AC is a biocidal active substance that is used in rodenticide baits to control mice. AC has also been used as an avicide and an anaesthetic in clinical practice for human, feline and canine patients as well as laboratory animals, however it is currently not used clinically (1).
For many years the anticoagulants have dominated the Nordic market for control of mice. Based on their reproductive toxicity properties, all anticoagulants meet the exclusion criterion under the Biocidal Products Regulation (BPR – (EU) No 528/2012). Additionally, the 2nd generation anticoagulants meet the exclusion criterion because they are PBT (persistent, bioaccumulative and toxic) or vPvB (very persistent, very bioaccumulating) substances, i.e., they stay in the environment for a long time and accumulate in the food chain. This has led to a strict regulation of these products. AC was approved as a biocidal active substance in 2009 (2009/93/EC) under the Biocidal Product Directive (BPD (98/8/EC) in the European Union, and it has been considered a better alternative than the anticoagulants because it was less persistent and bioaccumulative.
AC containing biocidal products were first authorised for use by both the general public and professionals. As a response to an increased observation of suspected secondary poisoning in cats, the authorisation was restricted to trained professional use only, in Norway by the Norwegian Environment Agency from May 2020 and in Sweden by the Swedish Chemicals Agency (KEMI) from December 2019. In Finland restriction to trained professional use by the Finnish Safety and Chemicals Agency (Tukes) was appealed in December 2021 by the authorisation holders and thus the restrictions are not legally valid (the court case is in progress when finalising this report). In Denmark the products are authorised by the Danish EPA for both professional and public use, but they are restricted to use in bait boxes.
The marked increase in suspected cases of AC-poisoning in cats mentioned above, was reported to national veterinary and chemical authorities and institutes in Finland, Norway and Sweden in 2018 and 2019 by veterinarians working in clinical practices in the respective countries (1,2). This is exemplified by the graph showing annually suspected AC-poisoning cases at the University Animal Hospital, Small Animal Clinic in Uppsala in fig 1, reproduced by permission from the publication by Tegner et al. (2). The medical history led several veterinarians to suspect that the cats were poisoned secondarily from eating poisoned mice (1). The increase in cases led to concern among cat owners, and also received attention in the media (fig 2). The same concern was not reported from Danish chemical authorities, but the Danish EPA have conducted an informal survey where they received a small number of suspected AC-poisoning cases of cats and one dog (personal communication, Jesper Johannesen, Danish EPA).