The precise mechanism of action of metoprolol tartrate in patients with suspected or definite myocardial infarction is not known. The study thus was able to wshow a benefit from the overall metoprolol tartrate regimen but cannot separate the benefit of very early intravenous treatment from the benefit of later beta-blocker therapy. Nonetheless, because the overall regimen showed a clear beneficial effect on survival without evidence of an early adverse effect on survival, one acceptable dosage regimen is the precise regimen used in the trial. Because the specific benefit of very early treatment remains to be defined however, it is also reasonable to administer the drug orally to patients at a later time as is recommended for certain other beta blockers. In man, absorption of metoprolol tartrate is rapid and complete.
Plasma levels achieved are highly variable after oral administration.
Elimination is mainly by biotransformation in the liver, and the plasma half-life ranges from approximately 3 to 7 hours. The systemic availability and half-life of metoprolol tartrate in patients with renal failure do not differ to a clinically significant degree from those in normal subjects. Consequently, no reduction in dosage is usually needed in patients with chronic renal failure. After repeated oral dosages of 100 mg twice daily, a significant reduction in exercise systolic blood pressure was evident at 12 hours. When the drug was infused over a 10-minute period, in normal volunteers, maximum beta blockade was achieved at approximately 20 minutes.