The third serial of this topic- poisoning in MRCP, I am going to talk about tricyclic antidepressants. Examples of tricyclic antidepressants are amitriptyline, imipramine, doxepin etc.It is a common case scenario you would see during your internship/ housemanship. The reason is simple, doctors prescribe tricyclic antidepressants for patients with depression and these patients tend to use drugs for suicide.
As you might remember, tricyclic antidepressants help depressed patients through inhibition of reuptake of noradrenaline or serotonin in the brain, however, there are a few other effects of tricyclic antidepressants that explain its side effects,
1) it has central and peripheral anticholinergic effects2) it causes depression of cardiac contractility
3) it slows down intraventricular and artrioventricular conduction ( cardiac conduction)
4) it causes CNS toxicity such as agitation, confusion , coma and seizures
Symptoms of Toxicity
Remember that all these symptoms are due to cardiac toxicity and anticholinergic effects of tricyclic antidepressants.
Cardiac toxicity
Cardiac arrhythmias, supraventricular or ventricular arrhythmias leading to hypotension, pulmonary oedema, therefore patients may present palpitation and breathlessness
Anticholinergic toxicity ( autonomic toxicity)
Dry mouth, urinary retention, dilated pupils, constipation and hyperreflexia
CNS toxicity
Seizures ( may cause severe metabolic acidosis), coma, confusion
Treatment
Gastric lavage
Continuous cardiac monitoring is mandatory
IV Sodium Bicarbonate may be useful to maintain arterial PH if patients develop severe metabolic acidosis
DC shock may be needed, however, anti-arrhythmias are contraindicated
Fluid resuscitation if hypotension
Haemodialysis is not useful.
Tips for MRCP
1) Remember that if you see a patient with dilated pupils, confusion and cardiac arrhythmias , always consider tricyclic antidepressants.
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