The Korean Supreme Court recently made a notable ruling concerning the validity of patents directed to enantiomer compounds. In Novartis v SK Chemicals, the Supreme Court reversed the Patent Court's finding that the Novartis patent is invalid, holding that the Patent Court seriously erred in judging the inventiveness of selection inventions.
In Korea, a selection invention is defined as an invention that is comprised partially or entirely of features (species) which are selected from a broader (generic) disclosure of the prior art. The Korean courts have formulated and applied a legal principle for selection inventions to determine the patentability of inventions that are based on the selection of a specific enantiomer from a known racemic mixture (Supreme Court Cases 2008Hu736 and 2008Hu3469).
According to this principle, (a) novelty is destroyed if the species is specifically disclosed in the prior art, or is recognisable from the prior art by a person skilled in the art, and (b) inventiveness can be established if the species shows either qualitatively different effects or quantitatively remarkable effects.
The patent at issue in Novartis (Korean Patent No. 133686) relates to the (−) enantiomer of N-ethyl-3-[(1-dimethylamino)ethyl]-N-methylphenylcarbamate, i.e., rivastigmine.Rivastigmine is marketed as Exelon for the treatment of Alzheimer's disease in Korea by Novartis.
One of the prior art references discloses a racemic mixture (RA7), a mixture of the (+) and (−) enantiomers of N-ethyl-3-[(1-dimethylamino)ethyl]-N-methylphenylcarbamate, and the medical use thereof as a potential treatment for Alzheimer's disease.
The Intellectual Property Trial and Appeal Board (IPTAB) held that the Novartis patent is invalid due to lack of novelty and inventiveness. In the decision, the IPTAB considered that:
- a person skilled in the art can easily recognise the enantiomers of RA7 since the prior art reference discloses that RA7 is useful as an anti-Alzheimer's drug and has one chiral center despite the absence of the terminology of enantiomers;
- a person skilled in the art would be motivated to select and resolve RA7 to obtain its individual enantiomers since biological activity data disclosed in the prior art reference shows that RA7 has beneficial effects; and
- the alleged effects such as transdermal absorption are not acknowledged as qualitatively different or quantitatively remarkable effects.
On appeal, the patent was also held to be invalid by the Patent Court. With regard to the inventiveness, the Patent Court concluded that a person skilled in the art can easily recognise the excellent transdermal absorption of RA7 and its enantiomers from the prior art further in view of common general knowledge, although there is no literal disclosure thereon in the prior art.
In contrast, the Supreme Court, overturning the judgement of the Patent Court, ruled that it should be recognised that the "transdermal delivery effect" of rivastigmine is a "qualitatively different effect" that a person skilled in the art cannot anticipate from the prior art. Detailed grounds are as follows:
- In view of the description, the claimed compound (rivastigmine) was shown to have excellent skin penetration when administered transdermally, and thus it is useful in treating Alzheimer's or Parkinson's disease via transdermal drug delivery.
- The prior art reference discloses biological activity data of RA racemic compounds including RA7; however, it merely describes that RA compounds may be administered in an oral or parenteral route, and fails to teach the effects resulting from the transdermal absorption of these compounds.
- Considering that the prior art reference discloses the acute toxicity data of carbamates for oral and subcutaneous routes only, it is difficult to recognize that the parenteral administration includes the transdermal administration.
- Although properties such as high lipid solubility, low melting point, short half-life, narrow therapeutic index, low molecular weight, and small dosage are attributes in the compounds having high transdermal absorption, it cannot be concluded that all compounds having such properties necessarily exhibit excellent transdermal absorption; thus, even though RA7 has the properties disclosed in the prior art, a person skilled in the art could not readily expect the excellent transdermal absorption of RA7 or its enantiomers.
- Therefore, the Patent Court erred in its decision by failing to acknowledge that the claimed compound has a transdermal delivery effect which is qualitatively different.
When assessing the inventiveness of enantiomer patents, a detailed factual analysis may be involved. In Korea, the key issue is whether a specific enantiomer has either qualitatively different or quantitatively remarkable effects in comparison to a known racemic mixture. In this case, the Supreme Court concluded that the transdermal delivery effect of rivastigmine is a qualitatively different effect.
This Supreme Court decision appears to reflect the recent tendency toward judgements in favor of the patentees.
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