Metoprolol Tartrate for Intermittent Tachycardia
For intermittent tachycardia requiring as-needed use, metoprolol tartrate (immediate-release) is the appropriate choice, not metoprolol succinate (extended-release). 1
Pharmacological Rationale
Metoprolol tartrate is the immediate-release formulation with rapid onset of action, making it suitable for acute symptom control. 1 The American College of Cardiology recommends metoprolol tartrate at 25-100 mg twice daily for rate control in various tachyarrhythmias, while metoprolol succinate is dosed 50-400 mg once daily for chronic maintenance therapy. 1
The key distinction is that tartrate provides immediate effect for symptomatic episodes, whereas succinate is designed for sustained 24-hour coverage and is not appropriate for "as-needed" dosing. 1, 2
Clinical Application for Intermittent Tachycardia
Acute Symptomatic Episodes
For acute treatment of supraventricular tachycardia in hemodynamically stable patients, the American College of Cardiology recommends intravenous metoprolol (5 mg over 1-2 minutes, repeated every 5 minutes as needed, maximum 15 mg total). 1, 3
After IV administration, oral metoprolol tartrate can be initiated 15 minutes after the last IV dose at 25-50 mg every 6 hours. 2, 3
Oral As-Needed Strategy
For patients with intermittent episodes, metoprolol tartrate 25-50 mg can be taken at symptom onset. 2 Research demonstrates that oral metoprolol effectively converts supraventricular tachycardia to sinus rhythm in 50% of cases and significantly reduces ventricular rate in others. 4
In multifocal atrial tachycardia, oral metoprolol 25-50 mg restored sinus rhythm in all 11 patients within 1-3 hours, with mean ventricular rate reduction from 131 to 87 beats per minute. 5
Critical Contraindications Before Each Dose
Before administering metoprolol tartrate for acute tachycardia, verify absence of: 1, 2
- Signs of decompensated heart failure, low output state, or pulmonary congestion
- Systolic blood pressure <100 mmHg with symptoms
- Heart rate <60 bpm (if already bradycardic despite tachycardia symptoms)
- Second or third-degree AV block without functioning pacemaker
- Active asthma or severe reactive airway disease
- Pre-excited atrial fibrillation (Wolff-Parkinson-White syndrome)
Why Metoprolol Succinate is Inappropriate
Metoprolol succinate is an extended-release formulation designed for once-daily dosing with sustained drug levels over 24 hours. 1, 2 This pharmacokinetic profile makes it unsuitable for as-needed use because:
- It takes hours to reach therapeutic levels, providing no immediate symptom relief 1
- The extended-release mechanism cannot be "turned off" if adverse effects develop 2
- It is specifically designed for chronic conditions requiring continuous rate control, not episodic symptoms 1
Monitoring After Administration
- Check blood pressure and heart rate 30-60 minutes after oral tartrate administration 2
- Watch for symptomatic bradycardia (heart rate <60 bpm with dizziness) or hypotension (systolic BP <100 mmHg with symptoms) 1
- Listen for new bronchospasm, particularly in patients with any history of reactive airway disease 2
Common Pitfall to Avoid
Never use metoprolol succinate for as-needed dosing. 1 The extended-release formulation is exclusively for chronic daily therapy in conditions like hypertension, heart failure, or persistent atrial fibrillation requiring continuous rate control. 1, 2 Attempting to use it for intermittent symptoms will result in inadequate acute symptom control and unnecessary drug exposure between episodes.