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. One mL of 3% hydrogen peroxide liberates 10 mL of oxygen at standard temperature and pressure. The effervescent action mechanically helps remove pus and cellular debris from wounds and is useful to clean and deodorize infected tissue. 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. However, the use of hydrogen peroxide in partially closed spaces, such as operative wounds, may result in oxygen embolization due to dissection of gas under pressure into tissues. 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.
Accelerated hydrogen peroxide 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. Accelerated hydrogen peroxide 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. A disadvantage is the potential to damage soft metals, such as brass, copper, and aluminum, and carbon-tipped instruments.
Peracetic acid and the combination of peracetic acid (0.23%) and hydrogen peroxide (7.35%) have been recognized as useful sterilants and antiseptics, 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. They can be used over wide temperature (0º–40ºC) and pH (3–7.5) ranges and are not affected by organic matter. They are effective against bacteria, yeasts, fungi, and viruses at concentrations of 0.001%–0.003% and are sporicidal at 0.25%–0.5%. Consequently, peracetic acid products have been accepted worldwide in the food industry, including meat and poultry processing plants and dairies, and are replacing traditional disinfectants for some medical devices. Solutions of 0.2% peracetic acid applied to compresses effectively reduce 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 peroxymonosulfate is a broad-spectrum disinfectant with increasing use in barns and kennels. A 1% solution in water is highly effective against bacteria, viruses, and fungi, maintaining good activity in the presence of organic matter.
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 among the oldest 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.
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 and poloxamer-iodine) are combinations of iodine with a solubilizing agent or carrier; they are more stable and water soluble than older formulations. 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 (although contact dermatitis can result from repeated exposure) 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 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. It is irritating to the skin and mucous membranes, including the respiratory tract, and can cause severe bronchospasms and acute lung injury. It is widely used to disinfect water supplies and inanimate objects (eg, utensils, bottles, pipelines) in dairies, creameries, and milk houses. Chlorine dioxide has recently replaced chlorine as a disinfectant for drinking water in some jurisdictions, because it forms fewer by-products.
Inorganic chlorides include sodium hypochlorite solutions (bleach). A 2%–5% NaOCl solution is a commonly used and effective disinfectant. 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.