A recent judgement of the English Patents Court has shed light on the assessment of priority (Hospira UK Limited v Cubist Pharmaceuticals LLC  EWHC 1285 (Pat)). The guidance relates to the requirement that a European application enjoys a right of priority from an earlier application only if it is in respect of the “same invention” (Article 87(1)(b) EPC). The relevant Patent in this case had already been the subject of an EPO Opposition Division decision (currently under appeal), thus allowing a direct comparison to be made between the approaches taken by the English Patents Court and the EPO. Whilst, as expected, both follow the test defined by the EPO’s Enlarged Board of Appeal in G2/98, the English Patents Court appears to favour an interpretation of this test that goes beyond a purely formulaic analysis.
In this case, the Claimant (Hospira) sought revocation of three patents owned by the Defendant (Cubist). All three patents concern the antibiotic daptomycin. These patents included EP 1,115,417 (the “Patent”) which has a first claimed priority date of 25 September 1998 and a second claimed priority date of 24 March 1999. In both the English and EPO proceedings, the first priority claim was held invalid, whereas the second priority claim was held to be valid. The consequence of the loss of the first priority claim was that the Patent was held invalid for lack of inventive step over a press release by Cubist on 1 March 1999. Despite the fact that both the English Patents Court and EPO Opposition Division arrived at the same decision, the reasoning provided in each case does highlight a difference between their approaches.
In providing the legal principles to be applied in respect of entitlement to priority, the Judge in the English Patents Court referred to the summary provided by Kitchen LJ in MedImmune Ltd v Novartis Pharmaceuticals UK Ltd.  EWCA Civ 1234. In this judgement of the Court of Appeal, Kitchen LJ referred to G2/98, in which it was held that priority is to be acknowledged only if:
“the person skilled in the art can derive the subject-matter of the claim directly and unambiguously, using common general knowledge, from the previous application as a whole.”
However, Kitchen LJ also noted that:
“The approach is not formulaic: priority is a question about technical disclosure, explicit or implicit. Is there enough in the priority document to give the skilled man essentially the same information as forms the subject of the claim and enables him to work the invention in accordance with that claim.”
In its submissions, Cubist argued that entitlement to priority is a matter of substance and not form, and that the question is whether “the same crux of the invention” or the “key concept” is disclosed in the priority document. Furthermore, Cubist submitted that when a dosage range is disclosed, there is disclosure of a sub-range within that range. Therefore, any selection of a sub-range is entitled to priority unless it constitutes a selection invention over the disclosure of the priority document.
In rejecting the arguments put forward by Cubist, the Judge reiterated that the “test in each case is whether the skilled person can derive the subject matter of the claim directly and unambiguously, using common general knowledge, from the priority document as a whole”. Nevertheless, in assessing the claim to priority, he went beyond the strictly formulaic analysis which tends to be favoured by the EPO.
The Patent at issue is based on medical use claims directed to a dosage regimen for daptomycin of 3-10 mg/kg administered once every 24 hours for treating a bacterial infection. The first priority document (P1) discloses the use of daptomycin in dogs at a dose of 2-10 mg/kg with the same dose re-administered at intervals between 12 and 24 hours. The lower limit of the range claimed in the Patent (i.e. 3 mg/kg) is not mentioned at all in P1. Nevertheless, Cubist argued that the Patent was entitled to the first priority date because the claimed range of 3-10 mg/kg is not a novel selection of the range of 2-10 mg/kg disclosed in P1. Therefore, the two ranges were alleged to be the “same invention”.
In concluding that the first priority claim was invalid, the Opposition Division held that G2/98 requires a strict and narrow interpretation of the “same invention” equating to “the same subject matter”. Applying this interpretation to the feature “3-10 mg/kg”, the Opposition Division noted that, in the absence of any disclosure of a dose of 3 mg/kg, it cannot be concluded that the skilled person would have directly derived the lower end-point of the claimed range from P1. In addition, even if this dose could have been derived, the skilled person could not have done this unambiguously because, in view of the disclosure of the range of 2-10 mg/kg, the dose of 1 mg/kg would logically be equally suitable as the lower end point.
The Judge in the English Patents Court case noted that he agreed with the reasoning of the Opposition Division. However, he also provided additional reasons why the “same invention” is not disclosed in P1. This included highlighting the fact that P1 does not disclose the same dosing interval as claimed in the Patent i.e. it does not disclose administration of the dose once every 24 hours but instead discloses administration at intervals of between 12 and 24 hours.
More significantly the Judge went beyond the “formulaic approach” of the EPO Opposition Division and assessed the effects of the differences. In so doing he concluded that the differences between the dosing ranges and intervals claimed in the Patent and those disclosed in P1 result in a “substantively different invention”. In support of this he noted that “differences in the dose used is important to efficacy and toxicity, and…differences in the dosing interval are significant to toxicity”. The substantive nature of this analysis raises the following question: had it been concluded that the differences did not have a significant effect on the invention, would the decision on priority have been different?