Drug Toxicities (NEM, Serotonin, Lithium, TCA etc.)

Question 1

What is a typical presentation of Tricyclic antidepressant overdose?

Answer 1

Most prominant feature of toxicity due to anticholinergic effects (almost similar to atropine poisonin)

• Cardiac: Sinus tachycardia, with prolonged QRS/ QT/ PR interval –> arrhythmias
• Hyperpyrexia (bc no sweating)
• CNS: coma, seizures,
• Other anticolinergic effects: dry mouth, dilated pupils

– Sinus tachycardia (heart rate: ∼143/min)
– Left-axis deviation (R > S in lead I; S > R in aVF)
– Widened QRS complexes (∼160 ms in lead II)
– QT prolongation (QTc ∼556 ms)
– Prominent R wave in aVR

In a patient with a drug overdose, wide complex sinus tachycardia with QT prolongation and a prominent R wave in aVR suggest sodium channel blocker toxicity (e.g., TCA).

Question 2

What is the management of TCA overdose?

Answer 2

1. Activated charcoal if within 2h of ingestion
2. Sodium bicarbonate (for caradiac stabelisation)
3. Benzodiazepines for termination of seizures

Question 3

At what serum level of lithium would you expect to see signs of lithium toxicity?

Answer 3

levels > 1.5 mEq/L.

(no dose - severity relatitonship)

Question 4

What are the clinical signs of lithium toxicity?

Answer 4

1. Gastrointestinal
* Nausea, vomiting, and diarrhea
* Further fluid loss may exacerbate lithium toxicity

**2. Neuromuscular **
* Coarse tremors, seizures, fasciculations, myoclonic jerks,
* Altered mental status, confusion
* Somnolence, coma
* Delirium, encephalopathy, psychomotor impairment
* Ataxia, slurred speech, nystagmus
* Hyperreflexia

3. Acute renal failure

Question 5

What are some causes of lithium totxicity?

Answer 5

1. Dose increase
2. AKI/ reduced renal excretion
3. Low circulating volume
4. Other medications (e.g. thiazide diuretics, NSAIDS, ACE)