Principles of Topical Therapy in Animals
Topical therapy is an important part of veterinary dermatology. It is now recognized as a key component of the management of bacterial and yeast overgrowth (often as the first line of therapy), primary seborrhea, and allergic dermatitis.
The following are some basic guidelines to consider when prescribing topical therapy for a dermatologic condition:
Medicated shampoo products are not "grooming shampoos." The hair coat should be thoroughly combed to remove loose hairs and undercoat. This is often best done by a professional groomer.. Good grooming practices facilitate topical therapy and can significantly help shorten the course of disease.
Topical therapy should not be prescribed if the patient's owner cannot bathe or spray the animal.
Animals should be pre-washed in a cleansing shampoo first to remove debris, then washed in a medicated shampoo. To minimize irritant reactions and enhance delivery and rinsing of the hair coat, the owner should be instructed to predilute the medicated shampoo in a bucket or container. The animal should be fully lathered and the skin and hair coat massaged during the contact time. The animal should never be left standing with lather in a tub shivering. Three to five minutes is effective. Animals should be bathed three times a week.
Animals tend to groom off topical products and may vomit after ingestion. The risk of toxicity is a constant worry for owners. Local ointments, gels, and sprays are best used sparingly, under occlusion, and for specific diseases. Such medications often sting when applied to the skin, especially many of those instilled into the ears. Many agents also may mat the hair.
The animal should be monitored closely for possible development of irritant or allergic contact dermatitis from topical agents. Many topical agents have very similar bases or ingredients, and changing from one to another may only exacerbate the problem.
Owners should be given careful and thorough instructions on how to administer the therapy.
Shampoos are the most commonly used topical treatments. There are three broad classes of shampoos: cleansing, antiparasitic, and medicated. Cleansing shampoos remove dirt and excess oils from the coat. These products include over-the-counter dog grooming shampoos, flea shampoos, and many mild human products. These products lather well and must be rinsed from the coat. Antiparasitic shampoos are “flea shampoos.” In most cases, the amount of insecticide in these products is not adequate to kill all the fleas in a severe infestation. However, these products are excellent routine cleansing products. Medicated shampoos include antimicrobial and antiseborrheic products.
The best choices for antimicrobial shampoos are ones with chlorhexidine combined with miconazole, ketoconazole, or climbazole. Antiseborrheic shampoos contain some combination of tar, sulfur, and salicylic acid—ingredients that are keratoplastic and keratolytic. Tar is recommended for oily seborrhea, and sulfur and salicylic acid are recommended for scaly seborrhea. Most animals benefit from products that contain all three agents; however, tar products are contraindicated in cats.