Peroxides

These compounds generally exert a short-acting germicidal effect on most organisms through release of nascent oxygen, which irreversibly alters microbial proteins. Most have little or no action on bacterial spores. Nascent oxygen is rendered inactive when it combines with organic matter.

Hydrogen peroxide solution (3%) liberates oxygen when in contact with catalase present on wound surfaces and mucous membranes. The effervescent action mechanically helps remove pus and cellular debris from wounds and is valuable for cleaning and deodorizing infected tissue. However, the antimicrobial action is of short duration and is limited to the superficial layer of the applied surface because there is no penetration of the tissue. Although its usefulness as an antiseptic is limited, hydrogen peroxide is finding increased application as a disinfectant in water treatment and food processing facilities and for sterilization of dental and surgical instruments.

Recently developed accelerated hydrogen peroxide (AHP) formulations are synergistic blends of 0.5–2% hydrogen peroxide with anionic and nonionic surfactants and stabilizers that possess broad-spectrum antimicrobial activity. They are effective against bacteria, spores, mycobacteria, viruses, and fungi, with short contact times. AHP formulations are nonirritating to eyes and skin and are biodegradable, decomposing to water and oxygen with no active chemical residues. They have become leading disinfectants in human hospitals and dental clinics in recent years. A disadvantage is the potential to damage soft metals, such as brass, copper, and aluminum, and carbon-tipped instruments.

Peracetic acid has been recognized only recently as a useful sterilant and antiseptic, combining the broad antimicrobial spectrum and lack of harmful decomposition products of hydrogen peroxide with greater lipid solubility and freedom from inactivation by tissue catalase and peroxidase. It has been accepted worldwide in the food industry, including meat and poultry processing plants and dairies. It is effective against bacteria, yeasts, fungi, and viruses at concentrations of 0.001–0.003% and is sporicidal at 0.25–0.5%. Solutions of 0.2% peracetic acid applied to compresses are effective at reducing microbial populations in severely contaminated wounds.

Sodium perborate, used in antiseptic solutions and in mouthwashes, acts by decomposing into sodium metaborate and hydrogen peroxide, which then gradually liberates oxygen.

Benzoyl peroxide slowly releases oxygen to act as an antiseptic. However, it can cause skin irritation. It also has keratolytic and antiseborrheic activity, which makes it useful in treating pyoderma in dogs.

Potassium permanganate has broad antimicrobial properties, but its intense purple color in solution, which stains tissues and clothing brown, is a disadvantage. It is an effective algicide (0.01%) and virucide (1%) for disinfection, but concentrations >1:10,000 tend to irritate tissues. Old solutions turn chocolate brown and lose their activity.

Halogens and Halogen-Containing Compounds

Iodine and chlorine are used as topical antimicrobial agents. They owe their activity to high affinity for protoplasm, where they are believed to oxidize proteins and interfere with vital metabolic reactions.

Iodine

Elemental iodine is a potent germicide with a wide spectrum of activity and low toxicity to tissues. A solution containing 50 ppm iodine kills bacteria in 1 min and spores in 15 min. It is poorly soluble in water but readily dissolves in ethanol, which enhances its antibacterial activity.

Iodine tincture contains 2% iodine and 2.4% sodium iodide (NaI) dissolved in 50% ethanol; it is used as a skin disinfectant. Strong iodine tincture contains 7% iodine and 5% potassium iodide (KI) dissolved in 95% ethanol; it is more potent but also more irritating than tincture of iodine. Iodine solution contains 2% iodine and 2.4% NaI dissolved in aqueous solution; it is used as a nonirritant antiseptic on wounds and abrasions. Strong iodine solution (Lugol's solution) contains 5% iodine and 10% KI in aqueous solution.

Iodophores (eg, povidone-iodine) are water-soluble combinations of iodine with detergents, wetting agents that are solubilizers, and other carriers. They slowly release iodine as an antimicrobial agent and are widely used as skin disinfectants, particularly before surgery. They do not sting or stain. Iodophores are nontoxic to tissues but may be corrosive to metals. They are effective against bacteria, viruses, and fungi but less so against spores. Iodophor solutions retain good antibacterial activity at pH <4, even in the presence of organic matter, and often change color when the activity is lost. Phosphoric acid is often mixed with iodophores to maintain an acidic medium. They have been used in teat dips to control mastitis, as dairy sanitizers, and as a general antiseptic or disinfectant for various dermal and mucosal infections.

Chlorine

Chlorine exerts a potent germicidal effect against most bacteria, viruses, protozoa, and fungi through formation of undissociated hypochlorous acid (HOCl) in water at acid to neutral pH. It is effective against most organisms at a concentration of 0.1 ppm, but much higher concentrations are required in the presence of organic matter. Alkaline pH ionizes chlorine and decreases its activity by reducing its penetrability. Chlorine has a strong acid smell and is an irritant to the skin and mucous membranes. It is widely used to disinfect water supplies and inanimate objects (eg, utensils, bottles, pipelines) in dairies, creameries, and milk houses.

Inorganic chlorides include sodium hypochlorite solutions (bleach). A 5% NaOCl solution decomposes on exposure to light. A 2–5% NaOCl solution can be used as a disinfectant, and a more diluted form (0.5%) can be used for irrigating suppurating wounds, but it dissolves blood clots and delays clotting. Calcium hypochlorite is used as a disinfectant.

Organic chlorides contain chlorine weakly bonded to nitrogen, which is slowly released for germicidal activity. They are generally less irritant, more stable, and more convenient to use than hypochlorite solutions.

Last full review/revision March 2012 by Mark L. Wickstrom, DVM, MS, PhD