Beta Blocker Toxicity and Overdose

• Beta-adrenergic receptor antagonism: Beta blockers competitively inhibit catecholamine binding at β1-adrenergic receptors (predominantly on cardiac myocytes) and β2-adrenergic receptors (vascular smooth muscle, bronchial tissue), eliminating the inotropic and chronotropic effects of endogenous and exogenous catecholamines. This results in decreased cardiac contractility (negative inotropic effect), decreased heart rate (negative chronotropic effect), decreased atrioventricular (AV) nodal conduction velocity, and peripheral vasoconstriction, collectively reducing cardiac output and blood pressure.

• Membrane-stabilizing properties: Lipophilic beta blockers (particularly propranolol, carvedilol, and labetalol) possess quinidine-like membrane-stabilizing effects through inhibition of fast sodium channels, prolonging action potential duration and slowing electrical conduction throughout the myocardium. This mechanism is independent of beta-receptor blockade and becomes clinically significant only at supratherapeutic concentrations, manifesting as QRS prolongation, QT prolongation, and increased risk of dysrhythmias including bradycardia-dependent torsades de pointes.

• Metabolic derangements: Unopposed alpha-adrenergic stimulation may cause vasoconstriction and hypertension in early overdose, but the predominant effect is severe hypoglycemia due to blocked beta2-mediated hepatic glycogenolysis and impaired gluconeogenesis in the setting of catecholamine deficiency; additionally, beta blockers impair the normal counterregulatory response to hypoglycemia. Hyperkalemia may develop through reduced cellular potassium uptake (normally beta2-mediated), particularly in patients with renal insufficiency or concurrent acidosis.

Major Causes

• Acute intentional overdose (suicidal ingestion): Most common cause in adolescents and adults; propranolol overdose carries highest mortality risk
• Accidental overdose or dosing error: Particularly in elderly patients with renal impairment or those on multiple medications
• Chronic toxicity: Supratherapeutic dosing for medical indications; progressive accumulation in patients with hepatic or renal dysfunction
• Drug interactions: Concurrent use of verapamil, diltiazem, or disopyramide potentiates cardiac depression; lipophilic beta blocker absorption increased by high-fat meals
• Ingestion of sustained-release formulations: Delayed onset (4–12 hours) and prolonged toxicity; multiple-dose activated charcoal may be indicated

Risk Factors for Severe Toxicity

• Advanced age: Reduced hepatic metabolism and compensatory mechanisms
• Renal impairment (eGFR <30 mL/min): Impaired renal excretion of hydrophilic metabolites
• Hepatic disease: Decreased hepatic metabolism of lipophilic agents
• Pre-existing conduction disease: Baseline AV block or sick sinus syndrome significantly worsens with beta blockade
• Cardiomyopathy or left ventricular dysfunction: Limited cardiac reserve to tolerate negative inotropic effects
• Hypoglycemia or diabetes mellitus: Impaired counterregulatory response
• Lipophilic agent use: Propranolol, labetalol, carvedilol cause more severe toxicity than hydrophilic agents like atenolol or nadolol

Early Signs (onset 30 minutes to 4 hours)

• Bradycardia (most common finding; may be severe with rates <40 bpm)
• Hypotension (often refractory to standard measures)
• Lightheadedness, syncope, or presyncope: Due to decreased cerebral perfusion
• Fatigue and malaise

Cardiovascular Manifestations

• Cardiogenic shock with decreased cardiac output and end-organ hypoperfusion
• Conduction abnormalities: First-degree AV block, second-degree (Wenckebach) AV block, complete heart block
• Bradyarrhythmias: Junctional rhythm, asystole
• Hypotension unresponsive to standard vasopressors (defining feature in severe toxicity)
• Pulmonary edema in patients with underlying cardiomyopathy due to negative inotropic effect

Metabolic & Neurological Effects

• Severe hypoglycemia (often refractory to glucose administration due to blocked gluconeogenesis); may present with altered mental status, seizures, or coma without warning signs
• Seizures: May be provoked by hypoglycemia, cerebral hypoperfusion, or toxicity itself (especially propranolol)
• Altered mental status, confusion, or coma: From cerebral hypoperfusion or hypoglycemia; propranolol crosses blood-brain barrier causing CNS effects
• Bronchospasm: May occur, particularly in those with asthma or COPD (beta2-blockade)

