Alcohols and aldehydes have been used as antiseptics and disinfectants for many years.5 Two of the most commonly used antiseptics and disinfectants are ethyl and isopropyl alcohol.
The antibacterial potencies of the primary alcohols (against test cultures of Staphylococcus aureus) increase with molecular weight until the 8-carbon atom octanol is reached. In general, one oxygen atom is capable of solubi-lizing seven or eight carbon atoms in water. As the primary alcohol chain length increases, van der Waals interactions increase, and the ability to penetrate microbial membranes increases. As water solubility decreases, the apparent antimicrobial potency diminishes with molecular weight. Branching of the alcohol chain decreases antibacterial potency; weaker van der Waals forces brought about by branching do not penetrate bacterial cell membranes as efficiently. The isomeric alcohols' potencies decrease in the order primary > secondary > tertiary. Despite this fact, 2-propanol (isopropyl alcohol) is used commercially instead of n-propyl alcohol, because it is less expensive. Isopropyl alcohol is slightly more active than ethyl alcohol against vegetative bacterial growth, but both alcohols are largely ineffective against spores. The activity of alcohols against microorganisms is the result of their ability to denature important proteins and carbohydrates.
Ethanol (ethyl alcohol, wine spirit) is a clear, colorless, volatile liquid with a burning taste and a characteristic pleasant odor. It is flammable, miscible with water in all proportions, and soluble in most organic solvents. Commercial ethanol contains approximately 95% ethanol by volume. This concentration forms an azeotrope with water that distills at 78.2°C. Alcohol has been known for centuries as a product of fermentation from grain and many other carbohydrates. Ethanol can also be prepared synthetically by the sulfuric-acid-catalyzed hydration of ethylene
The commerce in, and use of, alcohol in the United States is strictly controlled by the Treasury Department, which has provided the following definition for "alcohol": "The term alcohol means that substance known as ethyl alcohol, hydrated oxide of ethyl, or spirit of wine, from whatever source or whatever process produced, having a proof of 160 or more and not including the substances commonly known as whiskey, brandy, rum, or gin."
Denatured alcohol is ethanol that has been rendered unfit for use in intoxicating beverages by the addition of other substances. Completely denatured alcohol contains added wood alcohol (methanol) and benzene and is unsuitable for either internal or external use. Specially denatured alcohol is ethanol treated with one or more substances so that its use may be permitted for a specialized purpose. Examples are iodine in alcohol for tincture of iodine, methanol, and other substances in mouthwashes and aftershave lotions, and methanol in alcohol for preparing plant extracts.
The primary medicinal use of alcohol is external, as an antiseptic, preservative, mild counterirritant, or solvent. Rubbing alcohol is used as an astringent, rubefacient, and a mild local anesthetic. The anesthetic effect is results from the evaporative refrigerant action of alcohol when applied to the skin. Ethanol has even been injected near nerves and ganglia to alleviate pain. It has a low narcotic potency and has been used internally in diluted form as a mild sedative, a weak vasodilator, and a carminative.
Alcohol is metabolized in the human body by a series of oxidations:
Acetaldehyde causes nausea, vomiting, and vasodilatory flushing. This fact has been used in aversion therapy with the drug disulfiram, which blocks aldehyde dehydrogenase, allowing acetaldehyde to accumulate.
Alcohol is used in the practice of pharmacy for the preparation of spirits, tinctures, and fluidextracts. Spirits are preparations containing ethanol as the sole solvent, whereas tinctures are hydroalcoholic mixtures. Many fluidextracts contain alcohol as a cosolvent.
The accepted bactericidal concentration of 70% alcohol is not supported by a study that discovered that the kill rates of microorganisms suspended in alcohol concentrations between 60% and 95% were not significantly different.6 Concentrations below 60% are also effective, but longer contact times are necessary. Concentrations above 70% can be used safely for preoperative sterilization of the skin.7 Alcohols are flammable and must be stored in cool, well-ventilated areas.
