Side Effects of Lopressor (metoprolol)

Lopressor (metoprolol) is a beta-blocker (beta-adrenergic blocking agent) used to treat high blood pressure (hypertension), heart pain (angina pectoris) related to coronary artery disease, congestive heart failure, hyperthyroidism, certain types of tremors, certain types of abnormally rapid heart rates (tachycardias), and some neurologic conditions.

Lopressor is used off-label (not an approved use by the Food and Drug Administration, or FDA) to prevent migraine headaches.

Common side effects of Lopressor include

• abdominal cramps,
• diarrhea,
• constipation,
• fatigue,
• insomnia,
• indigestion,
• nausea,
• depression,
• dreaming,
• memory loss,
• fever,
• impotence,
• lightheadedness,
• low blood pressure,
• decreased exercise tolerance,
• increased triglycerides,
• bronchospasm,
• cold extremities,
• sore throat, and
• shortness of breath or wheezing.

Serious side effects of Lopressor include

• slow heart rate,
• Raynaud's phenomenon,
• hepatitis, and
• increased insulin resistance.

Lopressor can aggravate breathing difficulties in patients with asthma, chronic bronchitis, or emphysema.

Drug interactions of Lopressor include calcium channel blockers and digoxin, which can lower blood pressure and heart rate to dangerous levels when administered together with Lopressor.

• Lopressor can mask the early warning symptoms of low blood sugar (hypoglycemia) and should be used with caution in patients receiving treatment for diabetes.
• Fluoxetine can increase blood levels of Lopressor by reducing breakdown of Lopressor, and increase the side effects from Lopressor.

Safe use of Lopressor during pregnancy has not been established.

Small quantities of Lopressor are excreted in breast milk and may potentially cause adverse effects in the infant. Consult your doctor before breastfeeding. 

Metoprolol is generally well tolerated. Side effects include

• abdominal cramps,
• diarrhea,
• constipation,
• fatigue,
• insomnia,
• indigestion,
• nausea,
• depression,
• dreaming,
• memory loss,
• fever,
• impotence,
• lightheadedness,
• low blood pressure,
• decreased exercise tolerance,
• increased triglycerides,
• bronchospasm,
• cold extremities,
• sore throat, and
• shortness of breath or wheezing.

Possible serious adverse effects include

• slow heart rate,
• Raynaud's phenomenon,
• hepatitis, and
• increased insulin resistance.

Metoprolol can aggravate breathing difficulties in patients with asthma, chronic bronchitis, or emphysema.

WARNING:

• In patients with existing slow heart rates (bradycardias) and heart blocks (defects in the electrical conduction of the heart), metoprolol can cause dangerously slow heart rates, and even shock. Metoprolol reduces the force of heart muscle contraction and can aggravate symptoms of heart failure. In patients with coronary artery disease, abruptly stopping metoprolol can suddenly worsen angina, and occasionally precipitate heart attacks. If it is necessary to discontinue metoprolol, its dosage should be reduced gradually over several weeks.
• Initiation of high-dose extended release metoprolol in patients undergoing non-cardiac surgery is associated with bradycardia (slow heart rate), hypotension, stroke, and death. However, long-term therapy with metoprolol should not be routinely withdrawn prior to major surgery. Impaired ability of the heart to respond to reflex adrenergic stimuli may increase the risks of general anesthesia and surgery.

Hypertension And Angina

These adverse reactions were reported for treatment with oral Lopressor. Most adverse effects have been mild and transient.

Central Nervous System

Tiredness and dizziness have occurred in about 10 of 100 patients. Depression has been reported in about 5 of 100 patients. Mental confusion and short-term memory loss have been reported. Headache, nightmares, and insomnia have also been reported.

Cardiovascular

Shortness of breath and bradycardia have occurred in approximately 3 of 100 patients. Cold extremities; arterial insufficiency, usually of the Raynaud type; palpitations; congestive heart failure; peripheral edema; and hypotension have been reported in about 1 of 100 patients. Gangrene in patients with pre-existing severe peripheral circulatory disorders has also been reported very rarely.

Respiratory

Wheezing (bronchospasm) and dyspnea have been reported in about 1 of 100 patients. Rhinitis has also been reported.

Gastrointestinal

Diarrhea has occurred in about 5 of 100 patients. Nausea, dry mouth, gastric pain, constipation, flatulence, and heartburn have been reported in about 1 of 100 patients. Vomiting was a common occurrence. Postmarketing experience reveals very rare reports of hepatitis, jaundice and nonspecific hepatic dysfunction. Isolated cases of transaminase, alkaline phosphatase, and lactic dehydrogenase elevations have also been reported.

