metoprolol succinate

Action

Blocks stimulation of beta₁ (myocardial) adrenergic receptors, usually without affecting beta₂ (pulmonary, vascular, uterine) adrenergic receptor sites

Availability

Injection (tartrate): 1 mg/ml

Tablets: 50 mg, 100 mg

Tablets (extended-release, succinate): 25 mg, 50 mg, 100 mg, 200 mg

Indications and dosages

➣ Hypertension

Adults: 50 to 100 mg P.O. daily as a single dose or in two divided doses (conventional tablets) or once daily (extended-release tablets). May be increased q 7 days as needed, up to 450 mg/day (tartrate) or 400 mg (succinate extended-release).

➣ Angina pectoris

Adults: 100 mg P.O. daily as a single dose or in two divided doses (conventional tablets) or once daily (extended-release tablets). May be increased q 7 days as needed, up to 400 mg.

➣ MI

Adults: Three bolus injections of 5 mg I.V. given at 2-minute intervals. If patient tolerates I.V. dose, give 50 mg P.O. 15 minutes after last I.V. dose, and continue P.O. doses q 6 hours for 48 hours. For maintenance, 100 mg P.O. b.i.d. If patient doesn't tolerate full I.V. dose, give 25 to 50 mg P.O. (depending on degree of intolerance), starting 15 minutes after last I.V. dose or when clinical condition allows; discontinue drug if patient shows severe intolerance. As late treatment, 100 mg P.O. b.i.d. when clinical condition allows, continued for at least 3 months.

➣ Symptomatic heart failure

Adults: 25 mg P.O. daily (extended-release tablets) in patients with NYHA Class II heart failure. Dosage may be doubled q 2 weeks, up to 200 mg/day or until highest tolerated dosage is reached. For more severe heart failure, start with 12.5 mg P.O. daily.

Off-label uses

• Ventricular arrhythmias, tachycardia

• Tremors

• Anxiety

Contraindications

• Sinus bradycardia, heart block greater than first degree, cardiogenic shock, overt cardiac failure (with Lopressor used for hypertension or angina)

• Heart rate below 45 beats/minute, second- or third-degree heart block, significant first-degree heart block; systolic pressure below 100 mm Hg; or moderate-to-severe cardiac failure (when Lopressor is used for MI)

• Hypersensitivity to drug or its components, severe bradycardia, heart block greater than first degree, cardiogenic shock, decompensated cardiac failure, sick sinus syndrome (unless permanent pacemaker is in place) (with Toprol-XL)

Precautions

Use cautiously in:

• renal or hepatic impairment, pulmonary disease, diabetes mellitus, thyrotoxicosis

• MAO inhibitor use within past 14 days

• pregnant or breastfeeding patients

• children (safety not established).

Administration

• Give metoprolol tartrate with or immediately after meals, because food enhances its absorption.

• Know that succinate extended-release tablets are scored and can be divided. However, tablet or half-tablet should be swallowed whole and not crushed or chewed.

• For I.V. administration, give each dose undiluted by direct injection over at least 1 minute.

Adverse reactions

CNS: fatigue, weakness, anxiety, depression, dizziness, drowsiness, insomnia, memory loss, mental status changes, nervousness, nightmares

CV: orthostatic hypotension, peripheral vasoconstriction, bradycardia, heart failure, pulmonary edema

EENT: blurred vision, stuffy nose

GI: nausea, vomiting, constipation, diarrhea, flatulence, gastric pain, heartburn, dry mouth

GU: urinary frequency, erectile dysfunction, decreased libido

Hepatic: hepatitis

Metabolic: hyperglycemia, hypoglycemia

Respiratory: wheezing, bronchospasm

Musculoskeletal: back pain, joint pain

Skin: rash

Other: drug-induced lupus syndrome

Interactions

Drug-drug. Amphetamines, ephedrine, epinephrine, norepinephrine, phenylephrine, pseudoephedrine: unopposed alpha-adrenergic stimulation (excessive hypertension, bradycardia)

Antihypertensives, nitrates: additive hypotension

Digoxin: additive bradycardia

Dobutamine, dopamine: reduced cardiovascular benefits of these drugs

General anesthestics, phenytoin (I.V.), verapamil: additive myocardial depression

Insulin, oral hypoglycemics: altered efficacy of these drugs

MAO inhibitors: hypertension

Drug-diagnostic tests. Alanine aminotransferase, alkaline phosphatase, aspartate aminotransferase, blood urea nitrogen, glucose, lactate dehydrogenase, lipoproteins, potassium, triglycerides, uric acid: increased levels

Drug-food. Any food: enhanced drug absorption

Drug-behaviors. Acute alcohol ingestion: additive hypotension

Cocaine use: unopposed alpha-adrenergic stimulation (excessive hypertension, bradycardia)

Patient monitoring

• Measure blood pressure closely when starting therapy and titrating dosage. Once patient stabilizes, measure blood pressure every 3 to 6 months.

• Monitor blood pressure and pulse before I.V. administration. If patient is hypotensive or has bradycardia, consult prescriber before giving dose.

• Watch for orthostatic hypotension in at-risk patients, particularly the elderly.

• Assess glucose levels in diabetic patient. Be aware that drug may mask signs and symptoms of hypoglycemia.

• Monitor for signs and symptoms of hyperthyroidism. Know that drug may mask these. Reduce dosage gradually in hyperthyroid patients.

See When discontinuing drug, reduce dosage gradually over 1 to 2 weeks.

Patient teaching

• Advise patient to take with or immediately after meals.

• Tell patient that extended-release tablets are scored and can be divided, but that he should swallow tablets or half-tablets whole and not crush or chew them.

See Advise patient with heart failure to report signs or symptoms of worsening condition, including weight gain and increasing shortness of breath.

• Caution patient to avoid driving and other hazardous activities until drug effects are known.

• Instruct patient to notify health care providers (including dentists) that he is taking drug before having surgery.

• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs, tests, foods, and behaviors mentioned above.