+)-enantiomer of the racemate citalopram. Lundbeck had caused the product containing the racemate citalopram, sold as Cipramil, to be registered on the ARTG in 1997.

An application for extension of term must be made within the time period specified in the Patents Act 1990 (Cth) (see subsections 71(2) and 70(3)). In the context of the Lundbeck case, the application needed to be made within six months after the first inclusion in the ARTG of goods that contain, or consist of, the pharmaceutical substance. A key issue in the Lundbeck case was whether the relevant ARTG registration date was that of Lexapro in 2003 or that of Cipramil on 1997.

Unfortunately for Lundbeck, the Full Federal Court upheld Justice Lindgren's decision that Cipramil (the racemate, being a 50:50 mixture of the two enantiomers) contained escitalopram (the (+)-enantiomer of the racemate), so the relevant ARTG registration was that of Cipramil. Accordingly, the time limit for applying for an extension of the patent had long since expired.

Justice Bennett (with whom Justice Middleton agreed1) explained the finding as follows:

...the pharmaceutical substance per se is the molecule, the (+)-enantiomer. The racemic mixture is a solution that contains both (+) and (-) enantiomers in equal proportions. The (+)-enantiomer molecule per se fulfils the requirements of s 70(2). It is the molecule that 'works' as a pharmaceutical substance alone, or together with other substances, in goods listed on the ARTG. These other substances may be components of a formulation or may otherwise be described as impurities, such as the (-)-enantiomer.

Justice Bennett reserved her position on whether a de minimis inclusion of the pharmaceutical substance in the ARTG listing would be sufficient for the purposes of subsection 70(3).

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What it means for you

Following the High Court's rejection of Lundbeck's application for special leave, it is now settled that, for the purposes of the extension of term provisions, a racemate 'contains' each of the two enantiomers. Accordingly, if a racemate has been included on the ARTG, it will be the date of that ARTG registration that is relevant when applying for an extension of term for a patent covering an isolated enantiomer of that racemate.

Many new medicines developed today are close chemical relatives of existing medicines. When considering applying for an extension of term for a patent, pharmaceutical companies should consider whether the pharmaceutical substance claimed in that patent could be said to be 'contained' in an older medicine, as a component of a formulation or as an impurity.

For further background on seeking extensions of term for pharmaceutical patents, please see our Biotech Bulletin article: Patent extensions for pharmaceutical substances: when do registered goods 'contain, or consist of' a pharmaceutical substance?

Footnotes
  1. Justice Emmett did not find it necessary to decide the extension issue because he had found the claims invalid. However, his Honour indicated that he would have been inclined to uphold Justice Lindgren's conclusion.

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