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Drowsiness, orthostatic hypotension
Large overdose
Miosis
Severe hypotension
Tachycardia
Convulsions
Obtundation or coma
Prolongation of QRS interval or QT interval or both and ventricular arrhythmias
An acute extrapyramidal dystonic reaction may occur with therapeutic or toxic doses
Spasmodic contractions of the face and neck muscles, extensor rigidity of the back muscles, carpopedal spasm, and motor restlessness
More common with haloperidol and other butyrophenones, less common with atypical drugs
Severe rigidity, hyperthermia, and metabolic acidosis (neuroleptic malignant syndrome) may occasionally occur and are life-threatening
Atypical antipsychotics have also been associated with weight gain and diabetes mellitus, including diabetic ketoacidosis
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Largely based on history of exposure
Most agents are not detected in routine rapid toxicology screens
Serum levels are not helpful
ECG monitoring for QRS, QT prolongation
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Activated charcoal for large or recent ingestions
Widened QRS interval
Hypotension often responds to intravenous saline boluses; cardiac arrhythmias associated with widened QRS intervals on the ECG may respond to intravenous sodium bicarbonate as is given for tricyclic antidepressant overdoses
Prolonged QT interval or torsades de pointes, or both
Treat hyperthermia, maintain cardiac monitoring
For extrapyramidal signs
Diphenhydramine, 0.5–1.0 mg/kg intravenously, or benztropine mesylate, 0.01–0.02 mg/kg intramuscularly
Continue with oral doses for 24–48 hours
Bromocriptine (2.5–7.5 mg daily orally) may be effective for mild or moderate neuroleptic malignant syndrome
Dantrolene (2–5 mg/kg intravenously) has also been used for muscle contractions but is not a true antidote