Metoprolol Succinate
Metoprolol Succinate
Generic Name
Metoprolol Succinate
Mechanism
Metoprolol Succinate is a β1‑selective adrenergic antagonist.
• Binds competitively to β1‑adrenergic receptors in cardiac tissue.
• Blocks catecholamine‑induced stimulation, ↓ heart rate, contractility, and renin release.
• Reduces myocardial oxygen demand and prolongs diastolic filling time.
Pharmacokinetics
- Absorption: Oral bioavailability ≈ 33 % (first‑pass hepatic metabolism).
- Onset: 1–2 h post‑dose; peak plasma levels 4–6 h.
- Distribution: Highly protein‑bound (≈ 87 % to albumin).
- Metabolism: Primarily CYP2D6 oxidized; metabolites inactive.
- Excretion: Mainly renal (≈ 30 %) and fecal.
- Half‑life: 6–7 h (extended‑release formulation extended to ~12 h).
Indications
- Hypertension (once daily, extended‑release).
- Stable angina pectoris (once daily, extended‑release).
- Heart failure with reduced ejection fraction (HFrEF) (maintenance therapy).
- Post‑myocardial infarction (secondary prevention) when β1‑selectivity is preferred.
Contraindications
- Absolute Contraindications:
- Severe bradycardia (HR < 45 bpm).
- Second‑ or third‑degree AV block without pacemaker.
- Cardiogenic shock or severe heart failure decompensation.
- Relative Contraindications:
- Severe asthma or chronic obstructive pulmonary disease (if using non‑selective β‑blockers).
- Symptomatic hypoglycemia risk in diabetics (masking).
- Warnings:
- Use cautious titration in patients with COPD, peripheral vascular disease, or diabetes.
- Potential for masking angina or arrhythmia if under‑dosage.
Dosing
| Condition | Starting Dose | Titration | Maintenance |
| Hypertension (ER) | 100 mg PO q24 h | ↑ 100 mg every 2 weeks | 200–400 mg q24 h (max 400 mg) |
| Stable angina (ER) | 200 mg PO q24 h | ↑ 200 mg every 2‑4 weeks | 400–600 mg q24 h (max 600 mg) |
| HFrEF | 12.5 mg PO q24 h (ER) | ↑ 25 mg every 2 weeks | 200–400 mg q24 h (max 400 mg) |
| Post‑MI (ER) | 100 mg PO q24 h | ↑ 100 mg every 2‑4 weeks | 200–400 mg q24 h |
• Administration: Oral, once daily with water.
• Special Populations: Dose adjustment for severe hepatic impairment; no adjustment needed for mild‑moderate renal impairment.
Adverse Effects
Common (≥ 10 %)
• Fatigue, dizziness, headache.
• Bradycardia, hypotension, postural dizziness.
Serious (≤ 1 %)
• Severe bradyarrhythmias, AV block, heart failure exacerbation.
• Severe hypotension, bronchospasm in susceptible patients.
Other Notable Adverse Effects
• Metabolic: hypoglycemia (masking symptoms), lipid abnormality.
• Gastrointestinal: nausea, constipation.
Monitoring
- Vital signs: HR, BP (pre‑injection and 1‑2 h post‑dose).
- ECG: baseline and every 2–4 weeks during titration.
- Renal function: eGFR at baseline, 3 months, annually.
- Liver enzymes: baseline, 3 months, annually if hepatic involvement.
- Blood glucose: baseline and regular monitoring in diabetics.
- Weight & NYHA class (for HFrEF).
Clinical Pearls
- Extended‑Release Advantage: Once‑daily dosing improves adherence, especially in chronic heart failure.
- Bradycardia Alert: In hypertensive patients, monitor HR < 50 bpm; consider dose reduction or switching to a non‑β blocker.
- Beta‑Blocker Wash‑Out: When switching from a short‑acting to ER formulation, maintain the same daily dose to avoid sub‑therapeutic levels during the transition.
- Hypoglycemia Masking: In diabetic patients, use glucose monitoring every 4‑6 h during titration; beware of silent hypoglycemia.
- Drug‑Drug Interactions: Avoid concurrent use with strong CYP2D6 inhibitors (e.g., fluoxetine, paroxetine) as they can increase metoprolol plasma levels and risk of bradycardia.
- Pediatric Use: Not approved for children; if used off‑label, start at 1 mg/kg/day and titrate cautiously.
- Storage: Store at room temperature; protect from light.
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• *Referenced by UpToDate, FDA package insert, and drug approval literature. Use when preparing exam questions or patient counseling.*