TCAs — Adverse Effects & Toxicity
A two-week supply of amitriptyline can be a lethal dose. TCAs have the narrowest margin between therapeutic and fatal among all antidepressants — knowing the toxicity pattern saves lives.
Core Concept
Tricyclic antidepressants (amitriptyline, nortriptyline, imipramine) block reuptake of norepinephrine and serotonin but also antagonize muscarinic, histaminic, and alpha-1 adrenergic receptors — producing a predictable side-effect triad. Anticholinergic effects dominate: dry mouth, constipation, urinary retention, blurred vision, tachycardia. Antihistaminic action causes sedation and weight gain. Alpha-1 blockade produces orthostatic hypotension, especially dangerous in older adults. The critical NCLEX concern is TCA overdose. Toxicity presents with the "three Cs": Convulsions, Coma, and Cardiotoxicity. The hallmark ECG finding is a widened QRS complex (>100 ms). Cardiac arrhythmias — particularly ventricular tachycardia — are the leading cause of death. First-line treatment for TCA overdose is sodium bicarbonate IV, which narrows the QRS and reverses cardiotoxic sodium channel blockade. Nursing priorities include continuous cardiac monitoring, seizure precautions, and limiting prescription quantities for clients with suicidal ideation. Baseline and follow-up ECGs are standard before and during therapy. Teach clients to rise slowly, avoid alcohol, and never abruptly discontinue.
Watch Out For
Don't confuse TCA overdose cardiotoxicity (widened QRS, ventricular arrhythmias treated with sodium bicarbonate) with MAOI hypertensive crisis (severe hypertension treated with phentolamine). Students mix up TCA anticholinergic effects (dry, hot, tachycardic) with cholinergic crisis (wet, bradycardic) — they are physiologic opposites. TCA sedation is from histamine blockade, not from the antidepressant mechanism itself.
Clinical Pearl
Three Cs of TCA overdose: Convulsions, Coma, Cardiotoxicity. The antidote is sodium bicarbonate — think "bicarb for a big QRS."
Test Your Knowledge
3 quick questions — see how well you understood TCAs — Adverse Effects & Toxicity