Since the extent of protection conferred by a European patent is determined by the claims [Art. 69(1) EPC], it is of utmost importance to draft the claims on the basis of working embodiments of the invention as broadly as possible, but without running the risk of conflicting with the enablement and support requirement of Art. 83 EPC. 

A rather tricky situation may arise in the field of patenting compounds for medical purposes, where protection of compounds in the so-called first medical use claim format “compound X for use in medicine” or “compound X for use as a medicament” is considered as in line with the requirement of Art. 83 EPC if at least some medical use has been shown or is plausible, while the formulation as a so-called second medical use claim “compound X for use in the treatment of a disease from the list of diseases Y, Z, etc.” may face an enablement objection under Art. 83 EPC if the therapeutic effect has not been shown or is not plausible for all claimed diseases Y, Z, etc. In other words, if a therapeutic effect of a compound has been shown for the first time, in view of Art. 83 EPC a second medical use claim may be attacked or even annihilated in opposition or invalidity proceedings by third persons more easily than a first medical use claim. This is irritating in that the first medical use claim is more valuable in terms of scope of protection as it covers any medical use, including the use for the treatment of diseases Y, Z, etc. as defined in the second medical use claim format. 

Recent EPO’s Board of Appeal decision in case T 2627/17 of January 25, 2022 illustrates this tricky situation. In said case, the patent was concerned with compounds to treat, prevent or diagnose diseases that involve estrogen receptor activity. In the application as filed, biological activity data were provided for exemplarily compounds which were considered sufficient to support the first medical use claim specifying the intended use as being “for use in medicine”. Consequently, the board found the first medical use claim to be sufficiently enabled in terms of Art. 83 EPC. However, the board came to a different conclusion for the second medical use claim directed to the same compounds but with the specific second medical use claim wording “for use in the treatment of …(list of diseases, including for example, alcoholism, migraine, cirrhosis, hepatitis B, chronic liver disease, bone density, obesity, migraine, ADHD, dementia, major depressive disorder and psychosis)”. For a number of said diseases there was no verifiable technical evidence of any link to the estrogen receptor, and therefore the board assumed that the therapeutic effects could not be achieved for those diseases. In conclusion, the board considered the second medical use claim as insufficiently enabled under Art. 83 EPC.

The guidance is therefore quite clear: when a therapeutic use of a compound has been shown for the first time, it is definitely worth claiming this specific use not only in the format of a second medical use claim, but also using the first medical use claim format (“compound X for use in medicine” or “compound X for use as a medicament”) as a valid option with an even broader scope of protection and unlikely problems with regard to Art. 83 EPC.