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Tricyclic Antidepressant (TCA) Toxicity is a potentially life-threatening condition that can occur following an overdose of TCAs, a class of medications commonly used for depression, chronic pain, and other psychiatric disorders. TCAs include drugs like amitriptyline, nortriptyline, imipramine, and doxepin. A QRS interval >100 ms is associated with an increased risk of seizures and arrhythmias. ECG monitoring is needed for at least 6 hrs. May need Plasma alkalinisation with IV Sodium Bicarbonate

About

• Actions and Toxicity due to the wide pharmacological effects of TCAs
• Toxicity due to the wide pharmacological effects of TCAs.
• Can cause death even in those who get to the hospital.
• Include amitriptyline, imipramine, dothiepin

Pharmacology

• Anticholinergic effects
• Direct alpha-adrenergic blockade
• Inhibition of norepinephrine and serotonin reuptake
• Blockade of fast Na channels in myocardial cells
• Block HERG K channels
• Histamine receptor blockers

Clinical

• Drowsiness - true - assess ABC and record and monitor GCS
• Dilated pupils, Convulsions are seen
• Urinary retention as anticholinergic properties of TCA's
• Hypotension, Arrhythmias - cardiac monitoring
• Ataxia, Nystagmus, hyperreflexia and increased tone
• Respiratory depression along with coma
• Hyperthermia, Increased reflexes generally

Investigations

• FBC, U&E, LFT, Lactate
• ABG: monitor to ensure pH rises if alkalinsation given target 7.45-7.55
• ECG: measure QRS width and QT. Prolonged PR, QRS and QT. Non-specific ST and T wave changes and AV block.
• CXR: if aspiration is suspected or breathless or sepsis
• CT head if unexplained coma
• Always wise to check paracetamol and aspirin levels

Management

• ABC O₂. IV fluids, CCU/ITU monitoring. Consider Plasma alkalinisation if SBP < 90 mmHg, QRS > 160 ms or pH < 7.1 or seizures and/or arrhythmias
• Consider Activated charcoal if > 10 tablets are ingested in the past 1-2 hours.
• Cardiac monitoring for the first 6-12 hours is advised. If QRS > 140 ms suggests (sodium channel blockade). Risk of fits/arrhythmias. Antiarrhythmics are avoided generally.
• Serum Alkalinisation will reduce free drug (Can use short boluses of Sodium Bicarbonate 50 mls of 8.4% IV or infusion of 1.26% sodium bicarbonate) where QRS prolonged or hypotension or arrhythmia and is useful therapy in overdose. Aim for alkalinisation of the serum to a pH level of 7.45-7.55 which increases protein binding, decreases the QRS interval, stabilises arrhythmias, and increase blood pressure in patients with TCA poisoning.
• Ventricular arrhythmias may be managed with overdrive pacing.
• Magnesium sulphate has been reported to treat ventricular tachycardia and ventricular fibrillation which failed to respond to other treatments. In those where this is not possible consider Sodium Bicarbonate and Lidocaine 100 mg IV. These drugs are highly protein-bound so haemodialysis is not indicated. The risk of further complications is uncommon after 24 hours.

References

• Tricyclic antidepressant overdose