Recent reports have found that, when used together, there is an apparent interaction between the two medications which causes an increased likelihood of an ivermectin toxicity, similar to an ivermectin overdose, in dogs. Adverse reactions can cause a range of symptoms, from ‘Collie nose’ to a full blown toxicity with neurological signs of ataxia, drooling, vomiting and pupil dilation. At its most severe, the reaction can lead to a coma.

Ivermectin is a drug used in a wide range of treatments for heartworm prevention, including the popular Heartgard and Advocate products, as well in readily available products for the treatment of mange and other conditions. Although Comfortis is not an ivermectin-based product it can apparently create an increased chance of adverse reactions if used at the same time as some products containing ivermection.

Until more data is available, we are advising our clients that Comfortis is safe to use with the Proheart annual injection for heartworm but should not be used in conjunction with other ivermectin-based products.

Although we are able to ensure our regular clients are aware of the dangers, many ivermectin-based products are also available in supermarkets and pet stores, who may be unaware of the risks. If you are using any ivermectin products, and also using an ivermectin-based products, please tell us. If you are unsure, please call the hospital for advice; our nurses are fully informed about the issue.

We would also urge you to advise any of your dog-loving friends who may use these flea and heartworm protection medications to check with us, or their own vet.