Topical Therapy for Infectious Diseases

Chapter 102

Topical Therapy for Infectious Diseases

In recent years, there has been a disturbing trend toward less use of topical therapy in patients with infectious skin diseases in favor of sole use of veterinary and human systemic antibiotics. Combined use of systemic antibiotics and topical antimicrobial therapy is preferred because it produces more rapid resolution of infection, causes less microbial resistance from overuse of systemic antibiotics, and yields possible cost savings. Because staphylococcal resistance has emerged as a significant problem, treatment programs to slow this process (such as judicious use of systemic and topical antibiotics, and more frequent use of antiseptics in shampoo, spray, rinse, and wipe formulations) are critical parts of the treatment plan.

Currently a very large number of topical antimicrobial ingredients in many formulations are available for veterinary use. Most are not licensed by the Food and Drug Administration and have not undergone the same rigorous approval process as drugs. Therefore, there is a great deal of product variability, and more companies are encouraged to provide adequate efficacy, safety, and manufacturing quality data for claims associated with their products.

This chapter reviews current recommendations for the topical management of bacterial and yeast skin infections.

Basic Guidelines for Topical Antimicrobials

• Demonstration and written instructions should be provided to clients on the proper use of prescribed topical products: the reason to use them, the way to use them, the desired response, the duration of treatment, and the need for a recheck to follow progress.

• A gentle, general cleansing shampoo should be used before an antimicrobial shampoo to clean the skin and hair coat and minimize the amount of the more expensive medicated product.

• The hair coat should be kept short for easier and more successful management of recurrent infections.

• The client should be instructed to ensure at least 10 minutes of contact time with gentle lathering for antimicrobial shampoos.

• Tepid or cool water should be used and the animal should be rinsed very well, especially when skin is inflamed and pruritic.

• The animal should be bathed at least twice weekly to treat a cutaneous infection and then as needed for maintenance.

• Antimicrobial sprays, rinses, or wipes should be used between shampoos for continual and residual activity.

• Cytologic examination is extremely important before, during, and after treatment to gauge response.

Bacterial Pyoderma

Bacterial pyoderma caused by staphylococcal infections is the most common and important indication for combined therapy with systemic antibiotics and topical therapy. Vigilant use of topical antimicrobial formulations can successfully treat and control recurrent infections, while minimizing use of the systemic drugs. Bacterial skin infections are secondary to primary dermatoses such as those caused by allergies, parasites, endocrinopathies, autoimmune skin diseases, and immunosuppressive therapy; control of these diseases lessens the likelihood of recurrent infections.

The most common organism isolated from pyoderma lesions in dogs is Staphylococcus pseudintermedius (see Chapter 100). Several topical antiseptics and antibiotics are used to treat staphylococcal infections, including benzoyl peroxide, chlorhexidine, miconazole, ethyl lactate, and mupirocin, either alone or in combination. New products and technologies are needed to address emerging bacterial resistance in a safe and effective manner.

Benzoyl Peroxide

Benzoyl peroxide is metabolized in the skin to benzoic acid, which alters pH and acts as an oxidizing agent to damage bacterial cell membranes. It is clinically effective in staphylococcal pyoderma, has demonstrated superior prophylactic activity compared with complexed iodine and triclosan, and is used in shampoos and a gel (Table 102-1). Benzoyl peroxide has been formulated with sulfur and salicylic acid for enhanced keratolytic, degreasing, and antibacterial activity.

Because of its follicular flushing, comedolytic, keratolytic, and degreasing activity, benzoyl peroxide has most commonly been used in greasy dogs with pyoderma, with deep pyoderma, and with pyoderma associated with demodicosis. Repeated use of benzoyl peroxide shampoos on dogs with atopic skin disease may cause further disruption of epidermal barrier function and increased percutaneous penetration of potential allergens. Moisturizing agents and fatty acids have been added to some benzoyl peroxide shampoos to offset the epidermal lipid loss and excessive drying that might occur with frequent use. However, if repeated use is necessary, chlorhexidine, chlorhexidine and miconazole, chlorhexidine and phytosphingosine, or ethyl lactate–containing shampoos are preferred.


Chlorhexidine is a cationic biguanide antiseptic with activity against most of the common bacteria causing cutaneous infections. It is bactericidal by disrupting and increasing permeability of cell membranes of susceptible organisms. Chlorhexidine may have up to 48 hours of residual activity by adherence to the skin surface and hair coat because of its positive charge. It is generally nonirritating and rarely sensitizing, but may cause problems at high concentrations on mucous membranes and if ingested by puppies, kittens, and cats. Stability, bioavailability, and adherence characteristics of chlorhexidine can be significantly affected by the formulation into which it is incorporated. Chemical formulation of chlorhexidine is a challenge, and some marketed products may not meet label claims for potency and clinical efficacy. Unfortunately, comparative clinical efficacy studies and residual activity studies are lacking for most of the current veterinary formulations.

Dermatologists typically use 3% or 4% chlorhexidine shampoos (see Table 102-1). A recent clinical study documented better efficacy of a 3% chlorhexidine gluconate shampoo than of a 2.5% benzoyl peroxide shampoo used as sole therapy for canine superficial pyoderma (Loeffler et al, 2011). A Japanese study (Murayama et al, 2010) revealed comparable clinical activity for a 2% chlorhexidine acetate surgical scrub and a 4% chlorhexidine gluconate shampoo in 10 dogs with superficial pyoderma when treated twice per week. Additionally, in a population of seven dogs with methicillin-resistant staphylococcal (MRS) pyoderma treated with the 2% scrub every 2 days for 2 weeks, five dogs responded completely and one partially. Clinical efficacy may be more contingent on frequency of treatment than concentration of the active ingredient. For more residual activity, a chlorhexidine leave-on conditioner/rinse, spray, or wipe should be used between shampoos (see Table 102-1).

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Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on Topical Therapy for Infectious Diseases
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