Metoprolol: Uses and Mechanism

• Metoprolol is a beta-1 selective adrenergic blocking agent

Indications

• Hypertension
• Angina pectoris
• Heart failure
• Atrial fibrillation/supraventricular tachycardia
• Acute myocardial infarction (AMI)

Mechanism of Action

• Selectively blocks beta-1 adrenergic receptors in the heart and blood vessels
• Reduces heart rate, contractility, and blood pressure
• Decreases myocardial oxygen demand
• Slows AV nodal conduction

Pharmacokinetics

• Administered orally or intravenously
• Rapidly absorbed
• Undergoes first-pass metabolism in the liver
• Bioavailability is approximately 50%
• Half-life is 3 to 7 hours
• Primarily metabolized by CYP2D6
• Excreted in urine

Dosage and Administration

• Hypertension: 50-100 mg orally twice daily
• Angina: 50-100 mg orally two or three times daily
• Heart failure: Initially 12.5-25 mg orally once daily, gradually increasing to a target dose of 200 mg daily
• Atrial fibrillation: 50 mg orally twice daily
• Acute MI: 5 mg IV bolus repeated every 2-5 minutes for a total of 15 mg, followed by 50 mg orally every 6 hours for 48 hours, then 100 mg orally twice daily

Contraindications

• Severe bradycardia
• Heart block greater than first degree
• Cardiogenic shock
• Decompensated heart failure
• Sick sinus syndrome
• Severe peripheral arterial disease
• Hypersensitivity to metoprolol or other beta-blockers

Warnings and Precautions

• Abrupt cessation of therapy may exacerbate angina or cause myocardial infarction.
• Use with caution in patients with bronchospastic diseases (e.g., asthma, COPD) due to potential for beta-2 blockade
• May mask symptoms of hypoglycemia
• May potentiate the effects of other antihypertensive agents
• Use with caution in patients with peripheral vascular disease
• May worsen heart failure in some patients
• Monitor heart rate and blood pressure regularly

Adverse Reactions

• Common: Bradycardia, hypotension, fatigue, dizziness, depression
• Less common: Heart failure, AV block, bronchospasm, nausea, diarrhea, constipation, rash
• Rare: Thrombocytopenia, elevated liver enzymes, Raynaud's phenomenon

Drug Interactions

• Other antihypertensive agents: May cause additive hypotensive effects
• Antiarrhythmic drugs (e.g., amiodarone): May increase risk of bradycardia and AV block
• Digoxin: May increase risk of bradycardia and AV block
• Calcium channel blockers (e.g., verapamil, diltiazem): May increase risk of bradycardia and AV block
• CYP2D6 inhibitors (e.g., fluoxetine, paroxetine): May increase metoprolol levels
• NSAIDs: May reduce the antihypertensive effect of metoprolol
• Insulin and oral hypoglycemic agents: May mask symptoms of hypoglycemia and require dosage adjustments

Special Populations

• Pregnancy: Metoprolol may cross the placenta and cause fetal bradycardia, hypoglycemia, and respiratory depression; use with caution
• Breastfeeding: Metoprolol is excreted in breast milk; monitor infant for adverse effects
• Elderly: May be more sensitive to the effects of metoprolol; use lower doses
• Renal impairment: No dosage adjustment is usually required
• Hepatic impairment: Dosage adjustment may be necessary

Overdosage

• Symptoms: Severe hypotension, bradycardia, heart failure, bronchospasm, seizures
• Treatment: Supportive care, including intravenous fluids, vasopressors (e.g., dopamine, norepinephrine), atropine for bradycardia, bronchodilators for bronchospasm, and anticonvulsants for seizures

Brand Names

• Lopressor (metoprolol tartrate)
• Toprol-XL (metoprolol succinate)

Monitoring Parameters

• Blood pressure
• Heart rate
• ECG
• Signs and symptoms of heart failure
• Renal and hepatic function tests periodically

Patient Education

• Instruct patients to take medication as prescribed and not to discontinue abruptly.
• Advise patients to monitor their blood pressure and heart rate regularly.
• Inform patients about potential side effects and what to do if they occur.
• Advise patients to avoid alcohol, which may increase the hypotensive effects of metoprolol.
• Instruct patients to inform their healthcare provider if they have any new or worsening symptoms.
• Caution patients about driving or operating machinery until they know how the medication affects them.

Explore metoprolol, a beta-1 selective adrenergic blocking agent, reviewing its indications like hypertension and angina. Learn about its mechanism, pharmacokinetics, and appropriate dosages for various conditions.