Topical therapy is often used in mild cases of superficial pyoderma to reduce the cutaneous bacterial population but also to remove tissue debris, allowing direct contact of the active ingredient with the skin and promoting removal of the exudate. Some of these cases can be treated with shampoos alone, especially if they are used regularly. The frequency of applications may be then decreased depending on the animal’s response. Often other topical formulations like sprays or creams can also be used in addition or alternated to shampoos. In some cases systemic antibiotics may be administered to ensure a more prompt response, although the topical therapy may still play a supporting role. In the dog a common indication for long-term use of antiseptic shampoos or sprays is recurrent folliculitis, either idiopathic or secondary to endocrine or allergic skin diseases.
Chlorhexidine is a topical antiseptic commonly included in medicated shampoos that was first described in 1954. It is a divalent, cationic biguanide agent that exists as gluconate, acetate and hydrochloride salts. Chlorhexidine is most commonly used at various concentrations (0.5%–4%) of the water soluble gluconate form. Chlorhexidine acts by binding to the negatively charged bacterial cell wall and affecting the osmotic equilibrium of the cell. Briefly, the biguanide groups of the chlorhexidine molecules bind strongly to exposed anionic sites on the cell membrane and cell wall. The formation of bridges between adjacent phospholipid head groups displaces the divalent cations (Mg2+ and Ca2+) that naturally stabilize the cell membrane, and as a result the cell membrane becomes leaky to potassium ions and protons. At higher concentrations, binding of chlorhexidine causes the membrane to lose structural integrity, which results in bacterial cell death.
Chlorhexidine is mainly active against Gram-positive bacteria, but has also activity against Gram-negative bacteria, anaerobes, fungi and some enveloped viruses.
As well as a broad range of activity, a key potential advantage of chlorhexidine, especially when used as a skin disinfectant, is its ‘residual activity’. When compared with povidone iodine, chlorhexidine not only produces a greater reduction in the skin flora, it also has longer residual activity.
The safety and tolerability of chlorhexidine is good. It is less likely to cause dry skin than non-medicated soap and in one study it caused less dermatitis of the hands of nurses than soaps containing other antiseptic agents.
A recent published study comparing the efficacy of topical chlorhexidine (combined shampoo and spray formulations both at 4%) with systemic amoxicillin-clavulanic acid for the treatment of canine superficial pyoderma has shown that topical therapy with chlorhexidine digluconate products may be as effective as systemic therapy with amoxicillin-clavulanic acid. The combined topical therapy was reported to be effective even in dogs with a methicillin resistant Staphylococcus pseudintermedius (MRSP) infection when treated for 4 weeks.
Topical therapy is symptomatic and/or complimentary, and thus often used alongside or as an alternative to systemic treatments. The selection of an appropriate formulation, the judicious selection of the active ingredient and the appropriate frequency would bring great benefits to dermatological patients. These benefits will be achieved as long as the right amount of disinfectant is used and the recommended contact time is used. A good owner compliance is also essential for the perfect successful topical therapy. The advantages of the topical therapy and its effectiveness are tremendous when facing the increase in antimicrobial resistance in small animal practice and the need for alternative ways to manage infections caused by multi resistant bacteria.