Note: Original Source for Medical Professionals
Hematologic side effects including agranulocytosis, nonthrombocytopenic purpura and thrombocytopenic purpura have been associated with beta-blocking agents in general.

Patients receiving metoprolol should be advised to avoid abrupt discontinuation of the drug, as severe exacerbation of angina and myocardial infarction have occurred. When discontinuing metoprolol, particularly in patients with ischemic heart disease, the dosage should be reduced gradually over a 1 to 2 week period and the patient should be closely monitored. If angina worsens or acute coronary insufficiency develops, metoprolol should be reinstated quickly, at least temporarily, and other appropriate measures for the management of unstable angina should be taken. Patients should be warned against interruption or discontinuation of treatment without consulting the physician. Because coronary artery disease is common and may be unrecognized, it may be prudent not to discontinue metoprolol treatment abruptly even in patients treated only for hypertension.

The beta-adrenergic blockade of metoprolol may mask certain clinical signs (e.g., tachycardia) of hyperthyroidism. Patients suspected of developing thyrotoxicosis should be managed carefully to avoid abrupt withdrawal of beta-blockade, which might precipitate a thyroid storm.

Digitalis glycosides, clonidine, diltiazem and verapamil slow atrioventricular conduction and decrease heart rate. Concomitant use with beta blockers can increase the risk of bradycardia. If clonidine and a beta blocker, such as metoprolol are co administered, the beta-blocker should be discontinued several days before the gradual withdrawal of clonidine because beta-blockers may exacerbate the rebound hypertension that can follow the withdrawal of clonidine. If replacing clonidine by beta-blocker therapy, delay the introduction of beta-blockers for several days after clonidine administration has stopped.

Metabolic side effects have included significant increases in VLDL cholesterol and total serum triglycerides, and significant decreases in HDL cholesterol. A case of hyperkalemia has been reported. At least one case of metoprolol-associated hypoglycemia has been reported. Very rarely, weight gain has also been reported. Metabolic side effects have included weight gain.

Severe and symptomatic hyperkalemia associated with metoprolol has been reported in a 45-year-old male with diabetes, hypertension, and dialysis-dependent diabetic nephropathy. Cellular potassium channels are beta-receptor mediated. The mechanism by which metoprolol induces weight gain is unknown. Some investigators have reported a 4% to 9% reduction in total energy expenditure and a 25% reduction in thermogenic response to food during beta-blocker treatment.

Musculoskeletal side effects have been reported extremely rarely. Cases of a polymyalgia rheumatica-like syndrome and arthralgia have been reported. Very rarely, arthritis has also been reported.

There are approximately five case reports of severe myalgias/arthralgias in patients without a history of arthritis. In one, a 60-year-old male with hypertension developed a microcytic anemia, weight loss, myalgias, anorexia and fatigue within seven years after starting metoprolol and furosemide. The patient's signs and symptoms resolved within two months after discontinuing metoprolol. A review of the literature reveals that the most commonly affected joints are the knees. Associated complaints may include fever and chills.

Nervous system side effects have included general fatigue in 1% to 10%, dizziness in 1% to 10%, headache in 0.3% to 4.0%, insomnia in 2%, nightmares in 1%, mental confusion, short-term memory loss, and somnolence. Anxiety, nervousness, hallucinations, headache, tinnitus, and paresthesias have been associated with extended release preparations of metoprolol in postmarketing use.

Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat. Call your doctor at once if you have any of these serious side effects: slow or uneven heartbeats; feeling light-headed, fainting; feeling short of breath, even with mild exertion; swelling of your ankles or feet; nausea, stomach pain, low fever, loss of appetite, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes); depression; or cold feeling in your hands and feet. Less serious side effects may include: vomiting; decreased sex drive, impotence, or difficulty having an orgasm; sleep problems (insomnia); tired feeling; or anxiety, nervousness. This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Metoprolol is generally well-tolerated. Ninety-four percent of patients from a large study reported "excellent" or "good" tolerability of metoprolol. Approximately 27% of patients experience at least one side effect from long-term studies, but they are usually mild and transient. Side effects may be more likely and more severe in patients who are slow metabolizers of metoprolol. In a review of heart failure trials, beta-blockers (i.e., carvedilol, metoprolol, bisoprolol) were associated with increased risks of hypotension, dizziness, and bradycardia, but not fatigue compared with placebo. In addition, beta-blocker therapy was associated with fewer overall all-cause withdrawals and less heart failure deterioration than placebo.

Cardiovascular side effects reported in 3% of patients have included bradycardia and dyspnea. AV heart block, syncope, chest pain, hypotension, cold extremities, palpitations, peripheral edema, coronary artery spasm, congestive heart failure, and arterial insufficiency (usually of the Raynaud type) have been reported in 1% of patients. Very rarely, gangrene has been reported in patients with severe preexisting peripheral circulatory disorders. Cardiogenic shock has been reported in patients with acute myocardial infarction in postmarketing studies.

