Atopic dermatitis: Why topical therapy is worth a try

Steve / stock.adobe.comAtopic dermatitis is commonly encountered in small animal general practice. Management is often lifelong and can be frustrating for both the veterinarian and client. Many successful treatment plans require a combination of therapies, including (among other modalities) antipruritic, antibacterial and antifungal agents. While many of these therapies are administered systemically, topical therapies are being used with increasing frequency. At the Fetch dvm360 conference in San Diego, Laura Wilson, DVM, DACVD, discussed the use of topical therapies in atopic dermatitis.

Pathophysiologic considerations

The pathophysiology of atopic dermatitis is multifactorial, and our understanding is continually evolving, said Dr. Wilson, who practices at Advanced Veterinary Specialty Group in Tustin, California. One of the most important pathophysiologic considerations when using topical therapy is the presence of a defective epidermal barrier. This defective barrier allows penetration of allergens and antigens through the stratum corneum, where they contact antigen-presenting cells and stimulate an inflammatory response. Supporting restoration of epidermal barrier function should be a consideration when treating atopic dogs.

Goals of topical therapy

Topical therapies are used most often as an adjunct to systemic therapy. Only in rare cases (e.g. mild sebaceous adenitis, secondary superficial pyoderma) are they used as the sole therapeutic agent.

The primary goal of topical therapy is to reduce the use of systemic medications, which may elicit more adverse effects, especially with long-term use. Other goals include restoration and support of normal epithelial barrier function and reduction of the long-term financial burden of atopic dermatitis treatment. This is achieved by helping to better control pruritus and secondary infections, minimizing the need for future visits.

Principles of topical therapy

Before instituting topical therapy, a definitive diagnosis should be obtained through a complete dermatology workup that includes history, physical examination, cytology and advanced diagnostics when indicated. Additionally, it is important for the veterinarian to be familiar with various product formulations so that the best medications are selected, the vehicle is appropriate, and potential adverse effects can be discussed with the owner.

Dr. Wilson encouraged practitioners to use topical therapies judiciously because these medications are not without risk. Even though the application is topical, systemic absorption will occur and is increased in the presence of elevated temperatures and dermal blood flow. Iatrogenic hyperadrenocorticism has been reported with long-term use of topical steroids.

Additionally, some topical products may cause a local reaction that can worsen the patient's condition. These reactions may be due to ingredients that are drying or irritating or to the presence of perfumes or dyes. The skin of atopic patients is often more sensitive than that of their normal counterparts, and this may necessitate avoiding products not designed for pets; human shampoos, for example, have a different pH level than that of pet-specific shampoos.

Because compliance is the most common barrier to successful topical therapy, Dr. Wilson recommends careful client and patient selection. In cases where compliance is in doubt, systemic therapies should be prioritized. Prescription shampoo products are unlikely to be effective when owners will not follow instructions to bathe their pet regularly or for patients that are fearful. In other cases, patients may groom or lick off topical medications, minimizing their efficacy. In addition, topical therapy may be cost-prohibitive for some clients and is time- and labor-intensive.

Shampoos

The most common type of topical therapy employed in the treatment of atopic dermatitis is a prescription shampoo. These products are formulated to contain different amounts and types of antipruritic, antibiotic, antifungal, anti-seborrheic or antiparasitic medications. Most prescription shampoos are also formulated with special molecules that may increase the duration of action of medications, help strengthen epidermal barrier function, or have additional antimicrobial properties, such as phytosphingosine, spherulites, and novosomes. The type and mechanism of action of these molecules vary by manufacturer.

Tips for improving compliance with prescription shampoos

Select a shampoo based on thorough patient evaluation and diagnosis of underlying conditions and secondary infections.

Advise owners to bathe the pet with lukewarm or cool water as hot water can increase the feeling of pruritus.

Discuss the importance of appropriate contact time (generally eight to 10 minutes) and offer suggestions for ways to occupy that time, such as walking the dog around outside while waiting for the contact time to lapse.

For patients with dirty or greasy haircoats and skin, multiple rounds of shampooing may be required, as grease and dirt will decrease lather. Consider asking clients to bathe the pet initially with an over-the-counter pet shampoo to degrease and clean the skin and haircoat, then repeat with the medicated product to minimize the amount of the more expensive product used for each bath.

Explain to owners that medicated shampoos will not lather as much as nonmedicated shampoos. Clients who expect a large amount of lather are more likely to overuse the product and run out of the shampoo more quickly, which can lead to frustration and extra expense for the owner.

Other topical therapies

Numerous other formulations of topical therapeutics are available for pets with atopic dermatitis, including wipes, sprays, mousses, lotions, soaks, rinses, gels and ointments. These formulations often contain similar ingredients to shampoos but may be used for more focal disease. Products such as mousses or wipes may be easier for clients to apply than shampoos and this may increase compliance. Gels, ointments, creams and lotions are best used on nonhaired skin such as skin folds, interdigital spaces and ears. It is important to remember that hair functions as a natural barrier and may need to be clipped to help facilitate delivery of the topical medication to the site requiring treatment.

Conclusion

Topical therapies can be a useful adjunct for many cases of atopic dermatitis. While the risks of adverse effects are lower than with systemic medication, there remains the potential for adverse events. Dr. Wilson encouraged practitioners to use topical therapies for atopic patients to help reduce the use of systemic medication, but with the caveat that appropriate patient and client selection are essential to success.

Dr. Boatright, a 2013 graduate of the University of Pennsylvania, is an associate veterinarian in western Pennsylvania. She is actively involved in her state and local veterinary medical associations and is a former national officer of the Veterinary Business Management Association.