Equivalent Dosing: Atenolol vs Metoprolol Tartrate
For equivalent β-blockade, atenolol 100 mg once daily is approximately equivalent to metoprolol tartrate 100 mg twice daily (200 mg total daily dose), meaning metoprolol requires roughly twice the milligram dose of atenolol to achieve comparable cardiovascular effects.
Dose Equivalency Based on Guidelines and Research
The 2023 ACC/AHA/ACCP/HRS Atrial Fibrillation guideline 1 and 2017 ACC/AHA Hypertension guideline 2 provide the following dosing ranges:
- Atenolol: 25-100 mg once daily 1, 2
- Metoprolol tartrate: 25-200 mg twice daily (50-400 mg total daily) 1; 100-200 mg twice daily for hypertension 2
The FDA label for metoprolol tartrate 3 specifies usual starting doses of 100 mg daily in single or divided doses for hypertension, with effective ranges of 100-450 mg daily.
Evidence Supporting 1:2 Dose Ratio
The most definitive evidence comes from a 1981 study 4 demonstrating that atenolol 100 mg once daily, metoprolol 100 mg twice daily, and metoprolol 300 mg once daily produced equivalent β-adrenoceptor blockade over 24 hours. This clearly establishes that milligram-for-milligram, atenolol and metoprolol do not produce equivalent blockade.
Multiple comparative studies support this ratio:
- A 1984 study 5 found 100 mg atenolol once daily more effective than 100 mg metoprolol once daily, particularly at 25 hours post-dose, due to metoprolol's shorter half-life
- A 1982 asthma study 6 used "equipotent beta1-blocking doses" of atenolol 100 mg once daily and metoprolol 100 mg twice daily
- A 1981 hypertension trial 7 found atenolol and metoprolol equipotent at 100 mg once daily, but this likely reflects suboptimal metoprolol dosing given its shorter duration
Pharmacokinetic Rationale
The dose difference stems from fundamental pharmacokinetic differences 3:
Atenolol's longer half-life and renal elimination 1, 2 provide more sustained β-blockade with once-daily dosing. Metoprolol's shorter half-life necessitates twice-daily dosing and higher total daily doses to maintain 24-hour coverage.
Clinical Application Algorithm
For converting between agents:
- Atenolol 50 mg once daily → Metoprolol tartrate 50 mg twice daily (100 mg total)
- Atenolol 100 mg once daily → Metoprolol tartrate 100 mg twice daily (200 mg total)
Important caveats:
- Metoprolol tartrate requires twice-daily dosing for sustained effect; once-daily dosing results in inadequate 24-hour control 5
- For once-daily metoprolol dosing, use metoprolol succinate (extended-release) 50-200 mg daily 1, which has a 3-7 hour half-life but sustained release
- In renal impairment, atenolol requires no dose adjustment but accumulates with severe dysfunction; metoprolol may be preferred 3
- Both agents lose β1-selectivity at higher doses 3
Common Pitfall
Do not assume 1:1 dose equivalency. Using metoprolol tartrate 100 mg once daily instead of twice daily will result in inadequate β-blockade during the latter half of the dosing interval, particularly problematic for rate control or angina management.