What is the equivalent dose of propranolol (propranolol) LA for a patient currently taking metoprolol (metoprolol) ER 100 mg?

Beta-Blocker Conversion: Metoprolol ER to Propranolol LA

Convert metoprolol ER 100 mg daily to propranolol LA 80-160 mg daily, starting at 80 mg once daily and titrating based on heart rate and blood pressure response.

Direct Conversion Strategy

There is no established equipotent dose conversion between metoprolol and propranolol because they differ in beta-1 selectivity, lipophilicity, and pharmacokinetics. However, based on guideline-recommended dosing ranges, a practical conversion approach can be outlined:

Starting Dose Recommendation

• Begin with propranolol LA 80 mg once daily 1, 2
• This represents a conservative starting point within the therapeutic range for most indications 1, 2
• Metoprolol ER 100 mg is a low-to-moderate dose, so starting propranolol at the lower end of its range (80 mg) minimizes risk of excessive beta-blockade 1, 3

Titration Protocol

• Increase to propranolol LA 120-160 mg once daily if heart rate control or blood pressure targets are not achieved after 1-2 weeks 1, 2
• The typical maintenance range for propranolol LA is 80-160 mg daily for hypertension and rate control 1, 2
• Maximum dose can reach 240 mg daily if needed, though most patients respond to 80-160 mg 1

Pharmacological Rationale

Key Differences Between Medications

• Metoprolol is beta-1 selective (cardioselective), while propranolol is non-selective (blocks both beta-1 and beta-2 receptors) 1, 3
• Propranolol has greater lipophilicity and crosses the blood-brain barrier more readily, potentially causing more CNS side effects 3
• Both medications require gradual dose adjustments rather than direct milligram-for-milligram conversion 1, 3

Bioequivalence Considerations

• A 100 mg metoprolol ER tablet contains 95 mg metoprolol succinate and is considered equivalent to 100 mg metoprolol tartrate 4
• Propranolol immediate-release 80-160 mg daily (divided doses) converts to propranolol LA 80-160 mg once daily 5
• The lack of direct conversion tables in guidelines reflects the need for individualized titration based on clinical response 1

Critical Safety Considerations Before Switching

Mandatory Pre-Switch Assessment

• Check for contraindications specific to propranolol that may not apply to metoprolol 1, 2:
  • Asthma or obstructive airway disease (propranolol is non-selective and blocks beta-2 receptors) 1, 2
  • Second or third-degree heart block 1, 2
  • Decompensated heart failure 1, 2
  • Diabetes with history of hypoglycemic episodes (propranolol masks hypoglycemia symptoms more than metoprolol) 6, 7

Switching Protocol

• Do not abruptly discontinue metoprolol - switch directly from metoprolol ER to propranolol LA on the same day to avoid rebound hypertension or tachycardia 3, 5
• Take the first dose of propranolol LA on the morning after the last dose of metoprolol ER 5
• Monitor heart rate and blood pressure within 1-2 weeks after switching 3, 5

Monitoring Parameters Post-Conversion

Initial Monitoring (First 2-4 Weeks)

• Heart rate: Target resting heart rate 50-80 bpm depending on indication 3
• Blood pressure: Target <130/80 mmHg for hypertension 1
• Symptoms: Watch for excessive bradycardia, hypotension, bronchospasm, or worsening heart failure 1, 2

Specific Adverse Effects to Monitor

• Bronchospasm (more common with propranolol than metoprolol due to beta-2 blockade) 1, 2
• Hypoglycemia masking in diabetic patients (propranolol blocks both beta-1 and beta-2 receptors involved in glucose recovery) 6, 7
• CNS effects such as fatigue, dizziness, or sleep disturbances (propranolol is more lipophilic) 2

Common Pitfalls to Avoid

• Do not assume 1:1 dose equivalence - metoprolol 100 mg does not equal propranolol 100 mg 1, 3
• Do not use propranolol in patients with reactive airway disease - metoprolol's beta-1 selectivity is lost with propranolol 1, 2
• Do not abruptly stop either medication - both require gradual tapering if discontinuation is needed 3, 8
• Do not combine propranolol with non-dihydropyridine calcium channel blockers (diltiazem, verapamil) due to increased bradycardia and heart block risk 1, 2

Alternative Dosing for Specific Indications

For Atrial Fibrillation Rate Control

• Start propranolol LA 80 mg once daily, titrate to 80-160 mg daily 1
• Target resting heart rate <80-110 bpm depending on rate control strategy 3

For Hypertension

• Start propranolol LA 80 mg once daily, titrate to 120-160 mg daily 1, 2
• Some patients may require up to 240 mg daily 1

For Migraine Prophylaxis or Anxiety

• Propranolol LA 80-160 mg once daily is typical 2
• For situational anxiety, immediate-release propranolol 10-40 mg as needed may be more appropriate than LA formulation 2