Hepatic toxicity is reported in at least one case report.

A 56-year-old female with a history of migraine headaches developed seronegative hepatitis associated with metoprolol. Her signs and symptoms resolved within 48 hours after discontinuing metoprolol, and were reproducible on rechallenge.

Endocrine side effects including slightly decreased T3 concentrations (without changes in T4 concentrations) have been reported among patients with hyperthyroidism.

Note: Original Source for Medical Professionals
Patients receiving metoprolol should be advised to avoid abrupt discontinuation of the drug, as severe exacerbation of angina and myocardial infarction have occurred. When discontinuing metoprolol, particularly in patients with ischemic heart disease, the dosage should be reduced gradually over a 1 to 2 week period and the patient should be closely monitored. If angina worsens or acute coronary insufficiency develops, metoprolol should be reinstated quickly, at least temporarily, and other appropriate measures for the management of unstable angina should be taken. Patients should be warned against interruption or discontinuation of treatment without consulting the physician. Because coronary artery disease is common and may be unrecognized, it may be prudent not to discontinue metoprolol treatment abruptly even in patients treated only for hypertension.

The beta-adrenergic blockade of metoprolol may mask certain clinical signs (e.g., tachycardia) of hyperthyroidism. Patients suspected of developing thyrotoxicosis should be managed carefully to avoid abrupt withdrawal of beta-blockade, which might precipitate a thyroid storm.

Metabolic side effects have included significant increases in VLDL cholesterol and total serum triglycerides, and significant decreases in HDL cholesterol. A case of hyperkalemia has been reported. At least one case of metoprolol-associated hypoglycemia has been reported. Very rarely, weight gain has also been reported. Metabolic side effects have included weight gain.

Severe and symptomatic hyperkalemia associated with metoprolol has been reported in a 45-year-old male with diabetes, hypertension, and dialysis-dependent diabetic nephropathy. Cellular potassium channels are beta-receptor mediated. The mechanism by which metoprolol induces weight gain is unknown. Some investigators have reported a 4% to 9% reduction in total energy expenditure and a 25% reduction in thermogenic response to food during beta-blocker treatment.

Musculoskeletal side effects have been reported extremely rarely. Cases of a polymyalgia rheumatica-like syndrome and arthralgia have been reported. Very rarely, arthritis has also been reported.

There are approximately five case reports of severe myalgias/arthralgias in patients without a history of arthritis. In one, a 60-year-old male with hypertension developed a microcytic anemia, weight loss, myalgias, anorexia and fatigue within seven years after starting metoprolol and furosemide. The patient's signs and symptoms resolved within two months after discontinuing metoprolol. A review of the literature reveals that the most commonly affected joints are the knees. Associated complaints may include fever and chills.

Nervous system side effects have included general fatigue in 1% to 10%, dizziness in 1% to 10%, headache in 0.3% to 4.0%, insomnia in 2%, nightmares in 1%, mental confusion, short-term memory loss, and somnolence. Anxiety, nervousness, hallucinations, headache, tinnitus, and paresthesias have been associated with extended release preparations of metoprolol in postmarketing use.

Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat. Call your doctor at once if you have any of these serious side effects: slow or uneven heartbeats; feeling light-headed, fainting; feeling short of breath, even with mild exertion; swelling of your ankles or feet; nausea, stomach pain, low fever, loss of appetite, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes); depression; or cold feeling in your hands and feet. Less serious side effects may include: vomiting; decreased sex drive, impotence, or difficulty having an orgasm; sleep problems (insomnia); tired feeling; or anxiety, nervousness. This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Metoprolol is generally well-tolerated. Ninety-four percent of patients from a large study reported "excellent" or "good" tolerability of metoprolol. Approximately 27% of patients experience at least one side effect from long-term studies, but they are usually mild and transient. Side effects may be more likely and more severe in patients who are slow metabolizers of metoprolol. In a review of heart failure trials, beta-blockers (i.e., carvedilol, metoprolol, bisoprolol) were associated with increased risks of hypotension, dizziness, and bradycardia, but not fatigue compared with placebo. In addition, beta-blocker therapy was associated with fewer overall all-cause withdrawals and less heart failure deterioration than placebo.

Hepatic toxicity is reported in at least one case report.

A 56-year-old female with a history of migraine headaches developed seronegative hepatitis associated with metoprolol. Her signs and symptoms resolved within 48 hours after discontinuing metoprolol, and were reproducible on rechallenge.

Endocrine side effects including slightly decreased T3 concentrations (without changes in T4 concentrations) have been reported among patients with hyperthyroidism.