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Clinical Pharmacology
CLINICAL PHARMACOLOGY
General Metoprolol is a beta 1 -selective (cardioselective) adrenergic receptor blocking agent. Text Continues Below
This preferential effect is not absolute, however, and at higher plasma concentrations, metoprolol also inhibits beta 2 -adrenoreceptors, chiefly located in the bronchial and vascular musculature. Metoprolol has no intrinsic sympathomimetic activity, and membrane-stabilizing activity is detectable only at plasma concentrations much greater than required for beta-blockade. Animal and human experiments indicate that meto-prolol slows the sinus rate and decreases AV nodal conduction. Clinical pharmacology studies have confirmed the beta-blocking activity of metoprolol in man, as shown by (1) reduction in heart rate and cardiac output at rest and upon exercise, (2) reduction of systolic blood pressure upon exercise, (3) inhibition of isoproterenol-induced tachycardia, and (4) reduction of reflex orthostatic tachycardia. The relative beta 1 -selectivity of metoprolol has been confirmed by the following: (1) In normal subjects, metoprolol is unable to reverse the beta 2 -mediated vasodilating effects of epinephrine. This contrasts with the effect of nonselective beta-blockers, which completely reverse the vasodilating effects of epinephrine. (2) In asthmatic patients, metoprolol reduces FEV 1 and FVC significantly less than a nonselective beta-blocker, propranolol, at equivalent beta 1 -receptor blocking doses. In five controlled studies in normal healthy subjects, the same daily doses of TOPROL-XL and immediate release metoprolol were compared in terms of the extent and duration of beta 1 -blockade produced. Both formulations were given in a dose range equivalent to 100Ð 400 mg of immediate release metoprolol per day. In these studies, TOPROL-XL was administered once a day and immediate release metoprolol was administered once to four times a day. A sixth controlled study compared the beta 1 -blocking effects of a 50 mg daily dose of the two formulations. In each study, beta 1 -blockade was expressed as the percent change from baseline in exercise heart rate following standardized submaximal exercise tolerance tests at steady state. Page: 1 | 2 | 3 | 4 | 5 | Next >>
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