Beta-blockers

Mechanism of toxicity
Toxic dose
Symptoms and signs of poisoning
Management
Symptomatic and supportive
Monitoring

Mechanism of toxicity

Blocks β1-adrenoreceptors (reduce heart rate and contractility) and β2-adrenoreceptors (hypotension) and stabilises myocardial cell membranes (ventricular arrhythmias).

Toxic dose

Depends on particular β-blocker and the patient’s underlying morbidity.

Symptoms and signs of poisoning

• Cardiovascular: bradycardia (early feature), hypotension (early feature), QRS widening and arrhythmias.
• Neurological: depressed level of consciousness, seizures (high risk if QRS ≥ 100 milliseconds).
• Respiratory: respiratory depression, bronchoconstriction.
• Endocrine: hypoglycaemia (children).

Management

Note general principles of acute poisoning.

Symptomatic and supportive

• Hypotension: IV crystalloid.
  • Options for refractory hypotension:
  • IV glucagon: 5mg bolus, if no response after 5 minutes: 10 mg bolus. Responders: continuous infusion in the same bolus amount (5 or 10 mg/hour).
    • IV high-dose insulin and glucose: 50 mL of 50% dextrose IV and bolus of 1 unit/kg short-acting insulin, followed by 0.5 units/kg/hr titrated up until systolic BP 90 mmHg (max. 2 units/kg). Continuous monitoring and correction of hypoglycaemia and hypokalaemia.
    • IV vasopressor (e.g. dopamine or adrenalin).
    • IV calcium salts (calcium gluconate: 30 to 60 mL of 10% solution; calcium chloride: 10 to 20 mL of 10% solution), can be repeated every 5 minutes up to 4 doses. Responders: infusion 1-2 g/hour.
• Bradycardia: Atropine 0.5-1.0mg IV every 2-3 minutes (max. 3mg).
• Complete heart block: consider pacing.

Monitoring

• Cardiovascular: ECG, heart rate, blood pressure.
• Blood glucose in children.