Physical Examination Findings

• Bradypnea with depressed mental status
• Cyanosis or pallor
• Cool, clammy extremities indicating peripheral hypoperfusion
• Pulmonary crackles if pulmonary edema present
• Diaphoresis (early compensatory response)

Clinical Diagnosis

Electrocardiography (Essential)

• Bradycardia with regular rhythm
• QRS prolongation (>120 ms) and QT prolongation: Indicates membrane-stabilizing effects (propranolol, carvedilol, labetalol)
• AV block: First-degree (prolonged PR interval), second-degree (Wenckebach pattern most common), or third-degree (complete heart block)
• Junctional rhythm or asystole in severe toxicity
• ST-segment changes may mimic myocardial infarction

Laboratory Studies

• Serum glucose: Hypoglycemia often profound and may not respond to dextrose alone
• Basic metabolic panel: Assess renal function, potassium (hyperkalemia may occur), sodium
• Arterial blood gas (ABG): Evaluate for metabolic acidosis (indicates shock and poor perfusion)
• Troponin and myoglobin: Rule out myocardial infarction or rhabdomyolysis
• Lactate: Elevated lactate indicates anaerobic metabolism and inadequate perfusion
• Liver function tests: Assess hepatic synthetic function
• Toxicology screen: Identifies co-ingested substances (opioids, sedatives, tricyclic antidepressants)
• Beta blocker levels: Not routinely available; not useful for acute management

Imaging

• Chest X-ray: Assess for pulmonary edema, aspiration
• Echocardiography: May reveal decreased cardiac function, wall motion abnormalities (if available and does not delay treatment)

Diagnostic Criteria

Supportive Care (Foundation of Management)

• Aggressive IV fluid resuscitation: Initiate with 20 mL/kg bolus of normal saline; continue cautiously while monitoring for pulmonary edema
• Decontamination: Activated charcoal (50–100 g) if patient presents within 1–2 hours of ingestion and airway is protected; consider multiple-dose activated charcoal for sustained-release formulations
• GI decontamination: Gastric lavage consideration if recent large ingestion; not routinely recommended due to aspiration risk
• Airway protection: Intubation if altered mental status, severe hypoglycemia, or seizures; use caution with induction agents (avoid propofol, which reduces blood pressure further)

Specific Antidotal Therapy (Critical for Severe Toxicity)

High-dose insulin euglycemic therapy (HIET) — First-line for severe bradycardia/hypotension

• Mechanism: Directly increases myocardial contractility and peripheral vascular resistance independent of beta-adrenergic signaling; improves glucose utilization
• Regimen:
• Initial bolus: 1 unit/kg regular IV insulin (max 10 units IV push)
• Continuous infusion: Start at 0.5–1 unit/kg/hour, titrate by 0.5 units/kg/hour every 5–10 minutes to achieve hemodynamic improvement (target systolic BP >90 mmHg, HR >60 bpm)
• May require 10–15 units/kg/hour in refractory cases
• Dextrose concurrent infusion: Start 50% dextrose at 0.5 g/kg/hour to maintain serum glucose 100–250 mg/dL (critical to prevent hypoglycemia during insulin infusion)
• Monitor serum potassium closely (insulin drives potassium intracellularly; give potassium supplementation if K <2.5 mEq/L)
• Continue until hemodynamic stability achieved and can transition to standard supportive care

Atropine (Limited efficacy but first-line for bradycardia alone)

• Dose: 0.5–1 mg IV push; repeat every 5 minutes to maximum 3–5 mg
• Mechanism: Blocks vagal acetylcholine effects on AV node, increasing heart rate
• Limitations: Often ineffective in severe beta blocker toxicity; does not address hypotension or negative inotropic effects
• Indication: Bradycardia with relative hemodynamic stability; not sole therapy in hypotensive patients

Vasopressors & Inotropes (Adjunctive therapy)

