How should a metoprolol overdose be managed?

Management of Metoprolol Overdose

For metoprolol overdose with refractory shock, initiate high-dose insulin with glucose and IV glucagon as first-line antidotal therapies, with ECMO as rescue therapy for pharmacologically refractory cases 1.

Initial Stabilization and Supportive Care

Begin with standard BLS and ACLS protocols if cardiac arrest occurs 2. The primary manifestations you'll encounter are:

• Bradycardia (often severe, refractory to atropine)
• Hypotension (due to myocardial depression and vasodilation)
• Cardiogenic shock (from severe β-receptor blockade)
• Potential cardiac arrest (typically presenting as PEA or asystole)

Symptoms typically appear within 2 hours of ingestion for immediate-release formulations, but may be delayed up to 8 hours for sustained-release preparations 3.

Critical Pitfall

Metoprolol's moderate lipophilicity means it can cross the blood-brain barrier, potentially causing CNS depression, delirium, or seizures—don't attribute altered mental status solely to hypoperfusion 3.

Gastrointestinal Decontamination

Consider activated charcoal if the patient presents within 1-2 hours of ingestion and the airway can be protected 4. Gastric lavage has limited evidence but may be considered in massive, recent ingestions 4. However, these interventions are typically used alongside other therapies, making their independent contribution to survival difficult to assess.

Pharmacological Management Algorithm

Step 1: Standard Vasopressors and Inotropes

Start with catecholamines (norepinephrine, dopamine, or dobutamine) as initial therapy 5, 4. These provide survival benefit and hemodynamic improvement, though high-dose β-blocker toxicity may render them less effective due to receptor blockade 2.

Step 2: Antidotal Therapies (Class 2a Recommendations)

High-Dose Insulin Euglycemic Therapy (HIET) - This is reasonable as first-line antidotal therapy 1:

• Bolus: 1 U/kg regular insulin IV
• Infusion: 1 U/kg/hour, titrated to clinical effect (range 0.5-10 U/kg/hour reported)
• Concurrent dextrose: 0.5 g/kg bolus, then 0.5 g/kg/hour infusion
• Target glucose: 100-250 mg/dL (5.5-14 mmol/L)
• Monitor glucose: Every 15 minutes initially during titration 2
• Potassium monitoring: Target 2.5-2.8 mEq/L (avoid aggressive repletion—can cause asystole) 2

The mechanism involves improving myocardial energy utilization and contractility. Case reports demonstrate clear hemodynamic improvement, including survival from massive metoprolol overdose 2, 6.

IV Glucagon - Also reasonable as first-line therapy 1:

• Bolus: 3-10 mg (0.05-0.15 mg/kg) IV over 3-5 minutes
• Infusion: 3-5 mg/hour (0.05-0.10 mg/kg/hour), titrated to hemodynamic response 2
• Supply planning: May require >100 mg over 24 hours—secure adequate supply early 2
• Airway protection: Glucagon commonly causes vomiting; protect airway before administration in obtunded patients 2

Step 3: Calcium (Class 2b Recommendation)

IV Calcium may be considered in refractory shock 1:

• Dose: 0.3 mEq/kg (0.6 mL/kg of 10% calcium gluconate OR 0.2 mL/kg of 10% calcium chloride) over 5-10 minutes
• Infusion: 0.3 mEq/kg/hour, titrated to response 2
• Monitoring: Check ionized calcium levels; avoid severe hypercalcemia (>2× upper limit of normal) 2

Evidence is limited to animal studies and case reports, with variable efficacy 1, 2.

Adjunctive Therapies

Intravenous Lipid Emulsion (ILE): Variable response reported in case series 4, 6. Consider in life-threatening cases unresponsive to other therapies. One case demonstrated immediate return of spontaneous circulation when combined with HIET during cardiac arrest 6.

Atropine: May provide temporary improvement in heart rate but often ineffective in severe overdose 4.

Extracorporeal Support (Class 2b Recommendation)

Veno-Arterial ECMO (VA-ECMO) might be considered for shock refractory to all pharmacological therapy 1:

• Associated with improved survival in observational studies and case series 1, 4
• Provides hemodynamic bridge to recovery while drug is metabolized 7, 8, 9
• Consider early in massive overdoses given metoprolol's elimination half-life

Hemodialysis: Limited utility for metoprolol due to high protein binding and large volume of distribution 3. May assist with water-soluble β-blockers like atenolol but not specifically beneficial for metoprolol 4.

Key Monitoring Parameters

• Continuous cardiac monitoring: Heart rate, rhythm, blood pressure
• Frequent glucose checks: Every 15 minutes during HIET initiation, then hourly
• Electrolytes: Potassium every 1-2 hours during HIET (target 2.5-2.8 mEq/L)
• Ionized calcium: If calcium therapy used
• Lactate: Marker of tissue perfusion and shock severity
• Duration of observation: Minimum 6-8 hours for sustained-release formulations if asymptomatic 3

Critical Contraindications and Warnings

• Do NOT use flumazenil if benzodiazepine co-ingestion suspected—not indicated for β-blocker toxicity
• Central venous access required for concentrated dextrose solutions (>10%) and calcium infusions 2
• Avoid aggressive potassium repletion during HIET—associated with asystole in animal studies 2
• Multiple therapies often needed simultaneously—the evidence base consists primarily of case reports where patients received combination therapy, making it difficult to isolate individual treatment effects 4