Dogs, as their human counterparts, develop allergies to many different types of allergens, such as dust, pollen and foods. In most dogs, allergies are likely to crop up while they're under 3 years old, though some dogs will develop new allergies around age 6. And like us, dogs can take an antihistamine to counteract the symptoms. However, it's important to remember that antihistamines don't cure the allergy, they simply treat the symptoms.
Antihistamine Uses in Dogs
Antihistamines are used to treat many of the same allergy symptoms in dogs as in humans. The symptoms most commonly noticed in dogs with allergies include sneezing, reverse sneezing (sucking air in to clear debris from the nose), gagging and itchiness. It's important to note that dogs with food allergies may not present these symptoms, but will vomit instead. In those cases, antihistamines are not appropriate.
Types of Antihistamines
There are four types of antihistamines: diphenhydramine, hydroxyzine, clemastine fumarate and chlorpheniramine. Diphenhydramine is the most commonly recommended antihistamine for dogs in the form of over-the-counter benadryl. Clemastine fumarate, which is the generic drug Tavist, is highly recommended to reduce swelling and itchiness in dogs. Though those two are frequently recommended, your vet may want to try your dog on each of the four antihistamines. Usually these tests are conducted for a period of two weeks each, and at the end of the tests, your vet should be able to help you determine which was the most effective at treating your dog's specific allergy symptoms.
In general, the recommended dose of an antihistamine is one milligram per pound every 12 hours. However, when first administering an antihistamine, start with a smaller amount to gauge how your dog will react to the new medication.
Side effects of antihistamines can include drowsiness, lethargy and nausea. It's wise to start your dog on a smaller dose to determine how severely he will react to the medication. In some cases, if your dog is particularly itchy and is causing himself harm (like scratching himself until he bleeds), drowsiness may not be an adverse side effect.
Though an antihistamine can alleviate a dog's worst allergy symptoms, some dogs can have a severe reaction, including seizures. If you are unsure about your dog's reaction, consult a vet or try a non-medication approach, like an oatmeal bath, rubbing aloe vera into your dog's coat or even adding fatty acids to his food.