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Beta-blocker poisoning is one of the classic cardiovascular-drug overdoses, and it is dangerous precisely because it looks like a simple bradycardia at first and then refuses to respond to the algorithm. A patient arrives after taking a bottle of metoprolol, propranolol, or carvedilol — sometimes a deliberate ingestion, sometimes an accidental double-up in an elderly patient with renal decline — and the monitor shows a heart rate in the 30s or 40s with a pressure to match. The reflex is to give atropine and move on. In a real beta-blocker overdose that reflex usually fails, and the nurse who understands why is the one who escalates before the patient codes.
Beta-adrenergic receptors are the heart's accelerator pedal. Beta-1 stimulation raises heart rate (chronotropy), contractile force (inotropy), and conduction speed through the AV node (dromotropy). Beta-blockers occupy those receptors, so in overdose the accelerator is pinned to the floor in the off position: the sinus node fires slowly, the ventricle squeezes weakly, and the AV node conducts sluggishly, which is why heart block can appear. The net result is a low heart rate multiplied by a low stroke volume — profound low cardiac output shock.
Not all beta-blockers behave identically in overdose, and that matters at the bedside. Propranolol is the worst actor: it is lipophilic, crosses into the brain to cause seizures and coma, and has membrane-stabilizing (sodium-channel-blocking) activity that widens the QRS and looks like a tricyclic overdose. Sotalol blocks potassium channels and prolongs the QT, setting up torsades. Highly beta-1-selective agents like metoprolol and atenolol can lose their selectivity at toxic doses. Knowing which agent was taken tells you whether to also watch for a widening QRS, a lengthening QT, or CNS depression.
The presenting picture is bradycardia, hypotension, and signs of low output: cool skin, altered mental status, and rising lactate. Beta-blocker and calcium-channel-blocker overdose look nearly identical on the monitor, and the initial resuscitation overlaps heavily, so you often treat them the same before you know which one it is. Two clues help separate them. Blood glucose tends to be normal or low in beta-blocker overdose (beta blockade impairs the glucose-raising stress response), whereas calcium-channel-blocker overdose classically causes hyperglycemia because the toxin blocks insulin release from the pancreas. Mental status is often more preserved in calcium-channel-blocker overdose until very late, while lipophilic beta-blockers like propranolol depress the CNS early.
Management stacks therapies rather than trying them one at a time and waiting. Airway and breathing come first, especially with propranolol's seizure and coma risk. Then the circulation gets a layered approach.
Glucagon raises heart rate and contractility through a receptor separate from the beta receptor, which is exactly why it works when catecholamines don't — it is the classic "bypass the blockade" drug. It is given as a bolus and then an infusion. The catch every nurse should anticipate: glucagon reliably causes vomiting, so airway protection and an antiemetic matter, and the hospital pharmacy may struggle to supply the large doses a real overdose needs.
This is the cornerstone of modern cardiotoxic-overdose care and is detailed in our dedicated high-dose insulin euglycemia guide. In brief, the poisoned heart cannot use fatty acids well and becomes dependent on glucose, and very large doses of insulin (far beyond diabetic dosing) improve cardiac contractility and metabolism. It requires an insulin bolus followed by a high-rate infusion, aggressive dextrose to keep the patient euglycemic, and relentless monitoring of glucose and potassium.
Calcium is given (more central to calcium-channel-blocker overdose but often used in both). High-dose vasopressors — norepinephrine, epinephrine — are titrated even though blunted, because some effect is better than none. Refractory cases escalate to intravenous lipid emulsion (a "lipid sink" that pulls lipophilic drug out of tissue, most useful for propranolol), transvenous pacing (which frequently fails to capture in severe poisoning), and ultimately mechanical circulatory support such as ECMO, which buys time for the drug to clear. For sotalol, magnesium and management of the prolonged QT and torsades take priority.
Once high-dose insulin is running, the nurse essentially becomes a metabolic-titration engine. Glucose must be checked frequently (often every 20–30 minutes early) because the insulin doses are enormous and hypoglycemia is a real, dangerous risk even with a dextrose infusion running. Potassium falls as insulin drives it intracellularly; it needs monitoring and cautious replacement, keeping in mind the guardrails in our IV potassium replacement guide and the fact that some hypokalemia here is a shift, not a true deficit. Watch for the fluid volume that accumulates from the dextrose carrier, and keep the glucagon-driven vomiting from becoming an aspiration event. Continuous telemetry, an arterial line, and serial lactates track whether the layered therapy is restoring perfusion.
Decontamination and enhanced elimination have limited but real roles: activated charcoal if the airway is protected and the ingestion is recent, and — for the water-soluble, renally cleared agents like atenolol and sotalol — hemodialysis can remove drug, which is not true for the highly protein-bound lipophilic agents.
Beta-blocker overdose is a bradycardic, low-output shock that mocks the standard bradycardia algorithm because the problem is a blockaded receptor, not an excess of vagal tone. The wins come from going around the blockade — glucagon and high-dose insulin above all, with calcium, vasopressors, lipid emulsion, and mechanical support layered underneath. For the ICU nurse, recognizing the refractory pattern early, anticipating the glucagon vomiting, and running the glucose-and-potassium tightrope of high-dose insulin are the differences between a save and a slow-motion arrest. When the QRS widens or the QT stretches, remember the agent-specific traps — propranolol's membrane effect and sotalol's torsades — and treat those on their own tracks.
Related: Calcium-channel-blocker overdose | High-dose insulin euglycemia | Digoxin toxicity | Unstable bradycardia | Tricyclic overdose
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