From the Guidelines
The equivalent dose of propranolol to metoprolol 40 mg twice daily is approximately 80 mg of propranolol taken twice daily (160 mg total daily dose). When converting between these two beta-blockers, it's essential to understand that propranolol is less selective than metoprolol, meaning it blocks both beta-1 and beta-2 receptors more broadly. The conversion ratio is roughly 1:2, where 1 mg of metoprolol is equivalent to about 2 mg of propranolol in terms of beta-blocking potency, as seen in the dosing recommendations for various beta-blockers, including propranolol and metoprolol 1.
Some key points to consider when switching between these medications include:
- Monitoring patients for changes in heart rate, blood pressure, and any side effects
- The transition should ideally be gradual, starting with the equivalent dose and adjusting as needed based on clinical response
- Both medications work by blocking beta-adrenergic receptors, primarily in the heart, which reduces heart rate and blood pressure
- Propranolol's less selective nature may lead to more bronchospasm in susceptible patients like those with asthma, as noted in guidelines for managing patients with supraventricular tachycardia 1 and unstable angina/non-ST-elevation myocardial infarction 1.
Given the most recent and highest quality evidence, the recommended equivalent dose of propranolol for metoprolol 40 mg BID is 80 mg BID, considering the pharmacokinetic and pharmacodynamic properties of both drugs, as well as potential side effects and interactions 1.
From the Research
Equivalent Dose of Propranolol to Metoprolol
To determine the equivalent dose of propranolol to metoprolol 40 mg twice a day (BID), we need to consider the potency and dose-response relationships of these beta-blockers.
- The study 2 found that 40 mg of propranolol is equivalent to 49 mg of metoprolol.
- Another study 3 reported that 50 mg of metoprolol corresponds to 40 mg of propranolol in reducing exercise-induced tachycardia, indicating a ratio of 4:5 for metoprolol to propranolol.
- Based on these findings, we can estimate the equivalent dose of propranolol to metoprolol 40 mg BID.
Calculation of Equivalent Dose
- Using the ratio from study 3, we can calculate the equivalent dose of propranolol to metoprolol 40 mg as follows: 40 mg metoprolol x (5/4) = 50 mg propranolol.
- However, study 2 provides a more direct comparison, suggesting that 49 mg of metoprolol is equivalent to 40 mg of propranolol.
- Considering these results, the equivalent dose of propranolol to metoprolol 40 mg BID can be estimated as approximately 80-100 mg propranolol per day, assuming a similar dosing frequency.
Key Points
- The equivalent dose of propranolol to metoprolol 40 mg BID is estimated to be around 80-100 mg propranolol per day.
- This estimate is based on the potency and dose-response relationships of these beta-blockers, as reported in studies 2 and 3.
- It is essential to note that individual patient responses may vary, and dose adjustments should be made under medical supervision 4.