Can Metoprolol ER Be Split in Half?
No—extended-release metoprolol succinate tablets should not be split, even when a lower dose is needed, because splitting destroys the controlled-release mechanism and creates unpredictable drug delivery.
Why Splitting Extended-Release Metoprolol Is Unsafe
Controlled-Release Technology Is Destroyed by Splitting
- Metoprolol succinate ER is formulated as a multiple-unit pellet system embedded in a tablet matrix, designed to release metoprolol at a near-constant rate over approximately 20 hours. 1
- Splitting the tablet disrupts this controlled-release mechanism, causing immediate release of a portion of the drug and creating marked peaks and troughs in plasma concentration—the exact problem the ER formulation was designed to avoid. 1
- Even though some metoprolol ER tablets are scored, research demonstrates that the pellets are not uniformly distributed throughout the tablet, so splitting produces highly variable drug content in each half (some halves contain significantly more or less than 50% of the labeled dose). 2
Evidence Against Splitting Extended-Release Formulations
- A 2010 study using near-infrared chemical imaging showed that metoprolol succinate pellets are non-homogeneously distributed on tablet surfaces, resulting in large variations in weight and content uniformity when tablets are split. 2
- Splitting extended-release tablets can result in uncontrolled release of the active ingredient, leading to overdose risk or loss of therapeutic effect. 3, 4
- Destroying the extended-release coating by splitting can cause degradation of the compound and eliminate the 24-hour coverage that once-daily dosing provides. 3
What to Do Instead: Use Immediate-Release Metoprolol Tartrate
Switch to Metoprolol Tartrate for Flexible Low-Dose Titration
- For a 75-year-old woman with bradycardia (~50 bpm), chronic kidney disease stage 3a, and dizziness, the safest approach is to switch from metoprolol succinate ER to metoprolol tartrate (immediate-release) at a very low starting dose of 12.5 mg twice daily. 5
- Metoprolol tartrate is available in 25 mg tablets that can be split in half to achieve 12.5 mg doses, because immediate-release tablets do not have a controlled-release mechanism that would be disrupted by splitting. 5
- The American College of Cardiology explicitly recommends starting at 12.5 mg in patients with concerns about beta-blocker tolerance, including those with borderline bradycardia or dizziness. 5
Dosing Strategy for This High-Risk Patient
- Start metoprolol tartrate 12.5 mg twice daily (split a 25 mg tablet in half). 5
- Monitor heart rate and blood pressure at each visit, targeting a resting heart rate of 50–60 bpm unless limiting side effects occur. 5
- If the patient tolerates 12.5 mg twice daily without worsening bradycardia or dizziness, the dose can be increased by 12.5–25 mg increments every 1–2 weeks as needed for blood pressure control. 5
- Hold the dose if systolic blood pressure drops below 100 mmHg with symptoms or if heart rate falls below 50 bpm with dizziness. 5
Critical Safety Considerations in This Patient
Absolute Contraindications to Verify
- Symptomatic bradycardia (heart rate <50–60 bpm with dizziness) is an absolute contraindication to continued beta-blocker therapy. 5
- This patient's resting heart rate of ~50 bpm with occasional dizziness places her at the threshold of symptomatic bradycardia, so metoprolol should be used with extreme caution or avoided entirely if dizziness worsens. 5
- The European Society of Cardiology identifies symptomatic bradycardia as a contraindication to beta-blocker therapy in patients with coronary artery disease or heart failure. 5
Monitoring Parameters After Initiation
- Assess heart rate, blood pressure, and symptoms (especially dizziness) within 1–2 weeks after starting metoprolol tartrate 12.5 mg twice daily. 5
- Watch specifically for symptomatic bradycardia (heart rate <60 bpm with dizziness or lightheadedness) and symptomatic hypotension (systolic BP <100 mmHg with dizziness or blurred vision). 5
- If dizziness worsens or heart rate drops below 45 bpm, reduce the dose by 50% or hold the medication entirely and reassess within 1–2 days. 5
Common Pitfalls to Avoid
- Do not split metoprolol succinate ER tablets to achieve a 12.5 mg dose—this creates unpredictable drug delivery and eliminates 24-hour coverage. 1, 2
- Do not abruptly discontinue metoprolol if the patient cannot tolerate it; taper by reducing the dose by 25–50% every 1–2 weeks to prevent rebound hypertension or worsening angina. 5
- Do not assume that a scored tablet is safe to split—metoprolol ER tablets are scored but should not be split due to non-uniform pellet distribution. 2
- Do not rely on resting heart rate alone to judge beta-blocker tolerance; assess for symptoms (dizziness, syncope, fatigue) at each visit. 5
Alternative: Consider Reducing or Discontinuing Beta-Blocker Therapy
When to Hold Metoprolol Completely
- If this patient's dizziness is clearly related to bradycardia (heart rate consistently <50 bpm with symptoms), metoprolol should be held entirely rather than attempting to split ER tablets or use very low doses. 5
- The ACC/AHA perioperative guidelines specify holding beta-blockers when heart rate is consistently below 45 bpm, or delaying administration by 12 hours when heart rate is 45–49 bpm. 5
- Complete discontinuation of metoprolol increases 1-year mortality risk 2.7-fold compared to continuous use, so if the drug must be stopped, taper gradually over 1–2 weeks. 5
Alternative Antihypertensive Strategy
- For a 75-year-old woman with hypertension, aortic arteriosclerosis, and CKD stage 3a, an ACE inhibitor or ARB is a more appropriate first-line agent than a beta-blocker, especially given her bradycardia and dizziness. 5
- If rate control is needed for atrial fibrillation or another indication, consider diltiazem 120–360 mg daily as an alternative to metoprolol, though this should be avoided if she has heart failure with reduced ejection fraction. 5