Metoprolol and Labetalol.

Q: What is the equivalency ratio of Metoprolol and Labetalol?

Answer: 1:2 

Metoprolol and Labetalol are the two most widely used B-blockers in ICUs. 50 mg of Metoprolol is equivalent to 100 mg of Labetalol.

Metoprolol is a selective beta-blocker. Labetalol is an alpha-1 and non-selective b1 blocker. Due to its alpha-1 blocking effect, it reduces the SVR without reducing total peripheral blood flow.

Beta-blockers are lipophilic and so have a tendency to diffuse into adipose tissues. This may lead to restricted tissue distribution in obese patients. Obese patients may require higher doses. 

Labetalol is unique in the sense that its oral and intravenous (IV) forms have different alpha and beta effects. the ratio of the beta-alpha blocker effect is

• 3:1 after oral 
• 7:1 after IV 

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References:

1. Frishman WH, Michelson EL, Johnson BF, Poland MP. Multiclinic comparison of labetalol to metoprolol in treatment of mild to moderate systemic hypertension. Am J Med. 1983 Oct 17;75(4A):54-67. doi: 10.1016/0002-9343(83)90137-7. PMID: 6356900.

2. https://www.drugs.com/compare/labetalol-vs-metoprolol (last accessed January 10, 2024)

3. MacCarthy EP, Bloomfield SS. Labetalol: a review of its pharmacology, pharmacokinetics, clinical uses and adverse effects. Pharmacotherapy. 1983 Jul-Aug;3(4):193-219. doi: 10.1002/j.1875-9114.1983.tb03252.x. PMID: 6310529.