Tricyclic Antidepressants (TCA’s) are typically prescribed for managing neuropsychiatric disorders and chronic pain. TCA overdose can rapidly deteriorate and can be potentially lethal.
| Generic names | Brand name |
|---|---|
| Amitriptyline | Endep; Entrip |
| Clomipramine | Anafranil; placil |
| Dosulepin (dothiepin) | Dothep |
| Doxepin | Deptran; Sinequan |
| Imipramine | Tofranil |
| Nortriptaline | Allegron; Nortritabs |
Pharmacodynamics:
Therapeutically, TCA’s inhibit reuptake of norepinephrine and serotonin in the CNS. In toxicity they exhibit effects at multiple additional receptors including:
In cases of toxicity TCAs block numerous receptors:
- Cardiotoxicity (QRS prolongation / impaired cardiac contractility) due to sodium channel blockade
- Seizures due to sodium channel and GABA receptor blockade
- Vasodilatation / hypotension due to peripheral alpha-adrenergic blockade
- CNS depression due to histamine blockade
- Anticholinergic delirium / dry mouth / dry skin / urinary retention due to muscarinic blockade
- Drowsiness/confusion
- Tachycardia
- Slurred speech
- Hyperreflexia
- Ataxia
- Respiratory depression
Mild to moderate overdose
- Drowsiness/confusion
- Tachycardia
- Slurred speech
- Hyperreflexia
- Ataxia
- Respiratory depression
Severe overdose toxicity
- Coma
- Respiratory depression
- Prolonged QRS interval
- Hypotension
- Seizures
| Anticholinergic effect | Cardiotoxicity | Neurotoxicity |
|---|---|---|
| Agitation | Hypotension | Sedation/Coma |
| Dilated pupils | Prolonged PR and QRS interval | Seizures |
| Warm, dry, flushed skin | Prominent terminal R wave in aVR | |
| Hyperthermia | VT | |
| Tachycardia | ||
| Urinary retention |
- Large overdoses may result in rapid deterioration with coma, seizures and cardiac dysrhythmias
- Toxicity usually manifests within 2 hours, but any reported overdose requires at least 6 hours of observation
- >10mg/kg in adults and 5mg/kg in paediatrics is potentially life threatening
- All TCA overdoses require emergency department review
- Primary Survey
- Open, clear and maintain the airway
- Suction if required
- Insert oropharyngeal or nasopharyngeal airway (OPA/NPA) if required
- Lateral position if unresponsive (use left lateral position for pregnant women)
- Consider Oxygen with assisted ventilation if required (be aware of inadequate tidal volume)
- Full Vital Signs Survey, particularly GCS,
BGL and Pulse Oximetry
- Repeat vital signs every 10 minutes (5 minutes if patient appears time critical)
- Do not induce vomiting
- Complete Secondary Survey and manage injuries as required
- Make efforts to calculate the dose of the ingestion
- As per Primary Care guidelines
- Cardiac monitoring and 12-lead ECG
- Establish vascular access
- Consider obtaining prehospital blood sample
- Monitor patient persistently, recording full observations every 10 minutes (or 5 minutes if time critical)
- Manage cardiac dysrhythmia as required
- Manage seizures as required
- Consider fluid therapy as required
- Consider advanced airway management as required
- Transport Priority 1 if patient time critical, pre-notifying receiving facility
- in the event of a cardiac arrest, prolonged effective CPR in transit prehospital may still result in a good outcome
- As per Advanced Care guidelines
- Prehospital, good supportive care is the mainstay of treatment; particularly focusing on seizure control, optimising ventilation and maintaining circulation. Targeted therapies (eg IV sodium bicarbonate boluses and controlled hyperventilation) are instituted in hospital as indicated
- Efforts should be made to calculate the ingested dose
- Patients can deteriorate rapidly and TCA overdoses be fatal, consider peri-arrest if signs of instability. Cardiac arrest following a seizure is not uncommon in large overdoses
- Significant risk of arrhythmias - It is unlikely that defibrillation will be effective
- Urgent transport to hospital, where advanced treatments can be provided as indicated
| Settings | |
|---|---|
| Extended Care: | |
| Colour assist: | |
B. P, Tricyclic Antidepressant Toxicity [Online]. Available at: https://www.ncbi.nlm.nih.gov/books/NBK430931/ (Accessed: 1 May 2023).
R. Buttner, (2020). Pharm 101: Tricyclic Antidepressants [Online]. Available at: https://litfl.com/pharm-101-tricyclic-antidepressants/ (Accessed: 2 May 2023).
E. Burns, (2018). Tricyclic Overdose [Online]. Available at: https://litfl.com/tricyclic-overdose-sodium-channel-blocker-toxicity/ (Accessed: 2 May 2023).
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