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Cardiac Failure: Sympathetic stimulation is a vital component supporting circulatory function in congestive heart failure, and beta blockade carries the potential hazard of further depressing myocardial contractility and precipitating or exacerbating minimal cardiac failure. Cautiously administer metoprolol in hypertensive and angina patients who have congestive heart failure controlled by digitalis and diuretics. Both digitalis and metoprolol slow AV conduction. Carefully monitor the hemodynamic status of the patient during metoprolol treatment. Discontinue metoprolol if heart failure occurs or persists despite appropriate treatment.
Bronchospastic Diseases: IN GENERAL, PATIENTS WITH BRONCHOSPASTIC DISEASES SHOULD NOT RECEIVE BETA-BLOCKERS, INCLUDING METOPROLOL. Because of its relative beta1 selectivity, however, metoprolol may be used with caution in patients with bronchospastic disease who do not respond to, or cannot tolerate, other antihypertensive treatment. Since beta1 selectivity is not absolute, coadminister a beta2-stimulating agent, and use the lowest possible metoprolol dose. In these cases it would be prudent initially to give metoprolol in smaller doses thrice a day, instead of larger doses twice a day, to avoid higher plasma levels associated with longer dosing intervals.
Because it is not known to what extent beta2-stimulating agents may exacerbate myocardial ischemia and the extent of infarction, these agents should not be used prophylactically. Discontinue metoprolol if bronchospasm not related to congestive heart failure occurs. Administer a theophylline derivative or a beta2-agonist cautiously, depending on the clinical condition of the patient. Both theophylline derivatives and beta2-agonists may produce serious cardiac arrhythmias.
Hypertension and Angina: In Patients without a History of Cardiac Failure: Cardiac failure may result from prolonged depression of myocardium with beta-blockers over a period of time. Fully digitalize and/or give patient a diuretic at the first sign or symptom of impending cardiac failure (e.g., weight gain, increasing shortness of breath). If cardiac failure continues, discontinue metoprolol, gradually if possible.
Major Surgery: The necessity or desirability of withdrawing beta-blockers, including metoprolol, prior to major surgery is controversial. The impaired ability of the heart to respond to reflex adrenergic stimuli may increase the risks of general anesthesia and surgical procedures.
Like other beta-blockers, metoprolol is a competitive inhibitor of beta-receptor agonists, and its effects can be reversed by administration of such agents (e.g., dobutamine or isoproterenol). However, such patients may be subject to protracted severe hypotension. Difficulty in restarting and maintaining the heartbeat has also been observed with beta-blockers.
Diabetes and Hypoglycemia: Use with caution in patients with diabetes mellitus, particularly those who are receiving insulin or oral hypoglycemic agents. Diabetic patients should be warned that beta-blockers, including metoprolol, may mask the tachycardia occurring with hypoglycemia; however, other manifestations of hypoglycemia such as dizziness and sweating may not be significantly affected.
Pheochromocytoma: Metoprolol is contraindicated in patients known to have, or suspected of having, pheochromocytoma. Metoprolol should always be given in combination with an alpha-blocker, and only after the alpha-blocker has been initiated. Administration of beta-blockers alone in the setting of pheochromocytoma has been associated with a paradoxical increase in blood pressure due to the attenuation of beta-mediated vasodilatation in skeletal muscle.
Thyrotoxicosis: Beta-adrenergic blockade may mask certain clinical signs (e.g., tachycardia) of hyperthyroidism. Carefully manage patients suspected of developing thyrotoxicosis to avoid abrupt withdrawal of beta blockade, which might precipitate a thyroid storm.
Myocardial Infarction: Bradycardia: Metoprolol decreases 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, administer atropine 0.25 to 0.5 mg intravenously. Discontinue metoprolol if treatment with atropine is not successful, and consider cautious administration of isoproterenol or installation of a cardiac pacemaker.
AV Block: Metoprolol slows AV conduction and may produce significant first- (P-R interval ≥0.26 sec), second-, or third-degree heart block. Similarly, acute myocardial infarction produces heart block.
Discontinue metoprolol and administer atropine 0.25 to 0.5 mg intravenously if heart block occurs. Consider cautious administration of isoproterenol or installation of a cardiac pacemaker if treatment with atropine is not successful.
Hypotension: Discontinue metoprolol if hypotension (systolic blood pressure ≤90 mmHg) occurs and carefully assess the hemodynamic status of the patient and the extent of myocardial damage. Invasive monitoring of central venous, pulmonary capillary wedge, and arterial pressures may be required. Institute appropriate therapy with fluids, positive inotropic agents, balloon counter pulsation, or other treatment modalities. If hypotension is associated with sinus bradycardia or AV block, treatment should be directed at reversing these.
General: Use with caution in patients with impaired hepatic failure.
Patients should be advised (1) to avoid operating machinery or engaging in other tasks requiring alertness until the patient's response to metoprolol therapy has been determined, (2) to contact the physician if any difficulty in breathing occurs, and (3) to inform the physician/dentist before any type of surgery that he or she is taking metoprolol.
While taking beta-blockers, patients with a history of severe anaphylactic reaction to a variety of allergens may be more reactive to repeated challenge, either accidental, diagnostic, or therapeutic. Such patients may be unresponsive to the usual doses of epinephrine used to treat allergic reaction.
The full oculomucocutaneous syndrome has not been observed with metoprolol; however, part of this syndrome (dry eyes either alone or, occasionally, with skin rashes) has occurred. In most cases, symptoms cleared upon discontinuation of metoprolol. Carefully observe patients for potential ocular effects. If such effects occur, metoprolol should be discontinued.
Use in Children: The safety and efficacy in children have not been established.
Use in the Elderly: There were no age-related differences in safety and efficacy.
