Validity of Selection Patents in South Africa

In a recent decision by the Supreme Court of Appeal of South Africa, the court looked at the requirements of disclosure for the purpose of deciding the validity of a so-called “selection patent”.

A selection patent is one which claims a specific subclass of a previously disclosed class of compounds, where the subclass has some special advantage which is peculiar to it as a whole. The main issue in this appeal was whether or not a generalised description (of the class) in a prior art document discloses a specific matter (subclass) covered by the selection patent in such a way which enables the skilled person to arrive at the claimed invention.

The prior art in question essentially teaches an avermectin compound for acting against parasites in the form of an injectable formulation comprising, amongst other things, a hydrophobic carrier, in which the avermetin compound is soluble. It generally lists a number of examples of suitable carriers or a combination of such carriers and specifically teaches, as a preferred example, a formulation using Triacetin on its own.

The patent in suit, on the other hand, specifically claims an injectable formulation which includes “a hydrophobic carrier comprising: (i) triacetin, benzyl benzoate or ethyl oleate or a combination thereof; and (ii) acylated monoglycerides, propyl dicaprylates/dicaprates, capylic/capric acids; trigylcerides, or a combination thereof.”

This specific combination of carriers results in a considerably prolonged duration of activity of 180 days (compared to the prior art example which lasted for 42 days). According to expert witnesses for the patentee, a skilled person could not arrive at the combination disclosed in the patent in suit by simply taking the prior art into consideration without significant ingenuity and experimentation. This is because the ingredients will react with each other and in the animal body in wholly unpredictable ways. This was not disputed by the respondent’s experts, but they stated that experimentation, not invention, would be required to arrive at the specific combination claimed. The court found that the prior art merely offers a “signpost” on the road to the invention, and there is something new which remains to be ascertained thereby making sufficient room for another valid patent. The revocation of the patent by the court a quo was thus set aside and the patent certified as being valid.

The full judgment can be accessed here

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