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My boxer has skin allergy and the vet advised said to give him two Benadryl tablets, once in the morning and again at night. They don't seem to be working anymore, after more than two years. Any advice?

Itchiness, referred to as pruritus, can be a challenge to control when caused by allergies. Allergic symptoms often grow more severe with time. Animals who initially had symptoms only at certain times of the year may show discomfort for longer periods as they age until they seem to be uncomfortable year round. Ideally the substances causing the dog's allergies, called allergens, are identified using skin tests or what are known as elimination diets in those suspected of having food allergies. There are also some blood tests that may be helpful in obtaining this information and are often the better alternative in cats in whom skin testing is frequently unreliable. These allergens are then eliminated from the animal's environment, or if that's impossible, allergy vaccines can be prepared to desensitize the patient. When testing is impractical or inconclusive, a number of strategies are employed in efforts to give these patients relief. The most consistently reliable results are achieved with the use of cortisone or related drugs. Unfortunately the long term use of these medications is limited by their side effects which include increased thirst and urination, immune system suppression, muscle wasting, and the development of diabetes. Antihistamines such as benadryl are less predictable in their results and several compounds representing different classes of these drugs may need to be tried before finding one that helps a particular patient. Sometimes none is effective. At other times a histamine will only help to the extent that it permits a reduction in the dose of cortisone required to reduce the animal's symptoms to an acceptable level. Equally or more important than the use of systemic, i.e. oral, medications in the control of pruritus is the use of topical medications found in a number of shampoos and sprays. These can contain antihistamines, emolllients, oatmeal, or other substances which can be quite effective in providing relief to these animals when properly applied. Baths should be given in lukewarm to cool water and the shampoo allowed to remain in contact with the animal's skin for fifteen minutes after which it must be thoroughly rinsed off. Your veterinarian can design a plan to rationally test the variety of oral and topical medications used to make allergic animals more comfortable.

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