• Glucagon:
• Dose: 5–10 mg IV bolus, then 1–5 mg/hour infusion
• Mechanism: Activates adenylyl cyclase via G-protein coupling (bypasses beta-adrenergic receptor), increasing cAMP and myocardial contractility
• Limitations: Often less effective than high-dose insulin; tachyphylaxis develops with prolonged use; side effects include nausea, hyperglycemia
• Role: Can be used as adjunct to HIET; historically first-line but superseded by insulin
• Epinephrine:
• Dose: 0.1–0.5 mcg/kg/min IV infusion, titrate to effect
• Mechanism: Direct alpha- and beta-adrenergic agonism; may overcome beta blockade at high doses
• Advantage: Often effective in refractory cases
• Limitations: Higher doses required due to receptor antagonism by beta blocker
• Dopamine:
• Dose: 5–20 mcg/kg/min IV infusion
• Mechanism: Dose-dependent alpha- and beta-agonism; at higher doses predominantly alpha effects
• Role: Can be used but less effective than epinephrine in severe cases
• Isoproterenol: Rarely used due to risk of proarrhythmia; not recommended
• Vasopressin: May be added to epinephrine in refractory hypotension (0.04 units/min)

Calcium and Lipophilic Drug Sequestration

• Calcium chloride or gluconate:
• Dose: 10% calcium chloride 500–1000 mg (1–2 g IV push) or 10% calcium gluconate 1–2 g IV
• Mechanism: Improves myocardial contractility through inotropic effects; may partially overcome negative inotropic effects of beta blockade
• Evidence: Anecdotal benefit; not a primary treatment but reasonable adjunct
• Monitoring: Repeat every 10–20 minutes if response; monitor ionized calcium (goal <6–7 mg/dL above baseline to avoid hypercalcemia)

• Lipid emulsion therapy (20% lipid emulsion):
• Indication: Severe, refractory toxicity particularly with lipophilic agents (propranolol, carvedilol)
• Mechanism: Extracts lipophilic beta blocker from aqueous compartment into lipid phase, reducing free drug concentration at receptor sites
• Regimen: 20% lipid emulsion 1.5 mL/kg IV bolus over 1 minute, followed by infusion 0.25 mL/kg/min; escalate to 0.5 mL/kg/min if no response; maximum cumulative dose 10–12 mL/kg
• Contraindications: Relative contraindication in severe hypertriglyceridemia (>400 mg/dL)
• Evidence: Case reports and observational studies suggest benefit in refractory cases; not first-line but increasingly recognized as salvage therapy

Cardiac Pacing

• Indication: Complete heart block, severe bradycardia with symptoms refractory to pharmacotherapy
• Method: Transvenous pacing preferred if cardiogenic shock; transcutaneous pacing as temporizing measure (may be uncomfortable and unreliable)
• Note: Pacing increases rate but does not restore contractility; must be combined with pharmacotherapy

Seizure Management

• Benzodiazepines (lorazepam or diazepam): First-line; address both seizures and anxiety/agitation
• Phenytoin or fosphenytoin: Second-line if benzodiazepines ineffective
• Address underlying hypoglycemia: Often seizures terminate after glucose normalization and restoration of perfusion

Hemodialysis and Extracorporeal Support

• Hemodialysis: Effective for hydrophilic beta blockers (atenolol, nadolol, sotalol) with high water solubility and low protein binding; may remove 20–30% in 4–6 hours
• Indication: Renal failure, severe toxicity with hydrophilic agent, large ingestion
• Limitation: Less effective for lipophilic agents (propranolol, carvedilol) due to high protein binding
• Extracorporeal membrane oxygenation (ECMO) or cardiopulmonary bypass: Reserved for refractory cardiogenic shock unresponsive to maximal medical therapy; provides mechanical support while allowing time for drug metabolism and clearance
• Indication: Asystole, profound cardiogenic shock, cardiac arrest unresponsive to resuscitation

Monitoring During Treatment

• Continuous cardiac monitoring: Assess for dysrhythmias, bradycardia, AV block progression
• Serial vital signs: Target systolic BP >90 mmHg, HR >60 bpm
• Serum glucose: Check every 15–30 minutes during acute phase; maintain 100–250 mg/dL
• Serum electrolytes, particularly potassium: Check every 1–2 hours during insulin infusion
• Arterial or venous blood gas: Monitor for metabolic acidosis; improving lactate indicates adequate perfusion
• Chest X-ray: Assess for pulmonary edema progression
• **Ur

