Lopressor
Lopressor
Generic Name
Lopressor
Mechanism
Lopressor competitively blocks β1‑adrenergic receptors in:
• Heart: ↓heart rate, ↓contractility, ↓myocardial oxygen demand
• Peripheral vasculature: reflex vasoconstriction mitigated by sustained β1‑blockade
Resulting effects: reduced blood pressure, decreased anginal episodes, slowed ventricular rate in arrhythmias, and improved post‑MI remodeling.
Pharmacokinetics
- Absorption: Oral bioavailability ≈ 50 % (metoprolol succinate ~40 – 60 %) due to first‑pass hepatic metabolism.
- Distribution: V_d ≈ 2 L/kg; highly protein‑bound (~90 %).
- Metabolism: Primarily CYP2D6; poor metabolizers show ↑serum levels, ↑bradycardia risk.
- Elimination: Half‑life 3 – 4 h (tartrate) vs. 12 – 14 h (succinate ER). Renal excretion (~45 %) and hepatic (~25 %).
- Drug interactions: CYP2D6 inhibitors (e.g., fluoxetine) ↑ toxicity; ß‑agonists may blunt efficacy.
Indications
- Hypertension: Additive BP control in combination therapy.
- Stable angina: ↓ischemic episodes.
- Acute MI (post‑reperfusion): ↓mortality, myocardial remodeling.
- Heart failure (CHF): Improved survival, reduced hospitalization.
- Sinus/supine tachycardia and atrial fibrillation rate control.
- Pre‑anesthesia: Successful rate and rhythm control in the perioperative setting.
Contraindications
- Absolute contraindications:
- Severe bradycardia (HR < 50 bpm)
- Second‑/third‑degree AV block without pacing
- Cardiogenic shock or acute decompensated heart failure
- Severe hypotension (SBP < 90 mm Hg)
- Relative contraindications:
- Advanced COPD or uncontrolled asthma
- Severe hepatic/renal insufficiency (dose adjustment)
- Uncontrolled peptic ulcer disease
- Warnings:
- Monitor for bronchospasm in susceptible patients.
- Periodic assessment of glycemic control; avoid in uncontrolled diabetes.
- Possible depression or sleep disturbances; discuss with patient.
Dosing
| Formulation | Typical Dose (Sea‑to‑Sea) | Frequency | Special Notes |
| Metoprolol Tartrate (immediate‑release) | 25–100 mg PO QD–QID | 2–4 times daily | Short acting; titrate to BP/HR. |
| Metoprolol Succinate (extended‑release) | 25–100 mg PO QD | 1× daily | Once‑daily dosing; start with low dose, titrate up to ≤200 mg/day. |
| IV (for cardio‑stabilization) | 5–10 mg IV over 2 min, repeat q10 min up to 40 mg | Acute | Initial loading dose; slow titration to avoid hypotension. |
• Start low, go slow: titrate by 25 mg increments every 3–5 days in heart failure or post‑MI.
• Hold: discontinue 24 h before major cardiac surgeries to prevent intra‑operative BP collapse.
• Food factor: oral succinate should be taken with food to minimize GI upset; tartrate may be taken without food.
Monitoring
- Vital signs: HR, BP (supine & standing) at ≥7‑day intervals until stable.
- ECG: baseline, and after dose escalation to detect rates & new QRS changes.
- Serum: CBC, renal & hepatic panels during early titration.
- Blood glucose: baseline and quarterly in diabetics.
- Functional status: NYHA class for heart failure; NYHA improved by ≥1 class = success.
Clinical Pearls
- CYP2D6 poor metabolizers: begin with 25 mg BID; monitor heart rate closely.
- Morning dosing reduces nocturnal tachycardia and improves sleep quality.
- Extended‑release vs. immediate: ER offers stable plasma levels and fewer BP dips; tartrate preferred for rapid HR control.
- Metoprolol + digoxin: monitor for bradycardia; adjust digoxin dose accordingly.
- Post‑MI regimen: evidence supports early initiation within 24 h of reperfusion therapy; improves 1‑year survival.
- Asthma/COPD cautions: use lowest effective dose; consider albuterol availability.
- Mental health: report mood changes; avoid concomitant serotonergic drugs that may potentiate depressive side‑effects.
- Orthostatic hypotension: advise patients to rise slowly; educate on symptoms of fainting.
*For more in‑depth discussion on pharmacodynamic nuances and patient‑specific titration algorithms, reference contemporary United States National Institute of Health guidelines (2024) and the 2023 ESC Guidelines on Heart Failure.*