Excerpt from Toxicity, Alcohols

Synonyms, Key Words, and Related Terms: alcohol ingestion, alcohol toxicity, alcohol poisoning, ethanol poisoning, ethanol toxicity, ethanol, methanol poisoning, methanol toxicity, methanol, isopropanol toxicity, isopropanol poisoning, isopropanol, ethyl alcohol toxicity, ethyl alcohol poisoning, ethyl alcohol, methyl alcohol toxicity, methyl alcohol poisoning, methyl alcohol, isopropyl alcohol toxicity, isopropyl alcohol poisoning, isopropyl alcohol, CNS depressant, alcohol metabolism, acute alcohol intoxication

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Background: The 3 most common alcohol poisonings result from ethanol, methanol, and isopropanol (isopropyl alcohol). The devastating and potentially life-threatening toxicity that results from ingestions of any of these alcohols makes recognition of alcohol poisoning an essential part of emergency medicine.

Recognition of the morbidity and mortality that may result from ingestion of small quantities of methanol is particularly important. Ethylene toxicity is covered in a separate article (see Toxicity, Ethylene Glycol).

Pathophysiology: The organs that are most severely affected vary depending on the type of alcohol ingested.

Ethanol

Ethanol (ethyl alcohol) is an aliphatic alcohol present in aftershaves, colognes, perfumes, mouthwashes, over-the-counter (OTC) medications, and a myriad of alcoholic beverages.

Ethanol is a direct CNS depressant, which causes decreased motor function and decreased consciousness level. At high concentrations, ethanol is an anesthetic and can cause autonomic dysfunction (eg, hypothermia, hypotension), coma, and death from respiratory depression and cardiovascular collapse.

Ethanol is easily absorbed from the stomach and small intestine. When the stomach is empty, peak levels are reached 30-90 minutes after acute ingestion. When food is present in the stomach absorption is delayed. Total absorption may take as long as 6 hours.

Metabolism of ethanol is carried out in the liver by several enzymes, including alcohol dehydrogenase, aldehyde dehydrogenase, microsomal ethanol-oxidizing system (MEOS) or CYP2E1, and peroxisomal catalase. Most (90-95%) enzymes are metabolized by alcohol and aldehyde dehydrogenases. MEOS accounts for about 5% but may increase to 25% in the chronic drinker. Normally, catalase makes a small contribution to ethanol metabolism; its role is more significant at high serum ethanol concentrations.

Nonhabituated patients metabolize ethanol at 13-25 mg/dL/h. In persons with alcoholism, this rate increases to 30-50 mg/dL/h. Metabolism rates vary greatly between individuals and cannot be predicted. Similarly, because of tolerance, blood alcohol concentrations (BACs) must be interpreted in conjunction with history and clinical presentation. Some individuals with chronic alcoholism may have an almost normal mental status and neurological examination, yet have BACs of 400 mg/dL. Conversely, nonhabituated drinkers may show marked effects of intoxication at very low BACs.

Methanol

Methanol (methyl alcohol) is found in cleaning materials, solvents, paints, varnishes, Sterno fuel, formaldehyde solutions, antifreeze, gasohol, "moonshine," windshield washer fluid (30-40% methanol), and duplicating fluids.

A CNS depressant, methanol is potentially toxic in amounts as small as a single mouthful. When metabolized by hepatic alcohol and aldehyde dehydrogenase, methanol forms formaldehyde and formic acid, both of which are toxic. The eyes, CNS, and GI tract are affected. Formic acid is the primary toxin that accounts for the majority of the anion gap, metabolic acidosis, and ocular toxicity. Lactic acid also contributes to the anion gap.

Formic acid inhibits cytochrome oxidase in the fundus of the eye. Disruption of the axoplasm is due to impaired mitochondrial function and decreased ATP production. Swelling of axons in the optic disc and edema result in visual impairment. Degradation of formic acid is folate dependent. Thus, if a folate-deficient person ingests ethanol, toxicity may be more severe due to the increased accumulation of formic acid.

Approximately 90-95% of methanol metabolism occurs in the liver, while 5-10% is excreted unchanged through the lungs and kidneys. Methanol is primarily metabolized by alcohol and aldehyde dehydrogenase. Formaldehyde has a short half-life, lasting only minutes. Formic acid is me .....