TCA POISONING
TRICYCLIC ANTIDEPRESSANT POISONING (TCA POISONING)
Features of TCA overdose:
1. Mainly cardiotoxicity:
- Mainly cardiac (ventricular) arrhythmias – Results in mortality.
- Due to inhibition of cardiac fast Na+ channels –> Leading to, slowing of phase 0 depolarization in His-Purkinje tissue & myocardium.
- Other cardiotoxic features:
- Conduction defects
- Hypotension
- ECG changes like QRS & QT prolongation.
2. Anticholinergic signs:
- Hyperthermia
- Flushing
- Dilated pupils
- Mydriasis (Pinpoint pupil)
- Intestinal ileus
- Urinary retention
- Sinus tachycardia
3. Metabolic acidosis (pH3< 24 mmol/L).
4. CNS involvement also common.
- Early signs:
- Confusion, delirium & hallucinations, typically occur before onset of seizures or coma
- Physical examination:
- Reveals clonus, choreoathetosis, hyperactive reflexes, myoclonic jerk & positive Babinski sign.
Treatment:
- Treatment of TCA overdose must be aggressive from outset.
- Initial management:
- Establishing airway & breathing.
- Continuous electrocardiographic monitoring.
- Gastric lavage.
- Gastric decontamination considered for up to 12 hrs, after ingestion.
- Due to anticholinergic properties, delaying gastric emptying.
- Administration of activated charcoal.
- Intravenous fluids – Preferred for hypotensive patients.
1. First-line drugs:
- Intravenous sodium bicarbonate – Single most effective intervention.
- Particularly useful for cardiovascular toxicity.
- Additionally corrects metabolic acidosis.
2. Lignocaine – DOC for TCA-induced ventricular dysrhythmias.
3. Diazepam – DOC for management of acute-onset seizures.
4. Second-line drugs – Phenytoin or Phenobarbital.
5. Antidote for TCA poisoning:
- Physostigmine
- Short-acting cholinesterase inhibitor.
- Antidote because increases cholinergic tone & ability to reverse anticholinergic effects.
- Disadvantage:
- May causes severe bradycardia, seizures & asystole, by overcompensating for cholinergic tone, suppressing supraventricular & ventricular pacemakers.
- Hence, used only in comatose/convulsion/arrhythmic patients, resistant to standard therapy.
Exam Important
TRICYCLIC ANTIDEPRESSANT POISONING (TCA POISONING)
- TCA overdose mainly causes cardiotoxicity, particularly cardiac (ventricular) arrhythmias.
- Arrhythmia in TCA poisoning is due to inhibition of cardiac fast Na+ channels.
- TCA poisoning mainly features anticholinergic signs like hyperthermia, flushing, dilated pupils, mydriasis (pinpoint pupil).
- During TCA poisoning, metabolic acidosis with pH3< 24 mmol/L.
- Intravenous sodium bicarbonate is the single most effective intervention particularly cardiovascular toxicity, in TCA poisoning.
- Lignocaine is DOC for TCA-induced ventricular dysrhythmias.
- Diazepam is DOC for management of acute-onset seizures, in TCA poisoning.
- Antidote for TCA poisoning used only in comatose/convulsion/arrhythmic patients, resistant to standard therapy is Physostigmine.
Don’t Forget to Solve all the previous Year Question asked on TCA POISONING
