Overdose of Tricyclic Antedepressants

Features of Tricyclic Antidepressants overdose.

 

Tricyclic antidepressants inhibit reuptake of noradrenaline at nerve terminals, potentiating the action of adrenaline, noradrenaline and other catecholamines.

The patient may initially be asymptomatic for 2–3 hours as absorption occurs.
Signs:

CNS features:

Agitation → seizures → coma.
Anticholinergic features of the drug will cause pupils to be enlarged through this.

Cardiovascular features

These are secondary to quinidine-like membrane stabilizing effects.

• ↑ in catecholamines at autonomic synapses.
• Anticholinergic effects.
• Tachycardia → PR prolongation → QT prolongation → QRS prolongation.
• Hypertension → CV collapse.
• Proceeds to any of:
• right bundle branch block (RBBB)
• second- or third-degree heart block
• VF/VT/asystole.

The tricyclics have a very high degree of protein binding and they bind avidly to myocardial tissue, causing the above effects. The degree of binding to myocardium and the clinical features vary with pH:

• Alkalosis leads to reduced binding to myocardium and reduction in CVS effects.
• IV bicarbonate will result in improvement in clinical features.

 

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