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Chlorhexidine and its Antimicrobial Action in the Skin
The skin is considered the largest organ of the body. It serves as a barrier to the external environment of an animal. From a book chapter by Ralf S. Mueller (2008) in the book Small Animal Clinical Pharmacology, he listed the numerous functions of the skin summarized in the table below.1
Table 1: Functions of the Skin1
|Protection against||Physical insults
|Secretion / excretion of||Sweat
|Vitamin D protection|
With this multitude of functions, skin is at risk to various diseases and conditions. In companion animal practice, skin diseases are quite common. Pruritus, reddening, and other visual changes such as scaling, greasiness and odor, flaking and presence of pus are just some of the most encountered signs in animals with skin disease.
Typically, the first approach when skin disease with abovementioned visual changes is encountered, topical treatment is initiated. Topical therapy is an important part of veterinary dermatology. It is often beneficial in improving the cosmetic appearance or odor of the animal, pending the final diagnosis. It can be beneficial as an adjunct to systemic therapy while for some diseases, may be the preferred method of treatment.2
There are various topical medications for the skin but for this technical bulletin, we focus on CHLORHEXIDINE.
Chlorhexidine is said to be one of the most widely used ‘biocide’ for topical products. Biocide is a general term describing a chemical agent, usually broad spectrum, which inactivates microorganisms (McDonnell and Russell, 1999).
Chlorhexidine has broad-spectrum efficacy, substantivity for the skin and low irritation. The effects of Chlorhexidine to different microorganisms are well researched. As in the article by McDonnell and Russell (1999), recent use of chlorhexidine gluconate has shown extremely rapid uptake by bacteria and yeasts, with maximum effect occurring within 20 seconds. Damage to the outer cell layers takes place but is insufficient to the induce lysis or cell death. The agent then crosses the cell wall or outer membrane, presumably by passive diffusion, and subsequently attacks the bacterial cytoplasmic or inner membrane or the yeast plasma membrane. In yeasts, chlorhexidine ‘partitions’ into the cell wall, plasma membrane, and cytoplasm of cells. This is followed by the leaking of intracellular constituents and is a consequence of cell death.3
In dogs and cats, Chlorhexidine is indicated for skin infections and dry to normal skin. It appears to have greater efficacy for bacterial infections, particularly Staphylococcus spp, than for yeast or dermatophyte infections. It is usually added in concentrations between 0.5% and 3%. Shampoos containing combinations of Chlorhexidine and Miconazole are available and have a superior action against yeast and fungal infections compared to shampoos containing Chlorhexidine only.1
Chlorhexidine is a cationic surfactant synthetic biguanide with broad-spectrum antibacterial and less pronounced antifungal activity works by disrupting microbial cell membranes and coagulates cytoplasmic proteins.1
With the information about Chlorhexidine as a topical agent and some background on topical therapy, here’s some of the guideline from a colleague expert on skin problems when prescribing topical therapy:2
- As much of the hair coat as possible should be removed when treating skin diseases. Good grooming practices facilitate topical therapy and can significantly help shorten the course of the disease.
- The cooperation of the owner (and animal) should be evaluated before any topical therapy is prescribed.
- 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.
- Tepid water is the temperature of choice for bathing animals.
- The old adage, “If it’s wet, dry it and if it’s dry, wet it,” has some truth to it; however, this advice should not be carried to extremes. Exudative lesions, eg, areas of pyotraumatic dermatitis, heal faster if they are kept clean and covered with an antibiotic ointment or gel (previous recommendations suggested aggressive astringent use). Dry, lichenified skin is often pruritic, and the judicious use of emollients may be beneficial.
- 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.2
1 Small Animal Clinical Pharmacology, 2008. Elsevier Health Sciences. Editors: Jill E. Maddison, Stephen W. Page, David B. Church
2 Moriello, Karen A. https://www.msdvetmanual.com/integumentary-system/integumentary-system-i...
3 McDonnell, Gerald and Russell, Denver. 1999. Clinical Microbiological Reviews. American Society of Microbiology.