ADHD Drug Patent Held to Cover All Salt Forms

Does a patent whose claims specify two particular salt forms of a pharmaceutical compound prevent competitors from launching other salt forms? The Patent and Market Court of Appeal (PMÖD) recently answered in the affirmative, further holding that it was immaterial that the patent could only be granted after the holder had narrowed claims originally covering all pharmaceutically acceptable salts.

A patent’s scope of protection is determined by its claims, read in light of the description, and may extend beyond their literal wording to cover equivalents – embodiments that exploit the inventive concept and produce functionally equivalent results. Swedish case law has established a test for equivalence while also recognising circumstances that may preclude such extension, including where the equivalent formed part of the prior art at the priority date or where the patent holder made statements during prosecution amounting to a surrender of protection for certain embodiments.

For a patent to be granted, the invention must be novel, involve an inventive step, and the claims must have basis in the application as originally filed. The last of these requirements is designed to prevent an applicant from gaining an unjustified competitive advantage by amending the claims after filing. The standard is therefore rather strict: an amendment is only permissible if the resulting subject matter is directly and unambiguously derivable (either explicitly or implicitly) from the original application. This sometimes compels patent holders to limit their claims during prosecution. It has long been unclear whether, and how, such limitations affect the scope for applying the doctrine of equivalents in subsequent infringement proceedings.

The Patent and Market Court (PMD) confronted this question in what were known as the pemetrexed decisions in 2018 and 2020. The patent in question concerned a combination therapy in which the cancer drug pemetrexed was administered together with vitamin B12 to reduce the side effects of pemetrexed. In order to ensure that the claims had basis in the original application, the patent holder had limited the claims to specify only one particular salt of pemetrexed, namely pemetrexed disodium. The issue in those cases was whether a combination using a different salt form (the tromethamine salt) of pemetrexed fell within the scope of protection. PMD held that limitations carried out to satisfy the basis requirement did not preclude a finding of equivalence and accordingly found that infringement had been established.

Regrettably, PMD’s pemetrexed judgments were never appealed to PMÖD, leaving the question without appellate authority.

That opportunity arose in a case concerning the ADHD drug lisdexamfetamine. The patent holder initially obtained a patent covering lisdexamfetamine and (all) its pharmaceutically acceptable salts. Following opposition and appeal proceedings before the EPO, the patent holder was required to limit the claims to three specific forms of lisdexamfetamine (the free base form together with the mesylate and hydrochloride salts) in order to satisfy the basis requirement. A new version of the patent (known as a B2 version) reflecting the amended wording was published following those proceedings.

After the B2 version of the patent was published, a generic pharmaceutical company brought a declaratory action for non-infringement in Sweden. The generic company intended to launch a third salt of lisdexamfetamine (the adipate salt) and sought a declaration that this salt did not infringe the patent. The company acknowledged that the adipate salt exploited the same inventive concept and produced functionally equivalent results but argued that the limitation of the patent precluded a finding of equivalence. The company submitted that the basis requirement served to protect the legal certainty of third parties, and that this purpose would be defeated if embodiments that had been excluded from the patent in order to meet the basis requirement were nevertheless held to constitute infringement.

PMÖD agreed that one purpose of the basis requirement is to safeguard the legal certainty of third parties. Notwithstanding this, PMÖD did not consider that the limitation precluded a finding of equivalence. According to PMÖD, there is a crucial distinction between a situation in which the claims have been limited in order to satisfy the requirements of novelty and inventive step on the one hand, and a situation in which the limitation has been carried out to satisfy the basis requirement on the other. In the latter situation – unlike in the former – PMÖD held that it generally cannot be assumed that the patent holder intended to limit the scope of protection or to surrender protection for embodiments other than those specified in the claims. PMÖD’s reasoning thus indicates that the patent holder’s subjective intent is of decisive importance.

On the question of whether an embodiment once deemed non-derivable from the application as filed can nonetheless fall within the scope of protection of the same patent, PMÖD expressly endorsed the view that the basis examination – which does not take equivalents into account – is stricter than the assessment conducted in infringement proceedings. While PMÖD did not expressly base its decision on this particular reasoning, the court’s endorsement of the distinction between the basis examination and the infringement assessment provides support for the underlying logic: since the EPO never assessed whether the excluded embodiments were equivalent, the exclusion cannot be taken to mean that the patent holder surrendered protection for equivalent embodiments.

In the judgment, handed down in March 2026, PMÖD accordingly held that the adipate salt would constitute infringement of the patent in dispute.

However, PMÖD did not take an entirely definitive position in the lisdexamfetamine case: the court granted leave to appeal to the Supreme Court (HD), recognising the importance of the issues for the development of the law. Regrettably, the judgment was not appealed, most likely because the patent’s term would have expired before a ruling could be expected.

PMÖD’s decision to grant leave to appeal suggests that the last word may not yet have been spoken on how claim limitations affect the scope for applying the doctrine of equivalents.

Nor has the last word been spoken on the lisdexamfetamine patent itself. Several parallel cases are pending concerning the validity of the supplementary protection certificate (SPC) granted on the basis of the patent. PMÖD has granted leave to appeal in a Swedish invalidity case, and in parallel Danish proceedings, the court has referred questions to the Court of Justice of the European Union (CJEU) seeking guidance on supplementary protection for prodrugs of previously known active substances.

Setterwalls is monitoring these developments and expects to provide a further update once the CJEU has delivered its preliminary ruling.