Chronic Atopic Dermatitis

Management of Dogs with Chronic Atopic Dermatitis: What’s New?
Rosanna Marsella, DVM, DACVD

University of Florida

Concept of pruritic threshold and co-factors involved in the pathogenesis of atopic dermatitis (AD) According to the theory of threshold a given individual can tolerate a variety of stimuli without developing clinical signs as long as the threshold is not reached. All these stimuli have an additive effect and once the threshold is reached itching and other clinical signs become evident
Most dogs with AD also have other allergies thus control of concurrent allergies is crucial to decrease the severity of clinical signs.
Dogs with AD are prone to secondary skin infections that significantly contribute to the level of discomfort. Resolution of skin infections may dramatically decrease the level of pruritus.
For severe cases or for cases with clinical signs all year round, Immunotherapy (IT) is the best long-term therapy.
IT is effective in 60 to 80 percent of cases and is especially indicated in young animals. Vaccine should be made including the positive results of the allergy test.
Choice of allergens is based on the history of each case (e.g. seasonality, plants are more prevalent in the patient’s environment).
More than one vaccine may be necessary in cases with numerous allergies.
Side effects are not common and include increased pruritus after the injection, urticaria, and rarely anaphylaxis.
Response to IT is not usually evident of the first three to four months and it may take up to a full year before full efficacy is evaluated. If adverse effects are seen, schedule may need to be adjusted. It might be useful to pre-medicate the patient with antihistamines one hour before the injection.
Once the maintenance dose is achieved the interval of administration is judged based on the individual case.

Pharmacotherapy: New Therapies

Cyclosporine A (CsA) is very effective in severe cases of AD. In one study, CsA was administered PO to the dogs at 10-20 mgkg-1 and decrease of pruritus was evident within a few days. After remission was noted, the dose was tapered to the lowest every other day dose.
In another study, Cs was given orally SID at 5 mgkg-1 for six weeks. At the end of trial, pruritus decreased by 78 percent according to owners and skin lesions decreased by 58 percent according to the investigator. No difference in efficacy was noted between prednisolone and CS therapy.

CsA is available in capsules (25 and 100 mg) or in an oral solution (100mg/ml). CsA is fairly pricey (1 bottle of 50 ml oral solution costs around $300 and 30 capsules of 100 mg cost from $170-$190).
Soft gel capsules (Sandimmune®) and microemulsion formulations (Neoral®) are not  interchangeable with the latter having a higher bioavailability. Studies reported for canine AD utilized the microemulsion formulation.

Misoprostol (Cytotec®, Searle, Skolkie, IL, USA) is a PGE1 analog with anti-allergic properties.
In an open study of 20 dogs with AD, significant improvement was detected when misoprostol was given at 3-6 mcgkg-1 TID for 30 days. Pruritus decreased by half in 56 percent of the dogs and skin lesions improved similarly in 61 percent of cases. Improvement was seen after one week of administration. Adverse effects consisted in mild vomiting and diarrhea in some patients.
In another blinded, placebo-controlled trial 20 dogs with AD were given either three weeks of placebo of misoprostol at 5 mcgkg-1 orally TID. Both pruritus and skin lesions significantly improved. Misoprostol may be combined with antihistamines to improve efficacy and decrease the need for glucocorticoids.

Pentoxifylline (PTX)

PTX, Trental® (Hoechst-Russel Pharmaceutics, Trenton, NJ, USA) is a phosphodiesterase inhibitor that has multiple immunomodulatory properties.
PTX (10mgkg-1 BID) has been used for canine AD in a double-blinded, placebo controlled, clinical trial for four weeks. Clinical signs were evaluated and scored by investigator and owners. During PTX treatment, both pruritus and skin lesions improved significantly but not resolved completely. No adverse effects were reported.

Dog Owners and Breeders Symposium
July 28, 2001
University of Florida
College of Veterinary Medicine