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Q1: Mechanism and clinical recognition (3 min)
Examiner: A patient presents four hours after taking an overdose of verapamil with bradycardia, hypotension and a blood glucose of 14 mmol/L. Walk me through the mechanism and why this points to a calcium-channel blocker rather than a beta-blocker.
Expected answer:
- Verapamil is a non-dihydropyridine CCB that directly blocks the L-type voltage-gated calcium channel. In the SA and AV nodes this channel carries the slow inward calcium current responsible for the upstroke (phase 0) — blockade produces bradycardia and AV block. In working myocytes, reduced plateau-phase calcium entry weakens excitation-contraction coupling -> negative inotropy and cardiogenic shock.
- The hyperglycaemia is the discriminator: L-type calcium channels on pancreatic beta cells mediate the calcium influx that triggers insulin granule exocytosis; verapamil blocks this -> impaired insulin release -> hyperglycaemia. A beta-blocker overdose does NOT cause hyperglycaemia (and may cause hypoglycaemia).
- The metabolic/lactic acidosis is from impaired cardiac carbohydrate metabolism and shock.
- Four-hour delay to severe toxicity suggests a sustained-release preparation.
Follow-up: Why does standard ACLS (atropine, adrenaline) often fail? The channel is directly blocked downstream of vagal tone and beta-receptor stimulation — you need calcium, HIET, lipid, ECMO.
Q2: The lethal subtype (3 min)
Examiner: Why is sustained-release verapamil the most lethal prescription overdose, and what does that mean for your management?
Expected answer:
- Sustained-release verapamil/diltiazem have a deceptive latent phase (6-12 h, sometimes up to 24 h) during which the patient can look well, followed by sudden refractory cardiovascular collapse — a biphasic course.
- The delayed absorption means toxicity continues to develop and recur; small numbers of tablets are lethal; reported mortality up to 20-30 per cent in severe series.
- Management implications: mandatory 24 h ICU admission even if initially well, whole-bowel irrigation with polyethylene glycol to remove the slow-release tablets, early and prolonged HIET, low threshold for VA-ECMO.
- Do NOT be reassured by the well-appearing patient.
Q3: Management ladder with drug doses (4 min)
Examiner: Take me through the management of severe BB/CCB overdose with specific drug doses.
Expected answer — stepwise ladder:
- ABCDE — airway (intubate early if GCS depressed), oxygen, two large-bore IV cannulae, continuous cardiac monitoring. Cautious fluids (250-500 mL aliquots — myocardium failing). Check and treat hypoglycaemia.
- Decontamination — activated charcoal 50 g within 1-2 h (airway protected); whole-bowel irrigation (polyethylene glycol 1-2 L/h) for sustained-release.
- Atropine 0.5-1 mg IV every 3-5 min up to 3 mg — often ineffective; do not delay.
- IV CALCIUM — calcium chloride 10% 10-20 mL (1 g) via central line, OR calcium gluconate 10% 30-60 mL via peripheral line; repeat every 10-20 min then infusion. Overcomes channel blockade.
- HIET (most effective) — insulin 1 U/kg IV bolus then 0.5-1 U/kg/h (up to 10 U/kg/h severe) + dextrose (25 g bolus then 0.5-1 g/kg/h, keep glucose 5-10); supplement K+ to above 2.5-2.8 mmol/L. Onset 15-45 min; continue 12-24 h after stability then wean.
- Glucagon (for BB) 5-10 mg IV then 1-5 mg/h — bypasses the blocked beta-receptor; causes vomiting.
- Vasopressors — noradrenaline and/or adrenaline, high-dose, often combined.
- Lipid emulsion 20% 1.5 mL/kg bolus then 0.25 mL/kg/min — refractory, lipophilic drugs.
- Pacing for refractory bradycardia.
- VA-ECMO for refractory cardiogenic shock — bridge to drug clearance.
Follow-up — mechanism of HIET: the poisoned myocardium is in carbohydrate-metabolism failure (shifts to inefficient fatty-acid oxidation). HIET shifts cardiac metabolism back toward more efficient glucose oxidation (more ATP per oxygen) and provides positive inotropy independent of the blocked receptor/channel.
Q4: Special agents — sotalol and propranolol (2 min)
Examiner: How does the management differ for sotalol and propranolol overdose?
Sotalol:
- Non-selective beta-blocker that ALSO blocks the delayed-rectifier potassium channel (I_Kr) -> long QT -> torsades de pointes.
- Treat the torsades with IV magnesium sulphate 2 g, correction of K+/Mg2+, and isoprenaline infusion or overdrive pacing to shorten the QT by increasing heart rate.
- AVOID other QT-prolonging drugs. Half-life 12-16 h so prolonged monitoring.
Propranolol:
- Most lipophilic beta-blocker; crosses the BBB; at high concentration exerts membrane-stabilising (fast Na-channel) effect -> seizures, coma, QRS widening (resembles TCA toxicity).
- Treat seizures with benzodiazepines; give sodium bicarbonate for QRS widening (as in TCA toxicity); lipid emulsion for refractory collapse (propranolol is highly lipophilic — the 'lipid sink').
Q5: Pitfalls and disposition (2 min)
Examiner: What are the classic pitfalls, and how do you decide on disposition?
Pitfalls:
- Being reassured by the well-appearing sustained-release verapamil patient who later collapses — admit for 24 h.
- Relying on atropine alone — it is often ineffective.
- Under-dosing calcium, insulin and vasopressors — high-dose combination therapy is expected.
- Omitting whole-bowel irrigation for sustained-release.
- Failing to check and treat glucose (BB hypoglycaemia) and potassium (HIET-induced hypokalaemia).
- Late referral for ECMO.
- Missing co-ingestants (digoxin, TCA, paracetamol).
- Rebound/recrudescence after apparent stabilisation — wean HIET/pressors slowly.
Disposition:
- Sustained-release ingestion: ICU for at least 24 h regardless of initial appearance.
- Immediate-release: observe 6 h; asymptomatic with normal ECG and haemodynamics may be discharged after psychiatric assessment; any symptom or ECG change -> admit.
- All deliberate overdoses need psychiatric assessment after medical stabilisation; paediatric accidental ingestion needs child-safeguarding review.