Tricyclic Anti-depressant Overdose
4/11/10
PY Mindmaps
Life in the Fast Lane
- weak bases (pKa 8.5)
PROBLEMS
1. anticholinergic effects
2. inhibition of catecholamine reuptake (initial increase in sympathetic tone -> prolonged
decrease)
3. profound alpha-adrenergic blockade
4. myocardial toxicity
HISTORY
- having taken a large quantity of TCA (patients may be asymptomatic for 2-3 hours post
ingestion)
- will develop signs of major toxicity within 6 hours
- > 10mg/kg potentially life threatening
- > 30mg/kg will develop pH dependent toxicity + coma for more than 24 hours
EXAMINATION
- CVS – dry mucous membranes, tachycardia, hypertension -> hypotension -> cardiovascular
collapse (arrhythmia), postural hypotension, dehydration
- CNS – nystagmus, dizziness, agitation, decreases level of consciousness, unconscious/coma,
seizures, increase in tone, clonus, tremor, hypereflexia, pupillary dilation, blurred vision
- GI – N+V, abdominal pain, dry mouth, ileus
- METABOLIC – severe metabolic acidosis, fever
- GU – urinary retention
- SKIN – flushed
- anti-cholinergic: “blind as a bat, red as a beet, hot as a hare, dry as a bone, mad as a
hatter”
INVESTIGATIONS
ABG - metabolic acidosis
ECG:
-> sinus tachycardia
-> PR prolongation
-> RAD
-> R wave > 3mm in aVR
-> prolonged QT interval (>430ms)
-> QRS prolongation (>100ms)
-> VF/VT/asystole
-> 2nd or 3rd HB
Jeremy Fernando (2011)
-> RBBB
Bloods – renal impairment
MANAGEMENT
Resuscitation
- supportive care of airway, breathing and circulation
- a number of anti-arrhythmics are contra-indicated as they prolong depolarisation -> use
lignocaine, phenytoin, Mg2+, hypertonic saline.
- often need PAC
- volume resuscitation
- treat seizures with benziodiazepines, phenytoin, propofol and phenobarbital
Electrolyte and Acid-base Abnormalities
- IV NaHCO3 + hyperventilation to ensure pH is >7.5
How NaHCO3 works:
- TCA are weak bases
- increasing the serum pH with bicarbonate -> increases the proportion of non-ionised drug
which -> increase in drug distribution throughout rest of body and away from heart
- increased Na+ also overcomes the Na+ receptor blockade
- alkalinsation also accelerates the recovery of Na+ channels by neutralising the protonation
of the drug receptor complex
Specific Treatment
- see above
Underlying Cause
- prevent absorption: gastric lavage and charcoal if presents within 1 hour,
- enhanced elimination: haemodialysis not recommended in TCA OD c/o small amount of free
drug in plasma
Jeremy Fernando (2011)