Some cats develop allergies to medications that are prescribed to them, such as medication to eradicate an ear mite infestation. Contact allergies of all sorts are caused by the aggressive response of specialized immune cells, called mast cells, to an allergen. When an allergen activates the immune system, the immune system then manufactures a protein that causes the release of histamine, a naturally occurring compound that has an inflammatory effect on any tissues that it comes into contact with. In cats, this can cause an uncomfortable and unsightly skin condition that often centers around the head and neck.

Allergies to medications, such as the miticides used to kill ear mites, may leave your pet with an uncomfortable rash and possibly even lesions and should prompt a call to your veterinarian.

Symptoms of allergies in cats are typically exhibited as skin problems, regardless of the type of allergy. Allergy symptoms caused by treating ear mites are likely to be centered on the head and ears of the cat but may show up anywhere on their body. These can include: 

There are two varieties of miticide that are used to treat ear mites. These include: 

This is the main component in the brand names like Ear Miticide and KC Ear Mite drops as well as being used in some flea and tick treatments. It is known to sometimes cause irritation to the skin that it comes in contact with and it can be toxic if ingested. Rotenone is slower-acting but more potent than Pyrethrins, although much of the potency may be lost with exposure to light and oxygen. 

Used more commonly for dogs than for cats as cats can be sensitive to the toxins in the insecticide. The toxins in pyrethrins that are used to kill the invading insects are neurotoxins, and if ingested by the cat they may lead to severe neurological symptoms. It is imperative to follow your veterinarian's instructions when administering these products.

Skin allergies caused by exposure to medications are a result of an overly aggressive response by a specialized type of immune cell known as a mast cell to a protein present in the miticide. Either synthetic or naturally occurring proteins are capable of stimulating the mast cells to release a chemical known as histamine. Histamine’s inflammatory influence is what causes the majority of the itching and swelling that is characteristic of an allergic response.

The signs and symptoms that are indicative of an allergy will generally prompt your cat’s doctor to collect a sample from an affected area using a technique known as skin scraping. The samples acquired will then be evaluated by cutaneous cytology which is an examination of the skin cells using a microscope in order to search for complications such as mites and yeast infections.

When this fails to reveal any other disorders, the cat’s symptoms combined with the timing of the response may help to make a preliminary diagnosis, at which time a patch test, also known as an intradermal skin test, may be recommended. Miniscule amounts of the antigens that the veterinarian suspects, as well as common allergens in the area, are injected under the skin in order to induce a localized reaction. This may include tests for the miticide itself as well as tests to check the allergic response to the mite’s saliva as well. Many veterinary professionals may choose to diagnose the trigger by eliminating suspected allergens from the environment first, in this case, by changing to an alternate treatment for the ear mites.

Either changing the miticide used to treat the ear mite infestation or ceasing miticide treatments entirely will be required for the symptoms to cease, and in many cases, symptoms will continue for a time after the medication has been eliminated. There are a number of antihistamines that are relatively effective for felines; both formulated specifically for cats and some are formulated for humans. It is essential that you never give your pet human medications without the advice and supervision of a veterinarian as even those that are safe to use may require species-specific adjustments to the dosage. Salves and shampoos made with hydrocortisone may also help to relieve skin discomfort, although your pet should be prevented from licking off these preparations.

If neither antihistamines or hydrocortisone preparations are successful in reducing the allergy-related symptoms, then corticosteroid injections or oral tablets may be recommended. Although cats can develop side effects from the corticosteroids, it is much less common than it is for dogs. Although injected immunotherapy is available for allergies to many medications, it is not typically practical for miticide allergies as it takes several months to become effective.

Feline contact allergies can be just as unsightly and uncomfortable for our cats as they are for us and ensuring that treatment is continued can be more than just a cosmetic issue. Secondary skin infections are not uncommon on skin that has been damaged by an allergic reaction, and either topical or oral antibiotics will be required if this occurs. Completing the full measure of antibiotic medication is crucial even if the symptoms appear to have subsided. Discontinuing the medication before the infection has been completely eliminated could cause the infection to reoccur.