Metoprolol

Drug Information: Metoprolol

Metoprolol is a selective beta-1 adrenergic receptor blocker commonly used in the management of various cardiovascular conditions. It belongs to the class of beta-blockers, specifically targeting the beta-1 receptors primarily found in the heart. By blocking these receptors, metoprolol reduces heart rate, blood pressure, and myocardial contractility. This makes it effective in treating conditions such as hypertension, angina pectoris, heart failure, and certain arrhythmias. Metoprolol is available in both immediate-release (tartrate) and extended-release (succinate) formulations, allowing for flexible dosing regimens tailored to individual patient needs. It is crucial to monitor patients on metoprolol for potential side effects such as bradycardia, hypotension, and fatigue. Abrupt discontinuation of metoprolol should be avoided to prevent rebound hypertension or angina.

Category

Drugs for ACS

Mechanism of Action

Metoprolol functions primarily as a selective beta-1 adrenergic receptor blocker. Beta-1 receptors are predominantly located in the heart, where they mediate the effects of catecholamines (such as epinephrine and norepinephrine) on heart rate, contractility, and conduction velocity. By competitively binding to these receptors, metoprolol blocks the effects of these catecholamines. This results in a decrease in heart rate (negative chronotropy), a reduction in the force of myocardial contraction (negative inotropy), and a slowing of atrioventricular (AV) conduction. The decreased heart rate reduces myocardial oxygen demand, while the reduced contractility lowers blood pressure and further decreases cardiac workload. In the context of Acute Coronary Syndrome (ACS), this mechanism helps to stabilize the heart, reduce ischemia, and prevent further cardiac events. The selectivity for beta-1 receptors, compared to beta-2 receptors (found in the lungs and peripheral vasculature), aims to minimize potential side effects such as bronchospasm, although this selectivity is not absolute and can diminish at higher doses.

Clinical Uses

Metoprolol is a widely used beta-blocker with several important clinical applications, particularly in the management of Acute Coronary Syndrome (ACS). In ACS, metoprolol helps to reduce myocardial oxygen demand, limit infarct size, and prevent life-threatening arrhythmias. It is often administered early in the course of ACS, provided there are no contraindications. Beyond ACS, metoprolol is a mainstay in the treatment of hypertension, both as monotherapy and in combination with other antihypertensive agents. It is also used to manage angina pectoris, reducing the frequency and severity of chest pain by decreasing cardiac workload. In patients with heart failure, specifically chronic heart failure with reduced ejection fraction (HFrEF), metoprolol succinate (extended-release) has been shown to improve survival and reduce hospitalizations when used in conjunction with other guideline-directed medical therapies. Additionally, metoprolol can be used to control certain types of arrhythmias, such as supraventricular tachycardia and atrial fibrillation, by slowing the heart rate and improving cardiac rhythm stability. It is also sometimes used off-label for conditions like migraine prophylaxis and essential tremor.

Dosage

Adult Dosage:

• Hypertension: Metoprolol tartrate: 50-100 mg orally twice daily, may increase gradually up to 200 mg twice daily. Metoprolol succinate ER: 25-100 mg orally once daily, may increase gradually up to 200 mg once daily.
• Angina Pectoris: Metoprolol tartrate: 50 mg orally twice daily, may increase gradually up to 200 mg twice daily. Metoprolol succinate ER: 100 mg orally once daily, may increase gradually.
• Acute Coronary Syndrome (ACS): IV: 5 mg IV bolus every 2-5 minutes for 3 doses, followed by oral Metoprolol tartrate 50 mg every 6 hours for 48 hours then 100 mg twice daily.
• Heart Failure (HFrEF): Metoprolol succinate ER: Initial dose 12.5 mg or 25mg orally once daily, titrate slowly every 2 weeks to the highest tolerated dose, not to exceed 200 mg daily.

Pediatric Dosage:

• Dosage must be determined by a physician and adjusted based on patient weight and clinical response. Consult pediatric-specific dosing guidelines.

Indications

Common indications for Metoprolol include:

• Hypertension
• Angina Pectoris
• Acute Coronary Syndrome (ACS)
• Heart Failure (HFrEF)
• Supraventricular Tachycardia
• Atrial Fibrillation/Flutter (rate control)
• Migraine Prophylaxis (off-label)
• Essential Tremor (off-label)

Contraindications

Metoprolol is contraindicated in the following conditions:

• Severe Bradycardia (heart rate less than 50 bpm)
• Second- or Third-Degree AV Block (without a pacemaker)
• Sick Sinus Syndrome (unless a permanent pacemaker is in place)
• Decompensated Heart Failure
• Cardiogenic Shock
• Severe Peripheral Arterial Disease
• Hypotension (systolic blood pressure less than 100 mmHg)
• Known hypersensitivity to Metoprolol or other beta-blockers
• Acute Asthma Exacerbation or Severe COPD (relative contraindication; use with caution)
• Pheochromocytoma (unless alpha-blocker is also administered)

FAQ

1. What is Metoprolol used for?
   Metoprolol is used to treat high blood pressure, angina (chest pain), and heart failure. It can also be used after a heart attack to improve survival.
2. How does Metoprolol work?
   Metoprolol blocks the effects of adrenaline on the heart, slowing down the heart rate and reducing the force of heart muscle contraction. This lowers blood pressure and reduces the heart’s workload.
3. What are the common side effects of Metoprolol?
   Common side effects include fatigue, dizziness, slow heart rate, and low blood pressure. Some people may also experience cold hands and feet.
4. Can I suddenly stop taking Metoprolol?
   No, it is important not to stop taking Metoprolol suddenly. Abruptly stopping the medication can cause rebound hypertension, angina, or even a heart attack. The medication should be gradually reduced under the guidance of a healthcare provider.
5. What should I do if I miss a dose of Metoprolol?
   If you miss a dose, take it as soon as you remember. However, if it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not double the dose to catch up.
6. Does Metoprolol interact with other medications?
   Yes, Metoprolol can interact with several medications, including other blood pressure medications, certain antidepressants, and some heart medications. It is important to inform your doctor about all the medications you are taking.
7. Can I drink alcohol while taking Metoprolol?
   Alcohol can increase the blood pressure-lowering effects of Metoprolol, potentially causing dizziness or lightheadedness. It is best to avoid or limit alcohol consumption while taking this medication.
8. Will Metoprolol affect my ability to exercise?
   Metoprolol can lower your heart rate, which may affect your exercise tolerance. Talk to your doctor about a safe exercise plan while taking this medication.