2,370,565 / calcipotriol & betamethasone / DOVOBET
In this NOC proceeding Locke J granted an order of prohibition as infringement of multiple claims was conceded, and he held that Teva’s allegations of obviousness, lack of utility and insufficiency were not justified . The holding turned on the facts of the case, but the claim construction argument raises the question of the continued vitality of Minerals Separation.
The claimed invention is a dermal cream formulation for the treatment of psoriasis. Vitamin D and vitamin D analogues, specifically calcipotriol, were previously known for treatment of psoriasis, as were corticosteroids (such as betamethasone), and these were commonly used sequentially. There was consequently a motivation to develop a combined formulation, but the two drugs could not simply be mixed because they were pH incompatible, which is to say that calcipotriol was unstable at any pH value which was favourable to the stability of a corticosteroid, and vice versa , , . Leo discovered a stable formulation containing these compounds plus the solvent POP-15. Claim 1 was to a formulation comprising vitamin D or a vitamin D analogue (component A), a corticosteroid (component B) and a solvent selected from a large class, while Claim 17 specified POP-15 as the solvent. (Claim 17 was the only claim held to be useful and infringed. The utility of the other infringed claims was not addressed.)
The patent itself disclosed that a formulation using propylene glycol as a solvent was unstable . Teva argued that because the wording of the claims is non-exhaustive (using "comprising") and there is nothing in the claims to suggest that they are limited to compositions that are useful in treating psoriasis, the claim should therefore be construed as encompassing formulations with an additional component, such as propylene glycol, which would not be useful . More generally, if Teva’s argument were sound, any claim using “comprising” language would be invalid unless it was expressly limited to safe or effective formulations, as a claim not so limited would encompass the formulation plus Compound X, where Compound X is a poison.
Locke J rejected this argument:
 In addition, with regard to propylene glycol, reading the 565 Patent as a whole, the skilled person would note that a composition using propylene glycol as the solvent was not stable. Bearing in mind that the skilled person is trying to achieve success and not looking for difficulties or seeking failure, s/he would be inclined to avoid using a compound that had been shown not to work. The skilled person would likewise avoid using other compounds that were known to interfere with the purpose of the patented ointment (to treat psoriasis), even though the claims do not explicitly exclude such interfering compounds.
In my view, Locke J’s reasoning is sound, but we should acknowledge a tension with some prior authorities.
In Norton and Gregory v Jacobs (1937) 54 RPC 271, 276 (CA) Greene MR said :
The fact that a skilled chemist desiring to use the invention would reject certain reducing agents as being unsuitable is one thing; it is quite a different thing to say that a claim must in point of construction be cut down so as to exclude those reducing agents because a skilled chemist would not use them. To adopt the latter proposition would not be to construe the Specification but to amend it.
This was subsequently quoted with approval in Minerals Separation, (1952) 69 RPC 81, (JCPC) aff’g  SCR 36 rev’g 12 CPR 99 (Ex Ct). The claim was to xanthates for separation of minerals from ores by froth floatation and the evidence established that at least one class of xanthate, namely cellulose xanthates, actually interfered with that process. It appears that a skilled person would have known or readily realized this, as it was known that cellulose xanthates would form a colloid which should normally be avoided in froth flotation. Holding the claim invalid, Lord Reid in the Privy Council stated that “It is well settled that, where the scope of a claim includes some method which is useless, the claim cannot be saved by showing that no skilled person would ever try to use that method” (95). Thus Locke J’s holding in this case appears to be inconsistent with Minerals Separation.
Minerals Separation was distinguished by the SCC in Burton Parsons  1 SCR 555, in which the claim at issue was as follows:
17. An electrocardiograph cream for use with skin contact electrodes and compatible with normal skin, comprising a stable aqueous emulsion that is anionic, cationic or non-ionic and, containing sufficient highly ionizable salt to provide good electrical conductivity.
