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Early intravenous then oral metoprolol in 45852 patients with acute myocardial infarction: randomised placebo-controlled trial - The Lancet - 2005

Brief Summary:

Among patients with acute MI not undergoing PCI, a regimen of IV metoprolol followed by high-dose oral metoprolol succinate does not reduce the composite rate of death, reinfarction, or cardiac arrest, but does increase rates of cardiogenic shock.

Reference:
http://www.ncbi.nlm.nih.gov/pubmed/16271643