Pharmacy Author: Omudhome Ogbru, PharmD
Medical and Pharmacy Editor: Jay W. Marks, MD

GENERIC NAME: metoprolol

BRAND NAMES: Lopressor, Toprol XL

DRUG CLASS AND MECHANISM: Metoprolol is a beta-adrenergic blocking agent that is used for treating high blood pressure, heart pain, abnormal rhythms of the heart, and some neurologic conditions. Examples of beta-adrenergic blockers include propanolol (Inderal), atenolol (Tenormin), and timolol (Blocadren). Metoprolol blocks the action of the sympathetic nervous system, a portion of the involuntary nervous system, by blocking beta receptors on sympathetic nerves. Since the sympathetic nervous system is responsible for increasing the rate with which the heart beats, by blocking the action of these nerves metoprolol reduces the heart rate and is useful in treating abnormally rapid heart rhythms.

Metoprolol also reduces the force of contraction of heart muscle and thereby lowers blood pressure. By reducing the heart rate and the force of muscle contraction, metoprolol reduces the need for oxygen by heart muscle. Since heart pain (angina pectoris) occurs when oxygen demand of the heart muscle exceeds the supply of oxygen, metoprolol, by reducing the demand for oxygen, is helpful in treating heart pain. The FDA approved metoprolol in August 1978.

PRESCRIPTION: Yes

GENERIC AVAILABLE: Yes

PREPARATIONS: Tablets: 25, 50, and 100 mg. Tablets (extended release): 25, 50, 100, and 200 mg. Injection: 1 mg/ml

STORAGE: Tablets should be stored between 15-30°C (59-86°F). They should be protected from moisture and dispensed in tight, light-resistant container.

PRESCRIBED FOR: Metoprolol is prescribed for patients with high blood pressure (hypertension). It is also used to treat chest pain (angina pectoris) related to coronary artery disease. Metoprolol is also useful in slowing and regulating certain types of abnormally rapid heart rates (tachycardias). Other uses for metoprolol include the prevention of migraine headache and the treatment of certain types of tremors (familial or hereditary essential tremors).

DOSING: Metoprolol should be taken before meals or at bedtime. The dose for treating hypertension is 100-450 mg daily in single or divided doses. Angina is treated with 100-400 mg daily in two divided doses. Acute myocardial infarction is treated with three 5 mg injections administered 2 minutes apart followed by treatment with 50 mg oral metoprolol every 6 hours for 48 hours. After 48 hours, patients should receive 100 mg orally twice daily for at least 3 months.

DRUG INTERACTIONS: Calcium channel blockers and digoxin (Lanoxin) can lower of blood pressure and heart rate to dangerous levels when administered together with metoprolol.

Metoprolol can mask the early warning symptoms of low blood sugar (hypoglycemia) and should be used with caution in patients receiving treatment for diabetes.

PREGNANCY: Safe use of metoprolol during pregnancy has not been established.

NURSING MOTHERS: Small quantities of metoprolol are excreted in breast milk and may potentially cause adverse effects in the infant.

SIDE EFFECTS: Metoprolol is generally well tolerated. Side effects include abdominal cramps, diarrhea, constipation, fatigue, insomnia, nausea, depression, dreaming, memory loss, fever, impotence, lightheadedness, slow heart rate, low blood pressure, cold extremities, sore throat, and shortness of breath or wheezing. Metoprolol can aggravate breathing difficulties in patients with asthma, chronic bronchitis, or emphysema.

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.

From the Doctors at MedicineNet.com

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