Metaldehyde is used widely in the United States as a snail and slug poison. In Europe and Japan, it is also used as a solid fuel (up to 100% metaldehyde) for small heaters. In Japan, tablets containing up to 90% metaldehyde are used for producing colored flames for entertaining. The pellets often are mistaken for cereal or candy. Common commercial products containing metaldehyde (2–4%) include Cory's Slug and Snail Death, Deadline for Slugs and Snails, and Bug Geta Snail and Slug Pellets.
Mechanism of toxicity
The mechanism of toxicity is not well understood. Metaldehyde, like paraldehyde, is a polymer of acetaldehyde, and depolymerization to form acetaldehyde may account for some of its toxic effects. Further metabolism to acetone bodies may contribute to metabolic acidosis.
Pharmacokinetics. Metaldehyde is readily absorbed, with onset of effects in 1–3 hours. Volume of distribution and protein binding are not known. The elimination half-life is approximately 27 hours.
Toxic dose. Ingestion of 100–150 mg/kg may cause myoclonus and convulsions, and ingestion of more than 400 mg/kg is potentially lethal. Death occurred in a child after ingestion of 3 g.
Clinical presentation. Symptoms usually begin within 1–3 hours after ingestion.
Small ingestions (5–10 mg/kg) cause salivation, facial flushing, vomiting, abdominal cramps, diarrhea, and fever.
Larger doses may produce irritability, ataxia, drowsiness, myoclonus, opisthotonus, convulsions, and coma. Rhabdomyolysis and hyperthermia may result from seizures or excessive muscle activity. Liver and kidney damage has been reported.
Metabolic acidosis and an elevated osmolar gap have been reported.
Diagnosis is based on a history of ingestion and clinical presentation. Ask about containers in the garage or planting shed; metaldehyde frequently is packaged in brightly colored cardboard boxes similar to cereal containers.
Specific levels. Serum levels are not generally available.
Other useful laboratory studies include electrolytes, glucose, BUN, creatinine, osmolar gap (may be elevated), and liver enzymes. If rhabdomyolysis is suspected, also perform a urine dipstick for occult blood (myoglobin is positive) and obtain a serum creatine kinase (CK).
Emergency and supportive measures
Maintain an open airway and assist ventilation if necessary (See Airway and Breathing).
Treat coma (See Coma and stupor) and seizures (See Seizures) if they occur.
Treat fluid loss from vomiting or diarrhea with IV crystalloid fluids (See Hypotension).
Monitor asymptomatic patients for at least 4–6 hours after ingestion.
Specific drugs and antidotes. There is no specific antidote.
Decontamination (See Decontamination). Administer activated charcoal orally if conditions are appropriate (see Table I–38). Do not induce vomiting because of the risk for abrupt onset of seizures. Gastric lavage is not necessary after small to moderate ingestions if activated charcoal can be given promptly.
Enhanced elimination. There is no apparent benefit from dialysis, hemoperfusion, or forced diuresis. Repeat-dose charcoal has not been studied.