Topical solutions for allergy, pyoderma and scaling disorders (Proceedings)

When talking about topicals, it is necessary to first understand the basic functions of the skin and how the skin performs these. Then we will further define which topical solutions might work best for each skin condition.

The basic functions of the skin are to hold the moisture in, exclude the pathogens and protect from physical and chemical insults. At the most basic level, the skin does this by 3 mechanisms—the stratum corneum, the lipid film and the natural flora. The stratum corneum is the most exterior of the layers of the epidermis and is very tightly packed. To seal the areas between cells, there is the lipid film. This contains ceramides, long chain free fatty acids and cholesterol. The fatty acids are also antibacterial. The normal skin microflora occupies microbial niches and inhibits colonization of invading organisms. These microorganisms may be described as resident or transient and may change with the environment the host inhabits. There is also continual desquamation of the skin cells which helps to control microbial proliferation.

First, we'll discuss some of the newer approaches to shampoo therapy. Phytosphingosine is a pro-ceramide that is the basis of a newer line of products. It is naturally present in the skin, is antimicrobial and anti-inflammatory. This product is deposited on the hair and works its way to into the sebaceous glands. This is then gradually released with the sebum onto the skin. Another newer approach to shampoo therapy is glycotechnology. With this technology, the exogenous sugars bind to the microbial lectins saturating them so they can not bind to the host carbohydrates. Thus, these sugars theoretically are antimicrobial. Additionally, they are anti-inflammatory since they do not allow binding to the keratinocytes and thus the immune signal production is blocked. Spherulites are another microdelivery system that is basically microvesicles which serve as a delivery system for the encapsulation of active ingredients. This increases the bioavailablity of therapeutic agents and promotes immediate and residual moisturizing properties.

In general shampoos can be used in limited areas or for more generalized conditions. Depending upon the severity and type of condition being treated, shampoos are generally applied 1-2 times per week. They should be in contact with the skin for 5-15 minutes and then the haircoat should be thoroughly washed clean so no residue remains.

For bacterial infections, topical therapy may be adjunctive or can be the sole therapy depending on the severity of the bacterial infections. Generally, the best topical solutions for bacterial infections would include the benzoyl peroxides, chlorhexidine based and ethyl lactate based shampoos. Benzoyl peroxides generally are manufactured in concentrations ranging from 2-3%. Five percent benzoyl peroxide products should not be used in our pets as they are too irritating. They have added effect of being great follicular flushers and thus helping with comedones and demodicosis. However, they can be drying and may bleach fabrics. Chlorhexidine is very effective against most bacteria except some Pseudomonas and Serratia strains. Concentrations range from 0.5-4%. This is well tolerated and not as drying as the benzoyl peroxides. However, it can occasionally cause corneal ulceration and irritation in cats. Chlorhexidine at 0.5 percent has been shown to slow granulation tissue formation so use care and be mindful of concentrations when using as a wound antiseptic in cases where it may have prolonged contact with tissues. Ethyl lactate is a formulation that is hydrolyzed in the skin to ethanol and lactic acid thereby decreasing the pH of the skin and thus is antibacterial. It is also well tolerated. These products are variably available as shampoos, sprays, rinses, gels and medicated wipes/pads.

For fungal infections, there are also a number of ingredients that are very helpful. Ketoconazole, miconazole, chlorhexidine and sulfurs are all good antifungals. For dermatophytosis, the topicals are primarily an adjunctive therapy. Shampoos alone are not usually effective in treating dermatophytosis. Sulfur based rinses which are left on to dry can be quite helpful in the treatment of dermatophytosis, but can stain, are malodorous and certainly aren't easy to do in most of our feline patients. When using the rinses, an E-collar should be applied until the rinse is dry as these rinses can upset the gastrointestinal tracts when licked off.

For Malassezia, topical therapy can be used to aid in the treatment, but also to maintain remission. The most common ingredients and concentrations are miconazole (2%), chlorhexidine (2-4%), combination of both (2% each), ketoconazole (2%), selenium sulfide (1%) or a combination of chlorhexidine (2%) and ketoconazole (1%). These topicals can be most helpful in a shampoo, spray or wipe format. Selenium sulfide shampoos are only available as a human OTC product (Selsun Blue). The side effects are staining, excessive drying and irritation especially to the mucous mumbranes and scrotum. The selenium sulfide shampoo should not be used in cats.

For allergies, shampoos in general are very helpful. This can serve the functions of soothing the skin, rehydrating the skin, helping to normalize barrier function and to remove the antigens from the surface of the skin. Common anti-pruritic agents are 1% hydrocortisone, 0.01% fluocinolone, 2% diphenhydramine, 1% pramoxine, colloidal oatmeal and 0.015% triamcinolone acetonide. These variably come in shampoo, leave-on conditioners or sprays.

For dry scaling disorders, it is important to try to rehydrate the skin and improve barrier function. Most of these shampoos contain equal concentrations of sulfur and salicylic acid (2% of each). Colloidal sulfurs are the best as they are smaller and more efficacious than prepitated sulfurs.

For mild dry scaling disorders or to be used in conjunction with the sulfur:salicylic acid shampoos, you could consider moisturizing agents. Moisturizing agents help lubricate, rehydrate, soften the skin and restore an artificial superficial skin film. They can be diluted in water and massaged into the skin or applied undiluted as a spray. They should not be washed off. Non-lipid emollients have rehydrating and softening properties. They decrease odor and improve coat appearance with the greasy effect. The high molecular weight of their active ingredients and their hygroscopic nature make them effective surface-protecting therapeutic agents. Examples include lactic acid, glycerin, propylene glycol, urea and chitosamide.

For oily scaling disorders, benzoyl peroxides, selenium sulfide (previously mentioned) and tars have potential. Benzoyl peroxides have previously been discussed. Tars are derived from the destructive distillation of bituminous coal or wood. Birch tar, juniper tar and coal tar are crude products that from beginning to end are increasingly irritating. Coal tar solutions (5-20%) produce a milder, more readily managed effect. Despite processing, all tars are malodorous, potentially irritating, photosensitizing and carcinogenic. Of course, the tar products are contraindicated in patients with previous sensitivities to tar, patients with dry scaling dermatoses and in our feline friends!

Since there are numerous shampoos that will comply with the above characteristics, you should look at price, availability of your local representative and be sure that you have covered your basic needs. At the minimum, people should carry a moisturizing, hypoallergenic shampoo, a sulfur salicylic acid shampoo, a benzoyl peroxide shampoo and either a 3-4% chlorhexidine shampoo or a combination chlorhexidine based shampoo (with ketoconazole or miconazole).

Antibiotics for use in canine pyoderma