Revolution (which contains the active ingredient Selamectin) is a topical medication that is used for flea and heartworm prevention. While the product has been tested and is safe, some cats may experience a reaction to it where their immune system will overreact to an element of the medication, leading to allergy symptoms. While symptoms in cases of a reaction are usually mild, it is important to seek medical attention should you notice a reaction after administering the medication in order to ensure the best outcome for your cat.

When a cat is experiencing an allergic reaction to Revolution, it is the result of their immune system overreacting to an element of the medication upon it having contact with their skin or being ingested.

Symptoms of an allergy to Revolution are similar to those of other allergies. These include:

It is worth mentioning that if a cat manages to lick any spot-on, drooling will usually occur. We see this often when the spot-on was applied too far down the back or when a litter of kittens was treated and are grooming each other. This is a short-lived reaction to the foul taste and not usually a sign of an allergy. Give your kitty something to eat and drink and monitor them closely.

Medications to prevent fleas and heartworms in your cat are typically available in topical and ingestible forms. The topical medications will be applied to the back of your cat’s neck on his skin, where it cannot be licked off. Should your cat experience an allergy, it can present itself right away or within a few hours or days. The topical form of the medication will be administered to your cat once a month to prevent flea and heartworm infestation. Other products that protect your cat against fleas and heartworms include:

The active drug in Revolution is selamectin. Revolution has been tested in studies using ten times the recommended amount without negative reactions occurring, however, an allergy or negative reaction, while rare, is possible. An allergy to Revolution occurs when the mast cells of your cat’s immune system mount an aggressive response to one of the components of the medication. The mast cells release histamine which will lead to inflammation in the tissues it comes in contact with as they attempt to fight what they see as an intruder. The histamine that is released leads to the allergy symptoms your cat experiences.

Should you notice concerning symptoms in your cat after applying Revolution, you will want to take him to your veterinarian. After conducting a full physical examination, your veterinarian will ask you for information in regards to the symptoms you have noticed, when you first saw them and any changes you have observed. The skin symptoms your cat is experiencing may lead to your veterinarian analysing the affected skin so that he can view cells under a microscope to see if there are any parasites, yeast or bacteria present. Once those are ruled out, your veterinarian will consider other possible causes of your cat’s symptoms.

A complete blood count and chemistry panel may be run; should a specific white blood cell level (eosinophils)  be high it will point to an allergy being present in your cat. The results of the blood work will help eliminate other causes of the symptoms your cat is experiencing. Should your cat be experiencing respiratory problems, a radiograph may be taken so that your veterinarian can view his lungs and rule out illnesses like pneumonia or bronchitis.

Your veterinarian will likely ask you for information about the diet of your cat as well as any supplements and medications that he takes. Be sure to mention when you administered Revolution to your cat as this may help your veterinarian pinpoint the cause of his symptoms.

Your cat’s treatment will depend on the symptoms he is experiencing. Should your cat be experiencing breathing difficulties, these will be addressed immediately with oxygen therapy as appropriate. An antihistamine will likely be administered to decrease the inflammation your cat is experiencing. Unfortunately, antihistamines are not effective in all cats, so this may or may not impact your cat’s condition. The antihistamine may help with any respiratory system swelling as well as skin inflammation. Should your cat be experiencing skin symptoms, shampoos and topical ointments containing hydrocortisone may be recommended to give him immediate relief. 

Corticosteroids (either injected or administered orally) are often very helpful though they can have a range of side effects when used over a long period of time. Should your veterinarian recommend corticosteroids, he will usually plan to monitor your cat’s blood chemistry levels to catch any potential issues as a result of the medication. If your cat develops a secondary bacterial infection due to their excessive licking and scratching, an antibiotic will be prescribed.

You will want to work closely with your veterinarian to ensure the best outcome for your cat. Should your cat react to Revolution, you will want to avoid giving it to him in the future. Fortunately, there are other options for flea and heartworm prevention for your cat and you can choose one of those for his protection. Your veterinarian may recommend follow-up appointments so that he can see how your cat is doing and make any necessary changes to his treatment plan.