METOPROLOL TARTRATE

METOPROLOL TARTRATE (me-toe'proe-lole) Apo-Metoprolol , Betaloc , Lopressor, Toprol XL Classifications: beta-adrenergic antagonist; antihypertensive; antianginal; Therapeutic: antihypertensive; antianginal Prototype: Propranolol Pregnancy Category: C

Availability

25 mg, 50 mg, 100 mg tablets; 25 mg, 50 mg, 100 mg, 200 mg sustained release tablets; 1 mg/mL injection

Action

Beta-adrenergic blocking agent with preferential effect on beta₁ receptors located primarily on cardiac muscle. At higher doses, metoprolol also inhibits beta₂ receptors located chiefly on bronchial and vascular musculature. Antihypertensive action may be due to competitive antagonism of catecholamines at cardiac adrenergic neuron sites, drug-induced reduction of sympathetic outflow to the periphery, and to suppression of renin activity.

Therapeutic Effect

Reduces heart rate and cardiac output at rest and during exercise; lowers both supine and standing BP, slows sinus rate and decreases myocardial automaticity. Antianginal effect is like that of propranolol.

Uses

Management of mild to severe hypertension (monotherapy or in combination with a thiazide or vasodilator or both); long-term treatment of angina pectoris and prophylactic management of stable angina pectoris reduce the risk of mortality after an MI.

Unlabeled Uses

CHF.

Contraindications

Cardiogenic shock, sinus bradycardia, heart block greater than first degree, overt cardiac failure, right ventricular failure secondary to pulmonary hypertension. Safety during pregnancy (category C) or in children is not established.

Cautious Use

Impaired liver or kidney function; cardiomegaly, CHF controlled by digitalis and diuretics; AV conduction defects; bronchial asthma and other bronchospastic diseases; history of allergy; thyrotoxicosis; diabetes mellitus; peripheral vascular disease.

Route & Dosage

Hypertension Adult: PO 50–100 mg/d in 1–2 divided doses, may increase weekly up to 100–450 mg/d Geriatric: PO 25 mg/d (range: 25–300 mg/d) Angina Pectoris Adult: PO 100 mg/d in 2 divided doses, may increase weekly up to 100–400 mg/d Myocardial Infarction Adult: IV 5 mg q2min for 3 doses, followed by PO therapy PO 50 mg q6h for 48 h, then 100 mg b.i.d.

Administration

Oral

• Ensure that sustained-release form is not chewed or crushed. It must be swallowed whole.
• Give with food to slightly enhance absorption; however, administration with food not essential. It is important to give with or without food consistently to minimize possible variations in bioavailability.

Intravenous PREPARE: Direct: Give undiluted.   ADMINISTER: Direct: Give at a rate of 5 mg over 60 sec. Note conditions which are contraindications to drug administration.   INCOMPATIBILITIES Y-site: Amphotericin B cholesteryl complex.

• Store at 15°–30° C (59°–86° F). Protect from heat, light, and moisture.

Adverse Effects (≥1%)

Body as a Whole: Hypersensitivity (erythmatous rash, fever, headache, muscle aches, sore throat, laryngospasm, respiratory distress). CNS: Dizziness, fatigue, insomnia, increased dreaming, mental depression. CV: Bradycardia, palpitation, cold extremities, Raynaud's phenomenon, intermittent claudication, angina pectoris, CHF, intensification of AV block, AV dissociation, complete heart block, cardiac arrest. GI: Nausea, heartburn, gastric pain, diarrhea or constipation, flatulence. Hematologic: Eosinophilia, thrombocytopenic and nonthrombocytopenic purpura, agranulocytosis (rare). Skin: Dry skin, pruritus, skin eruptions. Special Senses: Dry mouth and mucous membranes. Metabolic: Hypoglycemia. Respiratory: Bronchospasm (with high doses), shortness of breath.

Diagnostic Test Interference

In common with other beta blockers, metoprolol may cause elevated BUN and serum creatinine levels (patients with severe heart disease), elevated serum transaminase, alkaline phosphatase, lactate dehydrogenase, and serum uric acid.

Interactions

Drug: barbiturates, rifampin may decrease effects of metoprolol; cimetidine, methimazole, propylthiouracil, oral contraceptives may increase effects of metoprolol; additive bradycardia with digoxin; effects of both metoprolol and hydralazine may be increased; indomethacin may attenuate hypotensive response; beta agonists and metoprolol mutually antagonistic; verapamil may increase risk of heart block and bradycardia; increases terbutaline serum levels.

Pharmacokinetics

Absorption: Readily from GI tract; 50% of dose reaches systemic circulation. Onset: 15 min. Peak: 1.5 h; IV form: 20 min. Duration: 13–19 h. Distribution: Crosses blood–brain barrier and placenta; distributed into breast milk. Metabolism: Extensively in liver (CYP2D6). Elimination: In urine. Half-Life: 3–4 h.

Nursing Implications

Assessment & Drug Effects

• Take apical pulse and BP before administering drug. Report to physician significant changes in rate, rhythm, or quality of pulse or variations in BP prior to administration.
• Monitor BP, HR, and ECG carefully during IV administration.
• Expect maximal effect on BP after 1 wk of therapy.
• Take several BP readings close to the end of a 12 h dosing interval to evaluate adequacy of dosage for patients with hypertension, particularly in patients on twice daily doses. Some patients require doses 3 times a day to maintain satisfactory control.
• Observe hypertensive patients with CHF closely for impending heart failure: Dyspnea on exertion, orthopnea, night cough, edema, distended neck veins.
• Lab tests: Obtain baseline and periodic evaluations of blood cell counts, blood glucose, liver and kidney function.
• Monitor I&O, daily weight; auscultate daily for pulmonary rales.
• Withdraw drug if patient presents symptoms of mental depression because it can progress to catatonia. Possible symptoms of depression: disinterest in people, surroundings, food, personal hygiene; withdrawal, apathy, sadness, difficulty in concentrating, insomnia.
• Monitor patients with thyrotoxicosis closely since drug masks signs of hyperthyroidism (see Appendix F). Abrupt withdrawal may precipitate thyroid storm.

Patient & Family Education

• Learn how to take radial pulse before each dose. Report to physician if pulse is slower than base rate (e.g., 60 bpm) or becomes irregular. Consult physician for parameters.
• Reduce insomnia or increased dreaming by avoiding late evening doses.
• Monitor blood glucose (diabetics) for loss of glycemic control. Drug may mask some symptoms of hypoglycemia (e.g., BP and HR changes) and prolong hypoglycemia. Be alert to other possible signs of hypoglycemia not affected by metoprolol and report to physician if present: Sweating, fatigue, hunger, inability to concentrate.
• Protect extremities from cold and do not smoke. Report cold, painful, or tender feet or hands or other symptoms of Raynaud's disease (intermittent pallor, cyanosis or redness, paresthesias). Physician may prescribe a vasodilator.
• Report immediately to physician the onset of problems with vision.
• Learn measures to relieve dry mouth; rinse mouth frequently with water, increase noncalorie liquid intake if inadequate, suck sugarless gum or hard candy.
• Relieve eye dryness by using sterile artificial tears available OTC.
• Do not drive or engage in potentially hazardous activities until response to drug is known.
• Do not alter established dosage regimen; compliance is very important.
• Reduce dosage reduced gradually over a period of 1–2 wk when drug is discontinued. Sudden withdrawal can result in increase in anginal attacks and MI in patients with angina pectoris and thyroid storm in patients with hyperthyroidism.

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Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug