Usage
S-Metoprolol tartrate is primarily prescribed for the management of hypertension (high blood pressure), angina pectoris (chest pain), and following a myocardial infarction (heart attack) to reduce cardiovascular mortality. It is also used to treat and prevent certain types of irregular heartbeats (arrhythmias) such as supraventricular tachycardia, and for migraine prophylaxis. It belongs to the pharmacological class of cardioselective beta-1 adrenergic receptor blockers, commonly known as beta-blockers. Its mechanism of action involves selectively blocking beta-1 receptors in the heart, reducing heart rate, contractility, and cardiac output, thus lowering blood pressure and myocardial oxygen demand.
Alternate Names
S-Metoprolol is sometimes referred to simply as Metoprolol tartrate. Brand names include Lopressor and Toprol XL (extended-release formulation containing Metoprolol succinate, not S-Metoprolol tartrate).
How It Works
Pharmacodynamics: S-Metoprolol lowers blood pressure by reducing cardiac output through beta-1 receptor blockade in the heart, decreasing heart rate and contractility. It also inhibits renin release from the kidneys, contributing to the antihypertensive effect. It decreases myocardial oxygen demand, relieving angina symptoms.
Pharmacokinetics: S-Metoprolol is well-absorbed orally. It is extensively metabolized by the liver, primarily by the CYP2D6 enzyme. The major metabolite, alpha-hydroxymetoprolol, has some beta-blocking activity. S-Metoprolol is predominantly eliminated via renal excretion.
Mode of Action: S-Metoprolol competitively binds to beta-1 adrenergic receptors in cardiac tissue, preventing the binding of catecholamines like norepinephrine and epinephrine. This antagonism of sympathetic stimulation reduces heart rate, myocardial contractility, and conduction velocity, thereby decreasing cardiac output and blood pressure.
Elimination Pathways: Hepatic metabolism is the primary route of elimination, mainly through CYP2D6. Renal excretion is the major pathway for the elimination of metabolites.
Dosage
Standard Dosage
Adults:
- Hypertension: Initial dose is 100 mg daily, administered orally as a single dose or in divided doses. The dose can be increased weekly up to a maximum of 450 mg/day.
- Angina Pectoris: Initial dose is 50 mg twice daily. Maintenance dose is 100-400 mg/day in divided doses.
- Post-Myocardial Infarction: Initially, 5 mg IV every 2 minutes for three doses. Following IV administration, if tolerated, 50 mg orally every 6 hours for 48 hours, followed by 100 mg twice daily orally.
- Migraine Prophylaxis: 100-200 mg daily in divided doses.
Children:
Dosage in children for hypertension is based on body weight, starting at 1 mg/kg/day (up to 50 mg/day initially) with a maximum dose of 2 mg/kg/day (or up to 200 mg/day). The immediate-release form is generally not recommended for children. Extended-release formulations may be used under specialist supervision.
Special Cases:
- Elderly Patients: Start with lower doses and titrate carefully.
- Patients with Renal Impairment: Dose adjustment may be necessary depending on the degree of impairment.
- Patients with Hepatic Dysfunction: Start with lower doses and titrate cautiously as S-Metoprolol is extensively metabolized by the liver.
- Patients with Comorbid Conditions: Careful monitoring and dose adjustment may be required in patients with diabetes, asthma, or other respiratory diseases.
Clinical Use Cases
The following are examples and not exhaustive, dosage needs to be individualized according to patient and situation:
- Intubation: Metoprolol may be used to control heart rate and blood pressure during intubation, specifically IV formulations.
- Surgical Procedures: May be administered pre-operatively or intra-operatively to manage hypertension and tachycardia. IV formulations are generally used in these situations.
- Mechanical Ventilation: May be used to control heart rate and blood pressure in ventilated patients, again focusing on IV formulations.
- Intensive Care Unit (ICU) Use: Commonly used in the ICU setting for hemodynamic management, IV formulations preferred.
- Emergency Situations: In hypertensive emergencies or acute coronary syndromes, intravenous S-Metoprolol may be used for rapid control of blood pressure and heart rate.
Dosage Adjustments:
Dose adjustments are based on patient response, renal function, hepatic function, and concomitant medications.
