Metoprolol Tartrate

Available brands

Indications

ln the management of hypertension and angina pectoris. Cardiac arrhythmias, especially supraventricular tachyarrhythmias. Adjunct to the treatment of hyperthyroidism. Early intervention with Metoprolol in acute myocardial infarction reduces infarct size and the incidence of ventricular fibrillation. Pain relief may also decrease the need for opiate analgesics. Metoprolol has been shown to reduce mortality when administered to patients with acute myocardial infarction.

Pharmacology

Metoprolol is a selective beta1-blocker. Metoprolol reduces or inhibits the agonistic effect on the heart of catecholamines (which are released during physical and mental stress). This means that the usual increase in heart rate, cardiac output, cardiac contractility and blood pressure, produced by the acute increase in catecholamines, is reduced by Metoprolol. Metoprolol interferes less with Insulin release and carbohydrate metabolism than do non-selective beta-blockers. Metoprolol interferes much less with the cardiovascular response to hypoglycaemia than do non-selective beta-blockers.

Dosage & Administration

Film-coated tablet-

Hypertension: Total daily dosage Metoprolol 100-400 mg to be given as a single or twice-daily dose. The starting dose is 100 mg (two Metoprolol-50 tablets) per day. This may be increased by 100 mg per day at weekly intervals. lf full control is not achieved using a single daily dose, a b.i.d. regimen should be initiated. Combination therapy with a diuretic or other antihypertensive agents may also be considered.
Angina: Usually Metoprolol 50 mg (one Metoprolol-50 tablet) to 100 mg (two Metoprolol-50 tablets) twice or three times daily.
Cardiac arrhythmias: Metoprolol 50 mg (one Metoprolol-50 tablet) b.i.d or t.i.d should usually control the condition. It is necessary the dose can be increased up to 300 mg per day in divided doses. Following the treatment of an acute arrhythmia with Metoprolol injection, continuation therapy with Metoprolol tablets should be initiated 4-6 hours later. The initial oral dose should not exceed 50 mg t.i.d.
Hyperthyroidism: Metoprolol 50 mg (one Metoprolol-50 tablet) four times a day. The dose should be reduced as the euthyroid state is achieved.
Myocardial infarction: Orally, therapy should commence 15 minutes after the last injection with 50 mg every 6 hours for 48 hours. Patients who fail to tolerate the full intravenous dose should be given half the suggested oral dose. Maintenance- The usual maintenance dose is 200 mg daily given in divided doses. Elderly’ There are no special dosage requirements in otherwise healthy elderly patients. Significant hepatic dysfunction: A reduction in dosage may be necessary.

Extended-release tablet-

Hypertension: The usual initial dosage is 25 to 100 mg daily in a single dose, whether used alone or added to a diuretic.
Angina Pectoris: The dosage of extended-release Metoprolol Succinate should be individualized. The usual initial dosage is 100 mg daily, in a single dose.
Heart Failure: The recommended starting dose of sustained-release Metoprolol Succinate is 25 mg once daily for two weeks in patients with NYHA class II heart failure and 12.5 mg once daily in patients with more severe heart failure. The dosage may be increased at weekly (or longer) intervals until optimum blood pressure reduction is achieved. If treatment is to be discontinued, the dosage should be reduced gradually over a period of 1-2 weeks.

IV Injection-

Arrhythmias: By intravenous injection, up to 5 mg at a rate of 1-2 mg/minute, repeated after 5 minutes if necessary, total dose 10-15 mg.
In surgery: By slow intravenous injection 2-4 mg at induction or to control arrhythmias developing during anaesthesia; 2 mg doses may be repeated to a maximum of 10 mg.
Myocardial Infarction: Early intervention within 12 hours of infarction, by intravenous injection 5 mg every 2 minutes to a maximum of 15 mg, followed after 15 minutes by 50 mg by mouth every 6 hours for 48 hours; maintenance 200 mg daily in divided doses.

