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warnings
WARNINGS Myocardial Infarction Cardiac Failure: Sympathetic stimulation is a vital component supporting circulatory function, and beta blockade carries the potential hazard of depressing myocardial contractility and precipitating or exacerbating minimal cardiac failure. During treatment with metoprolol, the hemodynamic status of the patient should be carefully monitored. If heart failure occurs or persists despite appropriate treatment, metoprolol should be discontinued. Bradycardia: Metoprolol produces a decrease in sinus heart rate in most patients; this decrease is greatest among patients with high initial heart rates and least among patients with low initial heart rates. Acute myocardial infarction (particularly inferior infarction) may in itself produce significant lowering of the sinus rate. If the sinus rate decreases to < 40 beats/min, particularly if associated with evidence of lowered cardiac output, atropine (0.25-0.5 mg) should be administered intravenously. If treatment with atropine is not successful, metoprolol should be discontinued, and cautious administration of isoproterenol or installation of a cardiac pacemaker should be considered. AV Block: Metoprolol slows AV conduction and may produce significant first-(P-R interval ≥0.26 sec), second-, or third-degree heart block. Acute myocardial infarction also produces heart block. If heart block occurs, metoprolol should be discontinued and atropine (0.25-0.5 mg) should be administered intravenously. If treatment with atropine is not successful, cautious administration of isoproterenol or installation of a cardiac pacemaker should be considered. Hypotension: If hypotension (systolic blood pressure ≤90 mmHg) occurs, metoprolol should be discontinued, and the hemodynamic status of the patient and the extent of myocardial damage carefully assessed. Invasive monitoring of central venous, pulmonary capillary wedge, and arterial pressures may be required. Appropriate therapy with fluids, positive inotropic agents, balloon counterpulsation, or other treatment modalities should be instituted. If hypotension is associated with sinus bradycardia or AV block, treatment should be directed at reversing these (see above ). Bronchospastic Diseases: PATIENTS WITH BRONCHOSPASTIC DISEASES SHOULD, IN GENERAL, NOT RECEIVE BETA BLOCKERS. Because of its relative beta 1 selectivity, metoprolol may be used with extreme caution in patients with bronchospastic disease. Because it is unknown to what extent beta 2 -stimulating agents may exacerbate myocardial ischemia and the extent of infarction, these agents should not be used prophylactically. If bronchospasm not related to congestive heart failure occurs, metoprolol should be discontinued. A theophylline derivative or a beta 2 agonist may be administered cautiously, depending on the clinical condition of the patient. Both theophylline derivatives and beta 2 agonists may produce serious cardiac arrhythmias.
ADVERSE REACTIONS Myocardial Infarction Central Nervous System: Tiredness has been reported in about 1 of 100 patients. Vertigo, sleep disturbances, hallucinations, headache, dizziness, visual disturbances, confusion, and reduced libido have also been reported, but a drug relationship is not clear. Cardiovascular: In the randomized comparison of metoprolol and placebo described in the CLINICAL PHARMACOLOGY section, the following adverse reactions were reported: Metoprolol Placebo Hypotension 27.4% 23.2% (systolic BP < 90 mmHg) Bradycardia 15.9% 6.7% (heart rate < 40 beats/min) Second- or third-degree heart block 4.7% 4.7% First-degree heart block 5.3% 1.9% (P-R ≥ 0.26 sec) Heart failure 27.5% 29.6% Respiratory: Dyspnea of pulmonary origin has been reported in fewer than 1 of 100 patients. Gastrointestinal: Nausea and abdominal pain have been reported in fewer than 1 of 100 patients. Dermatologic: Rash and worsened psoriasis have been reported, but a drug relationship is not clear. Miscellaneous: Unstable diabetes and claudication have been reported, but a drug relationship is not clear. Potential Adverse Reactions A variety of adverse reactions not listed above have been reported with other beta-adrenergic blocking agents and should be considered potential adverse reactions to metoprolol. Central Nervous System: Reversible mental depression progressing to catatonia; an acute reversible syndrome characterized by disorientation for time and place, short-term memory loss, emotional lability, slightly clouded sensorium, and decreased performance on neuropsychometrics. Cardiovascular: Intensification of AV block (see CONTRAINDICATIONS ). Hematologic: Agranulocytosis, nonthrombocytopenic purpura, thrombocytopenic purpura. Hypersensitive Reactions: Fever combined with aching and sore throat, laryngospasm, and respiratory distress.