Common antiseptics for veterinary use

Dr Hilary Lam BVSc, PgCert, MVS

Chemicals commonly used as antiseptics include: Alcohols (e.g. ethanol, isopropanol), Halogens (e.g. iodine idophores), Biguanides (e.g. chlorohexadine), Oxidizing agents (e.g. benzyl peroxide, hydrogen peroxide), Metals (e.g. merbromin, silver), Detergents (e.g. quaternary ammonium compounds). In this issue we will briefly focus on the most commonly encountered antiseptics avaliable in the market.

Alcohols

Examples of alcohols antiseptics include ethyl alcohol (70% ethanol), isopropyl alcohol (50% isopropanol). Isopropanol is slightly more potent than ethanol because of its greater depression of surface tension. Alcohol-based rinses have rapid acting antiseptic and wide germicidal effects. It has limited residual activity due to evaporation. Its efficacy will be reduced in present of organic matter and it is not effective against bacterial or fungal spores. It can be safely used on intact skin surface as "Rubbing Alcohol", however it is not indicated to be use on large or deep wound, eyes and mucosal surfaces.

Halogens

Iodine is a potent germicidal agent with a wide spectrum of acitivity and low toxicity to tissue. When iodine dissolves in ethanol, its antibacterial acitivity will be enhanced. Iodine alone has limited activity in presence of organic matter. Povodine iodine (PVP-I) is effective against bacteria, viruses, fungi and spore and its activity will not be affected in presence of organic matter. PVP-I as been found to kill 99% of methicilin-resistant Staphylococcus aureus after 10 seconds contact . It is important to note that its activity is lost when color change is observed. In general it does not sting, but may cause staining and may be corrosive to metals. Its use in animals with thyroid disease should be avoided.

Biguanides

Chlorohexadine 0.1% aqueous solution has potent activity against gram-positive bacteria. It is not effective against gram-negative bacteria, spores, and most viruses. Its function will be affected by high level of organic matter such as pus, blood or hard water. 4% emulsion of chlorhexadine gluconate is used as skin cleanser for veterinary patients with dermatological problem. Chlorohexadine activity can be enhanced by alcohols their mixtures (e.g. 0.5% chlorohexadine in 70% isopropanol), which is commonly found in hand rinse. It is commonly used as a wound cleanser, surgical scrubs due its antiseptic properties and low potential for systemic toxicity.

Oxidizing agents

Hydrogen peroxide 3% has effervescent action that liberates oxygen when in contact with catalase present on wound surface and mucous membrane. It can remove pus and cellular deris. However its use is limited by irritation and toxic to the underlying tissue, furthermore, its action is short acting and limited to the surperficial layer of the applied surface.

Benzoyl peroxide is commonly found in petshop products or over-the-counter in human pharmacy. Benzoyl peroxide slowly releases oxygen to act as antiseptic. It is ocassionally used to treat pyoderma in dogs, and it also has keratolytic and antiseborrheic activity. It may cause some skin irritation in some patients.

Metals

Merbromin is an organomercuric disodium salt compound. It stains tissue a brilliant red tinged color with a yellow green fluorescence. It is a weak antiseptic and will have limited acitvity in presence of organic matter and alkaline environment. Use of mercurial aneitseptics has decreased, partily because of their environmental persistence and contaminat potential. It should be avoided in large wound which may result in toxicity due to significant absorption.

Silver compounds can have caustic, antibacterial effect. 0.1% aqueous silver solution is bactericidal but some what irritating, whereas a 0.01% solution is bateriostatic. Colloidal silver compounds, which release silver ions slowly, are bacteriostatic and have a more sustained effect. They do not irritate tissue and have little astringent or caustic effect. They are generally used as mild antiseptics and in ophthalmic preparations.

Detergents

Quarternary ammonium compounds examples include benzalkonium chloride, benzathonium chloride, cetylpyridnium chloride, dodecyl dimethyl ammonium bromide, dioctyl dimethyl ammonium bromide ) with an ionizable halogen such as bromide, iodide, or chloride. Quarternary ammonium compounds are effective against most bacteria, enveloped viruses, some fungi, protozoa but not effective against non-enveloped viruses, mycobacteria and spores. The major site of action appears to be the cell membrane. The activity of older generation of the compounds will be reduced by hard water, porous or fibrous materials that absorb them. Soap, proteins, fatty acids, phosphates, blood and tissue debris will limit its use. Aqueous solution 1:1,000 to 1:5,000 have good antimicrobial activity and is commonly used as disinfectant for instruments and surfaces. Concentration > 1% will injury to mucous membranes. When applied to skin they may form a film under which micro-oganisms can survive, which limits the reliablity as antiseptics.