Overdose of common drugs flashcards
27 high-yield MRCP Part 1 cards from the Intellect Medicos Clinical Pharmacology & Toxicology course. Try to answer each question before you open it — then study them properly with spaced repetition, which brings each card back just before you would forget it.
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Within what time after ingestion is a single dose of activated charcoal generally useful?
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Within 1 hour (for a substance that binds charcoal, in a patient with a safe airway).
Why? After an hour most of the drug has been absorbed, so benefit falls sharply.
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Name three substances that are NOT adsorbed by activated charcoal.
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Any three: iron, lithium, alcohols (ethanol, methanol, ethylene glycol), acids/alkalis (corrosives), other metal salts, petroleum distillates, cyanide, malathion.
Why? These are small ionised molecules, metals or corrosives that charcoal does not bind well.
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Name three drugs for which multiple-dose activated charcoal is used.
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Any three: theophylline, carbamazepine, quinine, dapsone, phenobarbital (barbiturates).
Why? Repeated charcoal interrupts enterohepatic/enteroenteric recirculation and adsorbs drug from slowly absorbing tablet masses.
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Name three poisons that can be removed by haemodialysis.
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Any three: barbiturates, lithium, toxic alcohols (methanol, ethylene glycol), salicylates, theophylline.
Why? Dialysable drugs have a small volume of distribution, low protein binding and low molecular weight.
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What is the toxic metabolite of paracetamol, and what normally detoxifies it?
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NAPQI (made by CYP2E1), normally detoxified by conjugation with glutathione.
Why? In overdose glutathione is used up, so NAPQI binds liver proteins and causes centrilobular (zone 3) necrosis.
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After a single acute paracetamol overdose of known time, when should the plasma level be taken?
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At 4 hours after ingestion (or as soon as possible after that).
Why? Levels before 4 hours are unreliable because absorption is incomplete.
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In UK practice, what 4-hour paracetamol level is the treatment line for acetylcysteine?
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100 mg/L (a single treatment line for all patients).
Why? Since 2012 the MHRA uses one line from 100 mg/L at 4 hours; patients on or above it get acetylcysteine.
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Name two situations in paracetamol overdose where acetylcysteine is started without waiting for a level.
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Any two: staggered overdose, unknown time of ingestion (treat as staggered), or presentation 8–24 hours after more than 150 mg/kg (or an unknown amount); also if a level will not be available until 8 hours or more after ingestion.
Why? A single level cannot be interpreted on the nomogram in these cases, and delay beyond 8 hours reduces the benefit of acetylcysteine.
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What is the most common adverse reaction to IV acetylcysteine, and how is it managed?
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An anaphylactoid (non-IgE) reaction, e.g. flushing, rash, wheeze. Pause the infusion, give an antihistamine, then restart.
Why? It is related to the infusion rate and peak acetylcysteine level, not true allergy, so it is not a reason to withhold the antidote. Reactions are less common with the 12-hour SNAP regimen.
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In paracetamol-induced liver failure, King's College criteria for transplant referral include arterial pH < ______ after resuscitation, OR all three of INR > 6.5, creatinine > 300 µmol/L and grade III–IV encephalopathy.
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7.3
Why? These features predict a poor outcome without liver transplantation.
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In paracetamol-induced liver failure, King's College criteria for transplant referral include arterial pH < 7.3 after resuscitation, OR all three of INR > ______, creatinine > 300 µmol/L and grade III–IV encephalopathy.
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6.5
Why? These features predict a poor outcome without liver transplantation.
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A 25-year-old woman is sweaty, confused and complains of ringing in her ears after an overdose. Blood gas: pH 7.38, low PaCO2, low bicarbonate, raised anion gap. What overdose and acid–base picture is this?
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Salicylate overdose: mixed respiratory alkalosis and high anion gap metabolic acidosis.
Why? Salicylates stimulate the respiratory centre early (alkalosis), then uncouple oxidative phosphorylation, causing a metabolic acidosis.
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Which treatment increases salicylate elimination in moderate toxicity?
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Urinary alkalinisation with IV sodium bicarbonate.
Why? Alkaline urine keeps salicylate ionised in the tubule so it cannot be reabsorbed (ion trapping). Watch potassium, which must be corrected.
