Atenolol to Metoprolol Conversion
For dose conversion from atenolol to metoprolol, use a 1:1 ratio for immediate-release metoprolol tartrate (e.g., atenolol 50 mg once daily converts to metoprolol tartrate 50 mg twice daily), recognizing that metoprolol requires twice-daily dosing due to its shorter half-life. 1, 2, 3
Conversion Ratios Based on Pharmacokinetic Evidence
Milligram-for-milligram equivalence:
- Atenolol 100 mg once daily = Metoprolol tartrate 100 mg twice daily for equivalent 24-hour cardiovascular blockade 2, 4
- Atenolol 50 mg once daily = Metoprolol tartrate 50 mg twice daily for blood pressure control 1, 3
The key distinction is that atenolol's longer half-life allows once-daily dosing, while metoprolol tartrate's shorter half-life necessitates twice-daily administration to maintain consistent 24-hour beta-blockade 4. Studies demonstrate that metoprolol loses effectiveness 25 hours after a single dose, whereas atenolol maintains blood pressure and heart rate reduction throughout the 24-hour period 4.
Alternative: Extended-Release Metoprolol Succinate
For once-daily dosing convenience, metoprolol succinate (extended-release) provides superior 24-hour coverage:
- Atenolol 50-100 mg once daily = Metoprolol succinate 50-100 mg once daily 5
- Metoprolol succinate demonstrates better early morning blood pressure control (12 AM-6 AM) compared to atenolol, with systolic BP reductions of -7±8 mmHg vs 3±14 mmHg respectively 5
- Overall 24-hour systolic BP control is superior with metoprolol succinate (-9±11 mmHg) versus atenolol (1±15 mmHg) 5
Dosing Recommendations by Indication
For hypertension:
- Start metoprolol tartrate 25-50 mg twice daily or metoprolol succinate 50-100 mg once daily 6
- Maximum dose: metoprolol tartrate 200 mg daily, metoprolol succinate 400 mg daily 6
For atrial fibrillation rate control:
- Metoprolol tartrate 25-100 mg twice daily or metoprolol succinate 50-400 mg once daily 7
- Target resting heart rate <80 bpm for symptomatic management 7
For heart failure with reduced ejection fraction:
- Start metoprolol succinate 12.5-25 mg once daily, titrate to target dose of 200 mg once daily 6
Critical Monitoring During Conversion
Check the following before and after conversion:
- Heart rate (hold if <50 bpm with symptoms or <45 bpm consistently) 6
- Blood pressure (hold if systolic <100 mmHg with symptoms) 6
- Signs of decompensated heart failure (new or worsening dyspnea, edema, rales) 6
- Bronchospasm in patients with reactive airway disease 6
Common Pitfalls to Avoid
Do not assume 1:1 conversion with once-daily dosing for immediate-release metoprolol - this will result in inadequate 24-hour coverage, particularly in the early morning hours when cardiovascular risk is highest 4, 5. The shorter half-life of metoprolol tartrate (3-7 hours) compared to atenolol (6-9 hours) necessitates twice-daily administration 4.
Avoid abrupt discontinuation of atenolol before starting metoprolol - beta-blocker withdrawal carries a 2.7-fold increased risk of 1-year mortality and can precipitate severe angina exacerbation, myocardial infarction, and ventricular arrhythmias 6. Start metoprolol immediately after the last atenolol dose.
Do not convert patients with active contraindications including decompensated heart failure, heart rate <50 bpm, second or third-degree heart block, active asthma, or systolic blood pressure <100 mmHg 6.