Comfortis is a useful insecticide based on spinosad, a substance derived from soil microbes. While studies have shown the incidence of severe reactions to be low, there are still some reports of serious side effects from owners. Existing medical conditions and mixing the substance with other drugs or supplements can increase the chances of a bad reaction. Known contraindications and interactions are listed below.

Medical Conditions

There is not yet much information on the contraindications of this medicine. However, you may not want to give spinosad to dogs who are especially prone to seizures as seizing has been noted as a side effect in these cases. It may also be unsuitable for dogs with an allergy to pork, as the flavoring is created using pork-based proteins. Comfortis should not be given to pregnant animals due to its likelihood of inducing abortion.


Spinosad is a PgP substrate, which means it could potentially interact with other PgP substrates such as doxorubicin and digoxin. There is also the possibility for an interaction between Comfortis and ivermectin. When ivermectin is used in conjunction with spinosad, and at the higher doses often used for the treatment of mange, there is a significantly increased risk of negative side effects. Never give spinosad to dogs who have previously suffered bad reactions to it.

I Just Gave Comfortis To An Unsuitable Dog!

If you’ve given Comfortis to a dog who you feel may be unsuitable for treatment watch them closely for signs of a bad reaction. Pet owners with seizure-prone dogs needn’t worry as much, as seizure incidence is still relatively low when spinosad is given to sensitive dogs. However, owners who have accidentally used Comfortis in conjunction with ivermectin should be wary of symptoms including tremors, seizures, drooling, disorientation, loss of sight and difficulty standing up. It’s recommended that you call your vet immediately in cases where you accidentally mix the two drugs and in any case where your pet suffers a serious reaction.

Emergency: If you administer an overdose by mistake or if your dog gains access to and eats an overdose of pills, you should seek help by ringing your vet or the Pet Poison Helpline on 800-213-6680 (US).