How to manage bradycardia caused by excessive metoprolol (beta blocker)?

Management of Bradycardia from Metoprolol Overdose

For patients with bradycardia due to excessive metoprolol, immediate discontinuation of metoprolol and implementation of supportive measures including vasopressors (norepinephrine or dopamine), glucagon administration, and high-dose insulin-euglycemia therapy are recommended as the most effective interventions. 1, 2

Initial Assessment and Management

• Immediately discontinue metoprolol to prevent further beta-blockade effects 2
• Monitor heart rate, blood pressure, and ECG continuously 1
• Assess for signs of hypoperfusion, altered mental status, or cardiogenic shock 2
• Secure IV access for administration of medications 1

First-Line Interventions

Vasopressor Support

• Administer norepinephrine or dopamine for hypotension 2
• Titrate to maintain adequate blood pressure and tissue perfusion 1

Glucagon Administration

• Administer glucagon 3-10 mg IV slowly over 3-5 minutes, followed by infusion of 3-5 mg/hour 1
• Glucagon works by activating adenylyl cyclase through a non-beta receptor mechanism, bypassing the blocked beta receptors 1
• Ensure airway protection before administration as glucagon commonly causes vomiting 1

Second-Line Interventions

High-Dose Insulin-Euglycemia Therapy

• Administer 1 U/kg regular insulin as IV bolus with 0.5 g/kg dextrose 1
• Continue infusion at 0.5-1 U/kg/hour of insulin and 0.5 g/kg/hour of dextrose 1
• Monitor serum glucose every 15-30 minutes initially, then every 1-2 hours once stable 1
• Target glucose levels of 100-250 mg/dL (5.5-14 mmol/L) 1
• Monitor potassium levels; moderate hypokalemia (2.5-2.8 mEq/L) is acceptable during this therapy 1

Calcium Administration

• Consider IV calcium in refractory cases 1
• Administer 0.3 mEq/kg of calcium (0.6 mL/kg of 10% calcium gluconate or 0.2 mL/kg of 10% calcium chloride) over 5-10 minutes 1
• Follow with infusion of 0.3 mEq/kg/hour, titrated to hemodynamic response 1
• Monitor ionized calcium levels to avoid severe hypercalcemia 1

Severe Cases/Refractory Bradycardia

Intravenous Lipid Emulsion (ILE)

• Consider ILE therapy in life-threatening metoprolol overdose 3
• Case reports show successful resuscitation with ILE combined with high-dose insulin-euglycemia therapy in severe metoprolol toxicity 3

Cardiac Support

• For cardiac failure, consider administration of a digitalis glycoside and diuretic 2
• For inadequate cardiac contractility, consider dobutamine, isoproterenol, or additional glucagon 2
• In extreme cases, mechanical circulatory support may be necessary 1

Special Considerations

Sex-Based Differences

• Women may be more susceptible to metoprolol-induced bradycardia than men at the same plasma concentrations 4
• Women show a stronger association between metoprolol concentration and heart rate reduction 4
• Consider this when determining the severity of overdose and response to treatment 4

Formulation Considerations

• Immediate-release (IR) metoprolol is associated with nearly twice the risk of emergent bradycardia compared to slow-release (SR) formulations 5
• This may influence the expected duration of toxicity and required monitoring period 5

Drug Interactions

• Check for concurrent medications that may potentiate metoprolol toxicity, particularly CYP2D6 inhibitors 6
• Medications like terbinafine can significantly increase metoprolol levels by inhibiting metabolism 6

Prevention of Recurrence

• When restarting beta-blocker therapy after resolution, consider:
  • Using a different beta-blocker with less bradycardia potential 7
  • Starting at a lower dose with gradual titration 1
  • More frequent monitoring of heart rate and symptoms 1
  • Avoiding drug interactions that increase metoprolol levels 6

Pitfalls to Avoid

• Do not abruptly discontinue beta-blockers in patients with coronary artery disease after resolution of bradycardia; taper gradually over 1-2 weeks 2
• Avoid aggressive potassium repletion during insulin-euglycemia therapy as it may lead to asystole 1
• Do not delay treatment while waiting for metoprolol levels; treatment decisions should be based on clinical presentation 3
• Be cautious with atropine as it may have limited effectiveness in severe beta-blocker overdose 3