Hypersensitive Reactions

Pruritus or rash have occurred in about 5 of 100 patients. Very rarely, photosensitivity and worsening of psoriasis has been reported.

Miscellaneous

Peyronie's disease has been reported in fewer than 1 of 100,000 patients. Musculoskeletal pain, blurred vision, and tinnitus have also been reported.

There have been rare reports of reversible alopecia, agranulocytosis, and dry eyes. Discontinuation of the drug should be considered if any such reaction is not otherwise explicable. There have been very rare reports of weight gain, arthritis, and retroperitoneal fibrosis (relationship to Lopressor has not been definitely established).

The oculomucocutaneous syndrome associated with the beta blocker practolol has not been reported with Lopressor.

Myocardial Infarction

These adverse reactions were reported from treatment regimens where intravenous Lopressor was administered, when tolerated.

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 Lopressor and placebo described in the prescribing information, the following adverse reactions were reported:

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 Lopressor.

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.

Hematologic: Agranulocytosis, nonthrombocytopenic purpura, and thrombocytopenic purpura.

Hypersensitive Reactions: Fever combined with aching and sore throat, laryngospasm, and respiratory distress.

Postmarketing Experience

The following adverse reactions have been reported during postapproval use of Lopressor: confusional state, an increase in blood triglycerides and a decrease in High Density Lipoprotein (HDL). Because these reports are from a population of uncertain size and are subject to confounding factors, it is not possible to reliably estimate their frequency.

Catecholamine-Depleting Drugs

Catecholamine-depleting drugs (e.g., reserpine) may have an additive effect when given with beta-blocking agents or monoamine oxidase (MAO) inhibitors. Observe patients treated with Lopressor plus a catecholamine depletor for evidence of hypotension or marked bradycardia, which may produce vertigo, syncope, or postural hypotension.

In addition, possibly significant hypertension may theoretically occur up to 14 days following discontinuation of the concomitant administration with an irreversible MAO inhibitor.

Digitalis Glycosides And Beta Blockers

Both digitalis glycosides and beta blockers slow atrioventricular conduction and decrease heart rate. Concomitant use can increase the risk of bradycardia. Monitor heart rate and PR interval.

Calcium Channel Blockers

Concomitant administration of a beta-adrenergic antagonist with a calcium channel blocker may produce an additive reduction in myocardial contractility because of negative chronotropic and inotropic effects.

General Anesthetics

Some inhalation anesthetics may enhance the cardiodepressant effect of beta blockers.

CYP2D6 Inhibitors

Potent inhibitors of the CYP2D6 enzyme may increase the plasma concentration of Lopressor which would mimic the pharmacokinetics of CYP2D6 poor metabolizer. Increase in plasma concentrations of metoprolol would decrease the cardioselectivity of metoprolol.

Known clinically significant potent inhibitors of CYP2D6 are antidepressants such as fluvoxamine, fluoxetine, paroxetine, sertraline,bupropion, clomipramine, and desipramine; antipsychotics such as chlorpromazine, fluphenazine, haloperidol, and thioridazine; antiarrhythmics such as quinidine or propafenone; antiretrovirals such as ritonavir; antihistamines such as diphenhydramine; antimalarials such as hydroxychloroquine or quinidine; antifungals such as terbinafine.

Hydralazine

Concomitant administration of hydralazine may inhibit presystemic metabolism of metoprolol leading to increased concentrations of metoprolol.

Alpha-Adrenergic Agents

Antihypertensive effect of alpha-adrenergic blockers such as guanethidine, betanidine, reserpine, alpha-methyldopa or clonidine may be potentiated by beta-blockers including Lopressor. Beta- adrenergic blockers may also potentiate the postural hypotensive effect of the first dose of prazosin, probably by preventing reflex tachycardia.

On the contrary, beta adrenergic blockers may also potentiate the hypertensive response to withdrawal of clonidine in patients receiving concomitant clonidine and beta-adrenergic blocker. If a patient is treated with clonidine and Lopressor concurrently, and clonidine treatment is to be discontinued, stop Lopressor several days before clonidine is withdrawn. Rebound hypertension that can follow withdrawal of clonidine may be increased in patients receiving concurrent beta-blocker treatment.

Ergot Alkaloid

Concomitant administration with beta-blockers may enhance the vasoconstrictive action of ergot alkaloids.

Dipyridamole

In general, administration of a beta-blocker should be withheld before dipyridamole testing, with careful monitoring of heart rate following the dipyridamole injection.