Side Effects
Common Side Effects:
Fatigue, dizziness, bradycardia, hypotension, diarrhea, nausea, and shortness of breath.
Rare but Serious Side Effects:
Heart block, worsening heart failure, bronchospasm, and severe allergic reactions.
Long-Term Effects:
Mask symptoms of hypoglycemia in diabetics, sexual dysfunction.
Adverse Drug Reactions (ADR):
Severe bradycardia, hypotension, heart failure exacerbation, bronchospasm requiring immediate medical intervention.
Contraindications
Severe bradycardia, second or third-degree heart block, cardiogenic shock, decompensated heart failure, severe peripheral arterial circulatory disorders, sick sinus syndrome (unless a permanent pacemaker is in place), untreated pheochromocytoma.
Drug Interactions
- CYP450 Interactions: Metoprolol is metabolized by CYP2D6. Inhibitors of CYP2D6 (e.g., fluoxetine, paroxetine, quinidine) can increase metoprolol levels. Inducers of CYP2D6 (e.g., rifampicin) can decrease metoprolol levels.
- Other Interactions: Calcium channel blockers, digoxin, clonidine, insulin, and oral hypoglycemic agents.
Pregnancy and Breastfeeding
- Pregnancy Safety Category: Category C. Metoprolol should only be used during pregnancy if the potential benefit justifies the potential risk to the fetus.
- Breastfeeding: Metoprolol is excreted in breast milk. Monitor infants for signs of beta-blockade (e.g., bradycardia, hypotension).
Drug Profile Summary
- Mechanism of Action: Cardioselective beta-1 adrenergic receptor blocker.
- Side Effects: Fatigue, dizziness, bradycardia, hypotension.
- Contraindications: Severe bradycardia, heart block, heart failure.
- Drug Interactions: CYP2D6 inhibitors, calcium channel blockers, digoxin.
- Pregnancy & Breastfeeding: Use with caution. Category C.
- Dosage: Hypertension: 100-450 mg/day; Angina: 100-400 mg/day.
- Monitoring Parameters: Heart rate, blood pressure, EKG.
Popular Combinations
Metoprolol is frequently combined with other antihypertensives like hydrochlorothiazide or other diuretics for synergistic blood pressure control.
Precautions
- Monitor for bradycardia, hypotension, heart block, and bronchospasm.
- Use with caution in patients with asthma, diabetes, or peripheral vascular disease.
- Avoid abrupt discontinuation.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for S-Metoprolol Tartrate?
A: Dosage depends on the indication. For hypertension, the initial dose is typically 100 mg/day, adjustable up to 450 mg/day. For angina, the usual dose is 100-400 mg/day in divided doses.
Q2: How should S-Metoprolol be administered?
A: Orally, with or immediately after meals.
Q3: Can S-Metoprolol be used in patients with asthma?
A: Use with caution in asthmatics due to the potential for bronchospasm. Cardioselective beta-blockers like S-Metoprolol are generally preferred over non-selective beta-blockers if a beta-blocker is necessary.
Q4: What are the common side effects of S-Metoprolol?
A: Fatigue, dizziness, bradycardia, and hypotension are common side effects.
Q5: Does S-Metoprolol interact with other medications?
A: Yes. It can interact with calcium channel blockers, digoxin, clonidine, CYP2D6 inhibitors (like fluoxetine, paroxetine).
Q6: Can S-Metoprolol be used during pregnancy?
A: It is a pregnancy category C drug. Use only if the potential benefit outweighs the risk to the fetus.
A: Primarily by the liver, specifically the CYP2D6 enzyme.
Q8: What are the contraindications for S-Metoprolol?
A: Severe bradycardia, heart block, cardiogenic shock, decompensated heart failure.
Q9: Should S-Metoprolol be discontinued abruptly?
A: No. Taper the dose gradually to avoid rebound hypertension or worsening of angina.
Q10: How is S-Metoprolol different from Metoprolol succinate?
A: S-Metoprolol tartrate is the immediate-release formulation, while Metoprolol succinate is the extended-release formulation. They have different pharmacokinetic profiles but similar pharmacodynamic effects.