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Name two indications for haemodialysis in salicylate poisoning.
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Any two: salicylate level above 700 mg/L, severe or refractory metabolic acidosis, seizures/CNS features, AKI, pulmonary oedema.
Why? Haemodialysis removes salicylate and corrects the acidosis quickly.
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In tricyclic overdose, which ECG finding is the key indication for IV sodium bicarbonate?
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QRS widening above 100 ms (also give it for arrhythmias, hypotension or acidosis, e.g. pH below 7.1).
Why? Tricyclics block cardiac sodium channels; sodium loading and alkalinisation reduce this block.
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Which electrolyte disturbance is typical of theophylline toxicity?
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Hypokalaemia (with hyperglycaemia and metabolic acidosis).
Why? Theophylline drives potassium into cells via beta-adrenergic stimulation. Severe toxicity causes seizures and arrhythmias.
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What is the specific antidote for beta-blocker overdose with bradycardia and hypotension not responding to atropine?
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IV glucagon.
Why? Glucagon raises cAMP in cardiac cells through its own receptor, bypassing the blocked beta-receptor.
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Which blood glucose finding helps distinguish calcium-channel blocker overdose from beta-blocker overdose?
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Hyperglycaemia in calcium-channel blocker overdose (beta-blocker overdose tends to cause hypoglycaemia).
Why? Blocking L-type calcium channels in beta cells reduces insulin release.
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Name the two specific therapies for severe calcium-channel blocker overdose.
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IV calcium and high-dose insulin (with glucose).
Why? Calcium partly overcomes the channel block; high-dose insulin improves myocardial use of glucose and contractility.
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What is the specific treatment for life-threatening digoxin toxicity?
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Digoxin-specific antibody (Fab) fragments.
Why? The fragments bind free digoxin and are excreted by the kidneys. Indications include life-threatening arrhythmias and severe hyperkalaemia.
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Why may a patient with methadone overdose need repeated naloxone doses or an infusion?
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Naloxone's duration of action is shorter than that of many opioids, so respiratory depression can return.
Why? Opioid overdose triad: pinpoint pupils, respiratory depression and reduced consciousness.
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Why is flumazenil not routinely given in suspected benzodiazepine overdose?
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It can precipitate seizures, especially in benzodiazepine-dependent patients or after mixed overdose with tricyclics.
Why? Most benzodiazepine overdoses do well with supportive care alone.
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Which metabolic complication of quinine toxicity must be checked for?
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Hypoglycaemia (quinine stimulates insulin release).
Why? Quinine toxicity (cinchonism) causes tinnitus, deafness, headache and visual disturbance; severe toxicity causes QT prolongation, arrhythmias and blindness.
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What is the antidote for severe iron poisoning?
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IV desferrioxamine.
Why? Desferrioxamine chelates iron; the complex is excreted renally and can turn urine orange-red.
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A 58-year-old woman on lithium becomes dehydrated with gastroenteritis. She has a coarse tremor, ataxia and confusion, and then has a seizure. Her lithium level is 4.2 mmol/L and her creatinine is rising. What is the treatment of choice?
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Haemodialysis (stop lithium; IV fluids alone are for mild–moderate toxicity).
Why? Lithium is a small, water-soluble ion with low protein binding, so it is well removed by dialysis. Severe neurological features or renal impairment are indications.
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Which IV acetylcysteine regimen do RCEM and the National Poisons Information Service recommend as standard for paracetamol overdose in UK emergency departments?
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The 12-hour SNAP regimen: 100 mg/kg over 2 hours, then 200 mg/kg over 10 hours.
Why? SNAP gives the same total dose as the 21-hour three-bag regimen, works as well, and causes fewer anaphylactoid reactions. Treatment may need to continue after the second bag depending on bloods.
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A patient's 4-hour paracetamol level is below the treatment line, but the ALT is above the upper limit of normal. Should acetylcysteine be given?
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Yes — treat if blood tests suggest acute liver injury (ALT above the upper limit of normal or INR above 1.3, with no other cause), even when the level is below the line.
Why? A raised ALT or INR means liver injury may already be happening, so the nomogram alone cannot be relied on.
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