SAQ 465 – Toxicology – anticholinergic delirium after promethazine overdose

Toxicology – anticholinergic delirium after promethazine overdose.

a. Diagnosis

• Anticholinergic syndrome/toxidrome with delirium.

b. Other precipitants

• Other sedating antihistamines.
• Tricyclic antidepressants.
• Antipsychotics such as quetiapine, olanzapine, chlorpromazine or droperidol.
• Carbamazepine.
• Atropine, homatropine or benztropine.
• Anticholinergic plants such as Datura/Angel's trumpet.

c. Clinical signs

• Mydriasis.
• Tachycardia.
• Dry mouth and dry flushed skin.
• Hyperthermia.
• Absent bowel sounds or urinary retention.
• Tremor, mumbling speech, hallucinations or rarely seizures.

d. Treatment

• Use verbal reassurance, a calm low-stimulation environment and family support; temporary physical restraint only if required for safety.
• Check for urinary retention and insert a urinary catheter if needed.
• Give titrated IV benzodiazepine for gentle sedation, for example midazolam 2.5-5 mg IV increments or diazepam titrated to effect.
• If severe agitation persists, give physostigmine 0.5-1 mg IV slowly, titrated to effect, to a usual maximum of 4 mg with senior/toxicology input.
• Avoid anticholinergic sedatives such as olanzapine in this toxidrome.