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Interaction

Catecholamine‐depleting drugs (e.g. Reserpine, Monoamine Oxidase (MAO) inhibitors) may have an additive effect when given with beta‐blocking agents. Drugs that inhibit CYP2D6 such as quinidine, fluoxetine, paroxetine and propafenone are likely to increase Metoprolol concentration. These increases in plasma concentration would decrease the cardioselectivity of Metoprolol. Concomitant use of digitalis glycosides and beta‐blockers can increase the risk of bradycardia. Beta‐blockers may exacerbate the rebound hypertension which can follow the withdrawal of clonidine.

Contraindications

AV block, Uncontrolled heart failure, severe bradycardia, sick-sinus syndrome, cardiogenic shock and severe peripheral arterial disease. Known hypersensitivity to Metoprolol or other B-blockers. Metoprolol is also contra-indicated when myocardial infarction is complicated by significant bradycardia, first-degree heart block, systolic hypotension (<100mmHg) and/or severe heart failure.

Side Effects

Tiredness, dizziness, depression, diarrhea, itching or rash, shortness of breath, slow heart rate, mental confusion, headache, somnolence, nightmares, insomnia, dyspnea, Nausea, dry mouth, gastric pain, constipation, flatulence, digestive tract disorders, heartburn, pruritus, musculoskeletal pain, blurred vision, decreased libido, and tinnitus have also been reported, intensification of AV block.

Pregnancy & Lactation

Pregnancy Category C. There are no adequate and well‐controlled studies in pregnant women. This drug should be used during pregnancy only if clearly needed. Metoprolol is excreted in breast milk in very small quantities. Caution should be exercised when Metoprolol is administered to a nursing woman.

Precautions & Warnings

Bronchospastic Diseases: Because of its relative beta 1 ‐selectivity, however, Metoprolol may be used with caution in patients with bronchospastic disease who do not respond to, or cannot tolerate other antihypertensive treatment.

Major Surgery: The necessity or desirability of withdrawing beta‐blocking therapy prior to major surgery is controversial; the impaired ability of the heart to respond to reflex adrenergic stimuli may augment the risks of general anesthesia and surgical procedures.

Diabetes and Hypoglycemia: Beta‐blockers may mask tachycardia occurring with hypoglycemia, but other manifestations such as dizziness and sweating may not be significantly affected. Peripheral Vascular Disease: Beta‐blockers can precipitate or aggravate symptoms of arterial insufficiency in patients with peripheral vascular disease. Calcium Channel Blockers: Because of significant inotropic and chronotropic effects in patients, caution should be exercised in patients treated with these agents concomitantly.

Use in Special Populations

Hepatic impaired patient: Metoprolol should be used with caution in patients with impaired hepatic function.

Pediatric Use: No clinically relevant differences in the adverse event profile were observed for pediatric patients aged 6 to 16 years as compared with adult patients. Safety and effectiveness of Metoprolol have not been established in patients <6 years of age.

Geriatric Use: There were no notable differences in efficacy or the rate of adverse events between older and younger patients.

Overdose Effects

Poisoning due to an overdose of metoprolol may lead to severe hypotension, sinus bradycardia, atrioventricular block, heart failure, cardiogenic shock, cardiac arrest, bronchospasm, impairment of consciousness, coma, nausea, vomiting, cyanosis, hypoglycaemia and, occasionally, hyperkalaemia. The first manifestations usually appear 20 minutes to 2 hours after drug ingestion. Treatment: Treatment should include close monitoring of cardiovascular, respiratory and renal function, and blood glucose and electrolytes. Further absorption may be prevented by induction of vomiting, gastric lavage or administration of activated-charcoal if ingestion is recent. Cardiovascular complications should be treated symptomatically, which may require the use of sympathomimetic agents (e.g. noradrenaline, metaramionl), atropine or inotropic agents (e.g. dopamine, dobutamine). Temporary pacing may be required for AV block. Glucagon can reverse the effects of excessive B-blockade, given in a dose of 1-10 mg intravenously. Intravenous B2-stimulants e.g. terbutaline may be required to relieve bronchospasm. Metoprolol cannot be effectively removed by haemodialysis.