The defendants argued that the claim was invalid because it encompassed combinations which are toxic or otherwise incompatible with the normal human skin, notwithstanding that no person skilled in the art would think of using such substances (562). The SCC rejected this argument, holding that properly construed, the claim encompassed only creams that are compatible with normal human skin (563).
With respect, I cannot agree that Claim 17 is invalid because the words "compatible with normal skin" are found before "comprising" instead of after, so that it would be valid, it seems, if the words were rearranged as follows:
17. An electrocardiograph cream for use with skin contact electrodes comprising a stable aqueous emulsion that is anionic, cationic or non-ionic, containing sufficient highly ionizable salt to provide good electrical conductivity and compatible with normal skin.
But is it essential to the holding that the words “compatible with normal skin” appear in the claim itself? If so, the Locke J’s DOVOBET holding is distinguishable, because no similar express limitation appears in Claim 17, which specifies only that the formulation is "for dermal use".
The SCC holding in Burton Parsons might be read as turning on those express words, but it can also be read more broadly, as in the following passage:
To [a person skilled in the art] it must be obvious that a cream for use with skin contact electrodes is not to be made up with ingredients that are toxic or irritating, or are apt to stain or discolour the skin.
This suggests that because a skilled person would know the invention is for medical use, the skilled person would appreciate it cannot be toxic, even if that is not stated expressly. That is essentially Locke J’s reasoning. But then the SCC went on to say:
The man skilled in the art will just as well appreciate this necessity if the cream to be made is described as "compatible with normal skin" as if it is described as containing only ingredients compatible with normal skin.
This could be taken as qualifying the previous statement, and requiring explicit words in the claim; or it could simply be an elaboration based on the particular facts of the case. It seems to me that the reason a skilled person would not be misled whether the words “compatible with normal skin” were the beginning or the end because they would be reading it in light of their knowledge that the cream has to be safe for human use. If that is true, then surely it is also true that a skilled person would know that whether or not the claim said so expressly, as Locke J held. This interpretation is strongly supported by the SCC’s statement that:
the avoidance of unsuitable salts due to their known noxious properties is similarly nothing but the application of the proper knowledge to be expected from a man skilled in the art. In Sandoz Patents Ltd. v. Gilcross Ltd., we had no hesitation in upholding claims for “therapeutically tolerable salts” of thioridazine to be obtained by reacting “with a therapeutically acceptable acid”. I cannot think that the omission of the qualification “therapeutically acceptable” would have voided the patent . . . .
If that is right, then Minerals Separation was wrongly decided. The SCC distinguished Minerals Separation by saying “The inutility of cellulose xanthate in Minerals Separation. . . was not known to the prior art” (564). But if that were the true distinction, then any claim using “comprising” language would still be invalid, so long as we can find a Compound X that was only discovered to be poisonous after the publication date, even if it would be obvious to a skilled person that it was poisonous and should not be used. There is still a technical distinction to be made, as in that hypothetical case the noxious properties would not be “known” as of the date of publication. But I would have thought a skilled person would interpret the claim to exclude all noxious substances, not a (very long) list of specific substances known to be noxious as of the date of publication. Moreover, that technical distinction is not consistent with the SCC’s following exhortation that
It does not seem to me that inventors are to be looked upon as Shylock claiming his pound of flesh. In the present case, there was admittedly a meritorious invention and [the defendant] was in no way misled as to the true nature of the disclosure nor as to the proper methods of making a competing cream.
This is essentially an exhortation to use a purposive construction rather than the “meticulous verbal analysis” which was subsequently disparaged in Catnic. Whether the poisonous Compound X is discovered before or after the publication date of the patent, a person skilled in the art would know not to use it in a medical cream. While the SCC distinguished Minerals Separation rather than rejecting it, the distinction is not convincing, and the approach to claim construction adopted in Burton Parsons – essentially the modern purposive approach – is inconsistent with technical approach used in Minerals Separation.
To summarize, in my view Locke J was right for the reasons he gave, and it is time to acknowledge that the JCPC holding in Minerals Separation was wrong.