Ethanol Toxicosis: A Review

Ethanol Absorption

Ethanol is a central nervous system (CNS) depressant. It enhances the inhibitory effects of gamma-aminobutyric acid (GABA) at the GABA-A receptor and competitively inhibits the binding of glycine at the N-methyl-d-aspartate receptor (it disrupts excitatory glutaminergic neurotransmission).² Ethanol also stimulates release of other inhibitory neurotransmitters, such as dopamine and serotonin.

Ethanol is absorbed rapidly and completely from the stomach, small intestine, and colon. In humans, 80% to 90% is absorbed within 30 to 60 minutes.³ Ethanol can also be absorbed dermally, especially if the skin is not intact.² Peak plasma levels occur 30 minutes to 2 hours after ingestion but can be delayed after larger doses or in the presence of food.³ Although the time to reach peak plasma levels in these situations is increased, there is little difference in the amount absorbed.⁴ Most ingested ethanol (95%) is metabolized in the liver by alcohol dehydrogenase to acetaldehyde and then to acetic acid.³ About 5% to 10% is excreted unchanged in the breath, urine, sweat, and feces.^3,5,6

The elimination half-life is not meaningful because it is affected by saturation of the metabolizing enzymes.⁵ At lower concentrations, the elimination rate may be nonlinear (first-order reaction), but it becomes linear (zero-order reaction) at high concentrations when all the available alcohol dehydrogenase is occupied.⁵ In the average human adult, the blood level of ethanol decreases by 15 to 20 mg/dL per hour.⁶ In animals, the onset of action is typically within 1 hour of exposure; most animals recover within 12 to 24 hours.^7–9

The amount of ethanol needed to cause intoxication varies depending on its concentration in the substance ingested (Table 1). The published oral lethal dose in dogs is 5.5 to 7.9 g/kg of 100% ethanol.¹¹ One milliliter of ethanol is equal to 0.789 g. Kammerer et al reported a case of lethal ethanol toxicosis in a dog caused by the massive ingestion of rotten apples.¹²

Table 1 Ethanol Concentrations in Alcoholic Beverages and Other Household Products ^5,10

[ultimatetables 5 /]

Clinical Signs

The most common clinical signs of ethanol toxicosis are ataxia, lethargy, vomiting, and recumbency. In more severe cases, hypothermia, disorientation, vocalization, hypotension, tremors, tachycardia, acidosis, diarrhea, respiratory depression, coma, seizures, and death may occur.⁴

Alcohol is directly irritating to the stomach and causes vomiting. High ethanol blood levels also stimulate emesis. The concern with vomiting during intoxication is that at high blood ethanol concentrations, the muscles that control the epiglottis become slow to react or even paralyzed. This increases the risk for aspiration.¹³ Ethanol intoxication reduces peripheral oxygen delivery and metabolism and causes mitochondrial oxidative dysfunction, potentially resulting in shock or hypoxia in an acutely intoxicated patient.¹⁴

Hypothermia may result from multiple mechanisms. Peripheral vasodilation, CNS depression, ethanol interference with the thermoregulator mechanism, and/or impaired behavioral responses to a cold environment all lead to a lowered body temperature.³

Management

• Induce emesis only in asymptomatic animals. Activated charcoal is not indicated because it binds poorly to ethanol.¹⁵ In addition, because ethanol toxicosis is characterized by vomiting, the risk for charcoal aspiration is high.
• In cases of dermal exposure, bathe the animal to reduce both dermal absorption and ingestion resulting from grooming behaviors.
• Monitor heart rate and rhythm, blood pressure, and body temperature. Monitor for acidosis and calculate anion gap if possible. The normal anion gap for dogs and cats is 10 to 15 mEq/L. Values greater than 25 mEq/L are considered acidotic.¹⁶ Although there are no data on how often acidosis occurs in pets, about 45% of intoxicated humans become acidotic.¹⁷
• Monitor for hypoglycemia. If dietary and hepatic (glycogenolysis) sources of glucose are exhausted, hypoglycemia may result. During the oxidation of ethanol, the ratio between oxidized and reduced forms of nicotinamide adenine dinucleotide increases, which increases the conversion of pyruvate to lactate. This leads to a lack of the key intermediate in gluconeogenesis, pyruvate, and hypoglycemia ensues.¹⁸ Hypoglycemia, which can result in seizures and coma, is a serious complication of acute alcoholic intoxication.¹⁰ Dextrose may need to be added to IV fluids.
• IV fluids do not accelerate ethanol clearance in intoxicated patients but should be started for supportive purposes.¹⁹ Use isotonic solutions. Sodium bicarbonate (0.5 × kg body weight × base deficit = deficit in mEq) can be added to combat metabolic acidosis. Give half the sodium bicarbonate dose over 3 to 4 hours.²⁰
• Treat any arrhythmias symptomatically (atropine for bradycardia, lidocaine for ventricular premature contractions). Control seizures not related to hypoglycemia with diazepam. If the animal is comatose, pass an endotracheal tube and position the patient to prevent aspiration. In cases of severe intoxication, monitor oxygen saturation and be prepared to mechanically support the animal’s breathing. Yohimbine (0.11 mg/kg IV), atipamezole (100 mcg/kg IV), or naloxone (0.1 mg/kg IV) can be tried to reverse severe CNS depression or coma.²⁰ This reversal effect does not appear to be predictable or consistent in animals.²¹

Animals that are mildly affected may be monitored at home. Patients with significant CNS depression, those requiring airway protection or ventilatory support, and those with seizures, acid-base disturbances, or hypoglycemia should be admitted for monitoring and supportive care. In severe cases, hemodialysis may be considered. Keno and Langston reported using hemodialysis in a dog with rapid clinical recovery.²² Hemodialysis can eliminate ethanol approximately 3 to 4 times more rapidly than liver metabolism alone.

Although ethanol levels may be determined from blood, serum, plasma, and urine, they are seldom measured in pets.²³ In most cases, such measurements need to be performed at a human hospital. In humans, blood ethanol concentrations between 150 and 300 mg/dL (32.6 to 65.2 mmol/L) generally cause obvious signs and symptoms. Death is usually associated with blood ethanol levels >400 mg/dL (86.8 mmol/L).³ In the case report by Kammerer et al, the dog that ingested rotten apples exhibited vomiting, ataxia, tremors, and dehydration and died 48 hours later with an alcoholemia of 300 mg/dL.¹² If the blood ethanol level cannot be measured, serum or plasma osmolality may be used to estimate it, using the following formula²⁴:

Blood ethanol level [g/L] = Osmolal gap/27

Differential Diagnosis

Most ethanol intoxications are unmistakable because of the odor of alcohol on the pet’s breath. However, other toxic differentials for intoxicated patients include salicylates, marijuana, toluene, ethylene glycol, methanol, isopropanol, benzodiazepines, barbiturates, opiates, and gamma-hydroxybutyric acid.^7–9 Nontoxic differentials include lactic acidosis, uremia, diabetic ketoacidosis, cardiovascular accident, hypoglycemia, and hypoxia.^7–9

Prognosis

In most cases of ethanol ingestion, the prognosis is good. Cases complicated by aspiration of gastric contents, presence of other ingested material, or preexisting disease have a more guarded prognosis. Intoxicated animals are also predisposed to traumatic injuries.