In this section : Poisoning
Paracetamol
SSRI Poisoning
Aspirin
Digoxin Poisoning
Tricyclic Antidepressants
Opiates
Benzodiazepines
Gut Decontamination
Deliberate Self Harm
Tricyclic Antidepressants
Last updated 3rd December 2020
Last updated on 19th May 2014 by Calum Murray
Toxicity
- Adults who have ingested a toxic dose or more (see below) or those who are symptomatic should be referred for medical assessment
- Toxic doses are those in excess of the following:
- Amitriptyline – 3 mg/kg
- Clomipramine – 4 mg/kg
- Desipramine – 3 mg/kg
- Dosulepin (Dothiepin) – 3 mg/kg
- Doxepin – 4 mg/kg
- Imipramine – 4 mg/kg
- Lofepramine – 15 mg/kg
- Maprotiline – 3 mg/kg
- Nortriptyline – 2.5 mg/kg
- Trimipramine – 5 mg/kg
Clinical Features
- OD on TCAs remains an important cause of poisoning deaths. Significant toxicity can occur with doses as low as 5-10mg/kg and would be to occur with 15mg/kg
- Common features of TCA poisoning include anticholinergic effects: warm dry skin, tachycardia, blurred vision, dilated pupils, dry mouth, urinary retention.
- Severe poisoning manifests as: drowsiness, coma, fits, arrhythmias, hypotension, metabolic acidosis, respiratory depression, serotonin syndrome
- ECG abnormalities include widening of the QRS interval, QT prolongation and ventricular dysrhythmias. Less commonly, SVT and bradyarrhythmias can also occur.
Serotonin Syndrome
- More likely to occur if patient has been exposed to two or more drugs that increase the effect of serotonin in serotonergic synapses, either as an acute overdose or if taken regularly, eg SSRIs, SNRIs, MAOIs, tricyclics, tramadol, triptans, linezolid and St John’s Wort; stimulant drugs e.g.ecstasy, amphetamines, cocaine.
- Features include CNS effects (including agitation or coma), autonomic instability (including hyperpyrexia), and neuromuscular excitability (including clonus and raised serum creatine kinase).
- Death of patients with serotonin syndrome is normally due to hyperpyrexia induced multi organ failure. It is therefore essential to rapidly lower temperatures greater than 39 degrees centigrade.
Management
- All patients should be on a cardiac monitor.
- Check ABGs to exclude and correct hypoxia, hypercapnia and acidosis. If hypercapnia present will likely require assisted ventilation
- Give activated charcoal PO or via N-G tube if patient presents within 1 hour of ingestion.
- Avoid antiarrhythmic drugs if at all possible, as all are potentially arrhythmogenic.
- Single brief convulsions do not require treatment. Control convulsions that are frequent or prolonged with diazepam 10-20 mg IV in adults; or lorazepam 4 mg IV; or midazolam 5-10 mg IV.
- Correct hypotension by adequate fluid resuscitation with a crystalloid.
- Give sodium bicarbonate 50 ml of 8.4% intravenously to all patients with QRS interval prolongation, arrhythmias, or hypotension and those with a metabolic acidosis. Repeated boluses can be given, aiming for a pH between 7.45 – 7.55.
- In the event of cardiac arrest, prolonged CPR/advanced life support should be instigated as per current resuscitation guidelines, but with early & aggressive use of hypertonic sodium bicarbonate.
- Do not give Flumazenil to reverse benzodiazepine toxicity if patient has also taken a tricyclic as will increase risk of seizure.
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