Dehydrated ethanol, or absolute ethanol, contains not less than 99% w/w of C2H5OH. It is prepared commercially by azeotropic distillation of an ethanol-benzene mixture, with provisions made for efficient removal of water. Absolute ethanol has a very high affinity for water and must be stored in tightly sealed containers. This form of ethanol is used primarily as a chemical reagent or solvent but has been injected for the local relief of pain in carcinomas and neuralgias. Absolute alcohol cannot be ingested because there is always some benzene remaining from the azeotropic distillation that cannot be removed.
Isopropanol (2-propanol) is a colorless, volatile liquid with a characteristic odor and a slightly bitter taste. It is considered a suitable substitute for ethanol in most cases but must not be ingested. Isopropyl alcohol is prepared commercially by the sulfuric-acid-catalyzed hydration of propylene:
range of 50% to 95%. A 40% concentration is considered equal in antiseptic efficacy to a 60% ethanol in water solution. Azeotropic isopropyl alcohol, United States Pharmacopeia (USP), is used on gauze pads for sterilization of the skin prior to hypodermic injections. Isopropyl alcohol is also used in pharmaceuticals and toiletries as a solvent and preservative.
Ethylene oxide, C2H4O, is a colorless, flammable gas that liquefies at 12°C. It has been used to sterilize temperature-sensitive medical equipment and certain pharmaceuticals that cannot be heat sterilized in an autoclave. Ethylene oxide diffuses readily through porous materials and very effectively destroys all forms of microorganisms at ambient temo peratures.
The alcohol forms a constant-boiling mixture with water that contains 91% v/v of 2-propanol. Isopropyl alcohol is used primarily as a disinfectant for the skin and for surgical instruments. The alcohol is rapidly bactericidal in the concentration
Ethylene oxide forms explosive mixtures in air at concentrations ranging from 3% to 80% by volume. The explosion hazard is eliminated when the gas is mixed with sufficient concentrations of carbon dioxide. Carboxide is a commercial sterilant containing 10% ethylene oxide and 90% carbon dioxide by volume that can be handled and released in air without danger of explosion. Sterilization is accomplished in a sealed, autoclave-like chamber or in gasimpermeable bags.
The mechanism of the germicidal action of ethylene oxide probably involves the alkylation of functional groups in nucleic acids and proteins by nucleophilic opening of the oxide ring. Ethylene oxide is a nonselective alkylating agent, and for that reason is extremely toxic and potentially carcinogenic. Exposure to skin and mucous membranes should be avoided, and inhalation of the gas should be prevented by use of an appropriate respiratory mask during handling and sterilization procedures.
Formalin is a colorless aqueous solution that officially contains not less than 37% w/v of formaldehyde (HCHO), with methanol added to retard polymerization. Formalin is miscible with water and alcohol and has a characteristic pungent aroma. Formaldehyde readily undergoes oxidation and polymerization, leading to formic acid and paraformalde-
hyde, respectively, so the preparation should be stored in tightly closed, light-resistant containers. Formalin must be stored at temperatures above 15°C to prevent cloudiness, which develops at lower temperatures.
The germicidal action of formaldehyde is slow but powerful. The mechanism of action is believed to involve direct, nonspecific alkylation of nucleophilic functional groups (amino, hydroxyl, and sulfhydryl) in proteins and nucleic acids to form carbinol derivatives. The action of formaldehyde is not confined to microorganisms. The compound is irritating to mucous membranes and causes hardening of the skin. Oral ingestion of the solution leads to severe gastrointestinal distress. Contact dermatitis is common with formalin, and pure formaldehyde is suspected to be a carcinogen.
Glutaraldehyde (Cidex, a 5-carbon dialdehyde) is used as a dilute solution for sterilization of equipment and instruments that cannot be autoclaved. Commercial glutaralde-hyde is stabilized in alkaline solution. The preparation actually consists of two components, glutaraldehyde and buffer, which are mixed together immediately before use. The activated solution contains 2% glutaraldehyde buffered at pH 7.5 to 8.0. Stabilized glutaraldehyde solutions retain more than 80% of their original activity 30 days after preparation,9 whereas the nonstabilized alkaline solutions lose about 44% of their activity after 15 days. At higher pH (>8.5), glutaraldehyde rapidly polymerizes. Nonbuffered solutions of glutaraldehyde are acidic, possibly because of an acidic proton on the cyclic hemiacetal form. The acidic solutions are stable but lack sporicidal activity.
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