Metaldehyde is a cyclic tetramer of acetaldehyde primarily used as a molluscicide for snails and slugs. It may be formulated in combination with other pesticides. Metaldehyde might rarely be found in solid fuel or fire starter pellets (up to 100% metaldehyde) or novelty products used to colorize flames (up to 90% metaldehyde) marketed outside of the United States. Because of its menthol-like odor and taste, poisonings have occurred when pellets were mistaken for edibles. The United States limits metaldehyde content in molluscicides to 4% and since 2001 has required the addition of the bittering agent denatonium benzoate, but other countries permit higher concentrations. Some products sold in the United States include Cory's Slug and Snail Death, Deadline for Slugs and Snails, and Bug Geta Snail and Slug Pellets.
The mechanism of toxicity is not well understood. Metaldehyde, like paraldehyde, is a polymer of acetaldehyde, but depolymerization into acetaldehyde does not account for most of its toxic effects. Although metaldehyde's CNS actions have not been fully elucidated, animal models have shown decreased GABA concentrations and increased MAO activity.
Pharmacokinetics. Metaldehyde is readily absorbed, and onset of symptoms usually begins within a few hours. However, case reports of large ingestions have suggested a prolonged absorption phase, and high levels did not begin to drop for 35 hours in one case. Volume of distribution and protein binding are not known. The elimination half-life is approximately 27 hours.
Small 5–10 mg/kg doses cause mild GI upset, but doses of 50 mg/kg or above are associated with CNS toxicity. 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.
Symptoms usually begin within 1–3 hours after ingestion, but might be delayed after lower doses. Symptoms continue to progress over several hours.
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. Seizure activity may be delayed as long as 10–14 hours based on current reports. Rhabdomyolysis and hyperthermia may result from seizures or excessive muscle activity. Liver and kidney damage has been reported.
Metabolic acidosis and an elevated osmol gap have been reported.
Is based on a history of ingestion and clinical presentation. The vomitus or breath may have an aldehyde odor because some of the metaldehyde can decompose into acetaldehyde in the stomach.
Specific levels. Serum levels are not generally available.
Other useful laboratory studies include electrolytes, glucose, BUN, creatinine, osmolality (osmol gap may be elevated), and liver enzymes. If rhabdomyolysis is suspected, also perform a urine dipstick for occult blood (myoglobin is positive) ...