Metoprolol – heart rate control

 

1. Mechanism & Class

• Class: β₁-Selective Beta-Blocker (Cardioselective)

• Action:

  • Blocks cardiac β₁-receptors → ↓ sinus node firing rate and AV conduction

  • Reduces resting/peak heart rate (HR), myocardial oxygen demand

• Formulations:

  • Tartrate (IR): Short-acting (dosed BID) - Lopressor®

  • Succinate (ER): 24-hour control - Toprol-XL®

---

2. Key Indications for Rate Control

Condition	Target HR	Formulation
Atrial Fibrillation (AFib)	60-100 bpm	Tartrate BID
Sinus Tachycardia	60-100 bpm	Succinate daily
Post-MI Tachycardia	50-60 bpm	Tartrate BID → Succinate
SVT	Acute IV → PO	IV/PO Tartrate

---

3. Dosing Protocols

Scenario	Initial Dose	Titration	Max Dose
Chronic AFib	Tartrate 25 mg BID	↑ by 25 mg BID q3-7d	100 mg BID
Acute SVT/AFib (IV)	2.5-5 mg IV slow	Repeat q5min × 3	15 mg
Post-MI	Tartrate 25 mg BID → Switch to Succinate 100 mg daily		200 mg/day
Anxiety-Induced Tachycardia	Succinate 25 mg daily	↑ 25 mg weekly	200 mg/day

Goal HR: 55-65 bpm for most conditions (avoid <50 bpm)

---

4. Critical Warnings

Risk	Management
Bradycardia/Heart Block	Hold if HR <50 bpm or SBP <90 mmHg
Acute HF Decompensation	Avoid in decompensated HF (unless tachycardic)
Bronchospasm	Use cautiously in asthma/COPD (low-dose trial)
Masked Hypoglycemia	Caution in diabetics (↓ tremor/tachycardia)
Abrupt Withdrawal	Taper over 1-2 weeks (↑ rebound ischemia)

---

5. Drug Interactions

Interacting Drug	Effect	Action
Verapamil/Diltiazem	↑ Bradycardia/AV block	Avoid combo
Digoxin	Additive HR reduction	Monitor ECG
Clonidine	Rebound hypertension on withdrawal	Avoid concurrent use
Insulin/Sulfonylureas	Masked hypoglycemia	Educate patient

---

6. Administration Pearls

• IV Push: Dilute 5 mg in 10 mL NS → infuse over 2-5 min (rapid IV → cardiac arrest).

• Switch IR→ER: Total daily tartrate dose ≈ succinate dose (e.g., 50 mg BID tartrate → 100 mg daily succinate).

• Missed Dose: Skip if >50% late; never double dose (risk of bradycardia).

---

7. Special Populations

Group	Recommendation
Elderly	Start tartrate 12.5 mg BID
CKD/HD	No dose adjustment needed
Hepatic Impairment	↓ Dose 50% (Child-Pugh B/C)
Pregnancy	Category C (use labetalol first)

---

8. Monitoring

• ECG: PR interval >200 ms → reduce dose

• HR/BP: Daily during titration

• Symptoms: Fatigue, dizziness (signs of over-blockade)

---

⚠️ Black Box Warning

• Abrupt Withdrawal: Risk of angina/MI – taper over 1-2 weeks.

---

9. Clinical Alternatives

Situation	Preferred Agent
Asthma/COPD	Cardioselective: Bisoprolol
Advanced HFrEF	Carvedilol
Refractory Tachycardia	Ivabradine

---

Patient Counseling

1. "Check pulse daily – report HR <55 bpm or dizziness."

2. "Never stop suddenly – causes dangerous heart strain."

3. "IV doses given slowly – rapid injection risks collapse."

4. "Diabetics: Monitor glucose closely – may mask low sugar signs."

💡 Pro Tip: For AFib, combine with digoxin for synergistic rate control if monotherapy fails.

Sources: ACC/AHA AFib Guidelines (2023), ESC HF Guidelines (2023)