Complications of the toxicity itself

• Refractory cardiogenic shock (emergency): Combined loss of β1-mediated inotropy and chronotropy plus membrane-stabilizing sodium channel blockade drops cardiac output below the threshold for organ perfusion. Signaled by rising lactate, narrowing pulse pressure, cool mottled skin, and oliguria despite escalating catecholamines — the AHA 2023 scientific statement on cardiac arrest and life-threatening toxicity from poisoning frames this as the trigger to escalate to high-dose insulin and to consult for extracorporeal support (ECMO).
• Complete heart block, asystole, and PEA arrest (emergency): Progressive AV nodal and sinus node suppression; heralded on the monitor by lengthening PR interval, then a slow junctional escape rhythm.
• **Wide-QRS dysrhythmia with sotalol or *propranolol*** (emergency): *Sotalol*'s class III potassium channel blockade prolongs QT and causes bradycardia-dependent torsades de pointes, which can degenerate into the shockable pair — ventricular fibrillation / pulseless VT. *Propranolol*'s sodium channel blockade widens QRS and produces a monomorphic wide-complex rhythm resembling tricyclic toxicity.
• Seizures and coma (emergency): Lipophilic agents cross the blood–brain barrier; hypoglycemia and cerebral hypoperfusion compound it. Seizures in a bradycardic hypotensive patient should prompt an immediate glucose check.
• Bronchospasm in asthma/COPD from β2 blockade; end-organ injury — acute kidney injury, ischemic hepatitis, mesenteric ischemia — reflects shock duration.

Complications of treatment

• Hypoglycemia and hypokalemia from high-dose insulin: Insulin effect outlasts the infusion, so glucose can crash hours after weaning; potassium shifts intracellularly. Requires scheduled glucose and potassium monitoring well past discontinuation.
• Vomiting and aspiration from glucagon or from activated charcoal given to an obtunded patient (emergency); AACT/EAPCCT position statements restrict charcoal to a protected airway.
• Tissue necrosis from extravasated calcium chloride, digital/limb ischemia from high-dose vasopressors, and hypertriglyceridemia, pancreatitis, laboratory assay interference, and ECMO circuit fouling after lipid emulsion.
• Pacing failure to capture — and even when capture occurs, rate without contractility may not raise blood pressure.

• Glucose is the discriminator: bradycardia + hypotension + hypoglycemia points to beta blocker toxicity, whereas bradycardia + hypotension + hyperglycemia points to calcium channel blocker toxicity (blocked insulin release from pancreatic β-cell L-type calcium channels). This is the single association examiners test most.
• Diaphoresis is preserved in beta blocker–masked hypoglycemia: adrenergic warning symptoms (tremor, palpitations) are blunted, but sweating is cholinergically mediated and persists. A diabetic patient on a beta blocker with sweating and confusion is hypoglycemic.
• ***Propranolol* is the board's worst-case agent**: lipophilic + membrane-stabilizing → wide QRS, seizures, and coma. Wide QRS in this setting is treated like sodium channel blocker toxicity with IV sodium bicarbonate, consistent with the AHA 2023 poisoning scientific statement.
• ***Sotalol* is the odd one out**: class III potassium channel blockade → QT prolongation and bradycardia-dependent torsades. Best next steps are IV magnesium sulfate and overdrive pacing, not more atropine. Sotalol and atenolol are hydrophilic and dialyzable — the EXTRIP workgroup supports extracorporeal removal in severe sotalol or atenolol poisoning; propranolol and carvedilol are protein-bound and are not.
• Atropine first, but do not stop there: per the ACLS bradycardia algorithm it is the reflexive first drug, yet it fails in significant beta blockade because the lesion is receptor blockade, not vagal tone. The single best next step in shock is a vasoactive/antidotal strategy — high-dose insulin euglycemic therapy with concurrent dextrose, per this article's framing.
• Glucagon works downstream of the receptor (G-protein → adenylyl cyclase → cAMP), which is exactly why it is the mechanistic answer of choice on Step 1 even though tachyphylaxis and vomiting limit it clinically.
• Sustained-release ingestions need prolonged observation — onset may be delayed many hours, so an asymptomatic ECG at presentation does not permit discharge.
• Common distractors: isoproterenol (proarrhythmic), flumazenil or naloxone (wrong toxidrome), and "give more dextrose" alone for refractory hypoglycemia.