Lopressor - Drug Monograph

Introduction

Lopressor (metoprolol tartrate) is a cardioselective beta-1 adrenergic receptor blocking agent widely used in cardiovascular medicine. Developed by Ciba-Geigy (now Novartis) and first approved by the FDA in 1978, it remains a cornerstone therapy for various cardiovascular conditions including hypertension, angina pectoris, and heart failure. As a first-generation beta-blocker, Lopressor has established efficacy and safety profiles supported by decades of clinical use and evidence.

Mechanism of Action

Loposterone competitively blocks beta-1 adrenergic receptors primarily in the heart, with minimal effect on beta-2 receptors at therapeutic doses. This selective blockade results in:

• Decreased heart rate (negative chronotropy)
• Reduced myocardial contractility (negative inotropy)
• Slowed atrioventricular conduction
• Decreased cardiac output
• Reduced renin secretion from renal juxtaglomerular cells

These pharmacological effects collectively lower blood pressure, reduce myocardial oxygen demand, and decrease cardiac workload.

Indications

FDA-approved indications:

• Hypertension (monotherapy or combination therapy)
• Angina pectoris (chronic stable angina)
• Secondary prevention following myocardial infarction

Off-label uses (supported by clinical evidence):

• Supraventricular tachycardia
• Atrial fibrillation/flutter rate control
• Migraine prophylaxis
• Essential tremor
• Symptomatic treatment in hypertrophic cardiomyopathy

Dosage and Administration

• Initial dose: 50 mg twice daily or 100 mg once daily (extended-release)
• Maintenance: 100-450 mg daily in divided doses

• Initial: 50 mg twice daily
• Maintenance: 100-400 mg daily in divided doses

• 50 mg every 6 hours for 48 hours, then 100 mg twice daily

• Renal impairment: No dosage adjustment typically needed
• Hepatic impairment: Use with caution; consider reduced doses
• Geriatric: Start with lower doses due to increased sensitivity
• Pediatric: Safety and effectiveness not established

Pharmacokinetics

Contraindications

• Severe bradycardia (heart rate <45-50 bpm)
• Second- or third-degree heart block (without pacemaker)
• Cardiogenic shock
• Decompensated heart failure
• Sick sinus syndrome
• Severe peripheral arterial disorders
• Hypersensitivity to metoprolol or components
• Concurrent use with certain antipsychotics (e.g., thioridazine)

Warnings and Precautions

• May precipitate heart failure in susceptible patients
• Abrupt withdrawal can cause rebound hypertension, angina exacerbation, or MI
• Can mask tachycardia in hypoglycemia

• Use caution in patients with asthma/COPD due to potential bronchoconstriction
• Generally safer than non-selective beta-blockers in respiratory disease

• May mask signs of hypoglycemia in diabetics
• Can affect lipid metabolism (increases triglycerides, decreases HDL)

• Use caution in patients with pheochromocytoma (requires alpha-blockade first)
• May exacerbate myasthenia gravis symptoms
• Reduced clearance in CYP2D6 poor metabolizers

Drug Interactions

• Verapamil, diltiazem: Additive bradycardia and AV block
• Clonidine: Exaggerated rebound hypertension upon withdrawal
• Antiarrhythmics (digoxin, amiodarone): Enhanced bradycardic effects
• CYP2D6 inhibitors (fluoxetine, paroxetine): Increased metoprolol concentrations
• Insulin/oral hypoglycemics: Masked hypoglycemia symptoms

• NSAIDs: May reduce antihypertensive effect
• Sympathomimetics: Counteract beta-blockade effects
• Antipsychotics: Increased risk of hypotension/bradycardia

Adverse Effects

• Fatigue
• Dizziness
• Depression
• Bradycardia
• Hypotension
• Diarrhea

• Bronchospasm
• Cold extremities
• Sleep disturbances
• Nausea
• Dyspnea

• AV block
• Heart failure exacerbation
• Hallucinations
• Peyronie's disease
• Thrombocytopenia

Monitoring Parameters

• Blood pressure and heart rate
• ECG (especially for conduction abnormalities)
• Renal and hepatic function
• Blood glucose (in diabetics)

• Blood pressure and heart rate at each visit
• Signs/symptoms of heart failure
• Respiratory status in patients with lung disease
• Mental status changes
• Exercise tolerance in angina patients

• Lipid profile (annually)
• Blood glucose monitoring in diabetics

Patient Education

• Do not abruptly discontinue medication; taper under medical supervision
• Take with food to enhance absorption
• Monitor blood pressure and pulse as directed
• Report unusual weight gain, edema, or shortness of breath
• Be aware of potential dizziness, especially when standing quickly
• Inform all healthcare providers about Lopressor use before procedures
• Use caution with alcohol and other CNS depressants
• Diabetics should monitor blood glucose carefully
• Notify provider if pregnancy is planned or suspected

References

1. Frishman WH. Metoprolol: A New Generation of Beta-Blocker. J Clin Pharmacol. 2017;57(12):1499-1505. 2. FDA Prescribing Information: Lopressor (metoprolol tartrate). 2022. 3. Wiysonge CS, et al. Beta-blockers for hypertension. Cochrane Database Syst Rev. 2017;1:CD002003. 4. The CAPRICORN Investigators. Effect of carvedilol on outcome after myocardial infarction in patients with left-ventricular dysfunction. Lancet. 2001;357(9266):1385-1390. 5. Cruickshank JM. The modern role of beta-blockers in cardiovascular medicine. Prog Cardiovasc Dis. 2018;60(4-5):475-484. 6. McDonagh TA, et al. 2021 ESC Guidelines for the diagnosis and treatment of acute and chronic heart failure. Eur Heart J. 2021;42(36):3599-3726. 7. Whelton PK, et al. 2017 ACC/AHA/AAPA/ABC/ACPM/AGS/APhA/ASH/ASPC/NMA/PCNA Guideline for the Prevention, Detection, Evaluation, and Management of High Blood Pressure in Adults. J Am Coll Cardiol. 2018;71(19):e127-e248.