Expansion
Anticholinergic, cardiac and neurological toxicity together
Expansion
Three groups of features
- Anticholinergic: dry mouth, dilated pupils, urinary retention, ileus, flushed dry skin, hyperthermia, confusion
- Cardiac: sinus tachycardia, broad QRS, prolonged QT, right axis deviation, a terminal R wave in aVR, hypotension, ventricular arrhythmia
- Neurological: agitation, seizures, coma
“Mad as a hatter, dry as a bone, and a wide QRS.”
The ECG is the key investigation, not the drug level:
- QRS over 100 ms predicts seizures
- QRS over 160 ms predicts ventricular arrhythmia
Treatment
- Sodium bicarbonate for a broad QRS, arrhythmia or acidosis, aiming for a pH of 7.45 to 7.55. It works by both alkalinisation and a sodium load, overcoming sodium channel blockade
- Benzodiazepines for seizures and agitation
- Activated charcoal if within 1 hour
- Fluids and, if needed, noradrenaline for hypotension
Avoid: class Ia and Ic antiarrhythmics and amiodarone, which worsen sodium channel blockade; flumazenil; and phenytoin for seizures.
Tricyclics remain among the commonest causes of death in overdose because toxicity develops quickly and the therapeutic index is narrow.