Toxicology · Short notes

Drug Overdose Management: Short Notes & Cheat Sheet

Initial assessment, toxidromes, decontamination, enhanced elimination and the management of paracetamol, salicylate, TCA and other overdoses.

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Short notes

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Managing a suspected overdose

Resuscitation comes before identification; decontamination is useful only early and only for suitable poisons.

Approach

Start with ABCDE, and check blood glucose in every patient with reduced consciousness.
Find out what was taken, how much, when, with what else, and whether it was intentional.
Check paracetamol and salicylate levels in every intentional overdose, plus an ECG, blood gases and electrolytes.
Toxidromes: opioid (pinpoint pupils, slow breathing, coma), anticholinergic (dilated pupils, hot dry skin, delirium), cholinergic (secretions, miosis), sympathomimetic (dilated pupils, sweating, tachycardia, agitation) and serotonin syndrome (clonus, fever).

Decontamination and elimination

Activated charcoal (50 g in adults, 1 g/kg in children) within 1 hour, if the airway is safe.
Charcoal does not bind alcohols, iron, lithium, metals, acids, alkalis or hydrocarbons.
Multiple-dose charcoal enhances elimination of carbamazepine, dapsone, phenobarbital, quinine and theophylline.
Whole-bowel irrigation (polyethylene glycol) is for iron, lithium, sustained-release tablets and drug packets. Ipecac is no longer used.
Urinary alkalinisation increases elimination of salicylates and phenobarbital. Haemodialysis is used for salicylates, lithium, methanol, ethylene glycol, theophylline and metformin-associated lactic acidosis.

Specific overdoses

Paracetamol: potentially toxic above about 150 mg/kg. Plot a level taken at 4 hours or later on the treatment nomogram and give IV N-acetylcysteine; it is most effective within 8 hours. Staggered overdoses are treated regardless of the level.
Salicylate: tinnitus, hyperventilation, respiratory alkalosis then metabolic acidosis. Give IV sodium bicarbonate to alkalinise the urine (target urine pH 7.5–8.5); dialyse if severe.
Tricyclic antidepressants: anticholinergic features, seizures and a wide QRS (over 100 ms). Give sodium bicarbonate. Avoid flumazenil and physostigmine.
Opioids: naloxone 0.4 mg IV, repeated as needed (smaller titrated doses in dependent patients); an infusion for long-acting opioids such as methadone.
Digoxin: Fab fragments. β-blockers: glucagon and high-dose insulin. Calcium channel blockers: calcium and high-dose insulin. Sulfonylureas: glucose and octreotide.

Cheat sheet

High-yield facts in one place. Cover the right-hand column and test yourself.

Charcoal does NOT bind

Substance	Alternative
Iron	Whole-bowel irrigation, desferrioxamine
Lithium	Whole-bowel irrigation, dialysis
Alcohols (methanol, ethylene glycol)	Fomepizole, dialysis
Acids and alkalis	Endoscopy
Hydrocarbons	Supportive; protect lungs

Toxidromes

Toxidrome	Pupils · key features
Opioid	Pinpoint · slow breathing, coma
Anticholinergic	Dilated · hot, dry, delirious, retention
Cholinergic	Small · secretions, bradycardia
Sympathomimetic	Dilated · sweaty, tachycardic, agitated
Sedative-hypnotic	Normal · drowsy, normal vital signs
Serotonin syndrome	Dilated · clonus, fever, agitation

Memory aids

Charcoal fails with 'PHAILS': Pesticides (some), Hydrocarbons, Acids/alkalis, Iron, Lithium, Solvents (alcohols).

Exam traps

Every intentional overdose needs a paracetamol level, even if the patient denies taking it.
A paracetamol level taken before 4 hours cannot be plotted on the nomogram.
Sympathomimetic and anticholinergic toxidromes both cause dilated pupils; sweating distinguishes them (sympathomimetic = sweaty).
Flumazenil in a mixed overdose with tricyclics can cause seizures.

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