Substance
Antihistamines: sedating (major classes)

[Other Names]
Alkylamines
Ethanolamines
Ethylenediamines
Phenothiazines
Piperazines

Pathology
Excessive central and peripheral anticholinergic effects.

Symptoms
Lethargy, agitation, confusion, miosis, tachycardia, hyperthermia, decreased GI motility, hypotension, respiratory depression, ataxia, stupor, seizures, dysrhythmias, coma, circulatory collapse, death.

Emergency Measures
Maintenance of airway, breathing, circulation, and fluids for hypotension; gastric decontamination by activated charcoal. If patient is sedated, intubate the airway. Give IV physostigmine for anticholinergic toxicity, benzodiazepines for seizures.

Comments
Most ingestions are complex to manage because many antihistamines are commercially available in combination with various analgesics and decongestants. With early intervention, most overdoses have excellent outcomes without consequences.