Can metoprolol tartrate (Lopressor) 12.5 mg twice daily (bid) as needed (PRN) be used to manage tachycardia in a patient with a history of asthma, who is undergoing an Ativan (lorazepam) taper and cannot take propranolol?

Metoprolol Tartrate for Tachycardia Management in a Patient with Asthma During Ativan Taper

Yes, metoprolol tartrate 12.5 mg twice daily PRN can be safely used to manage tachycardia in this patient with asthma who is undergoing an Ativan taper and cannot take propranolol.

Rationale for Using Metoprolol in Asthma Patients

• Metoprolol is a cardioselective (beta-1 selective) beta-blocker that has less effect on bronchial smooth muscle compared to non-selective agents like propranolol, making it safer for patients with asthma 1, 2
• Low doses of cardioselective beta-blockers such as metoprolol are generally well-tolerated in patients with asthma, particularly when the patient is concurrently receiving optimal bronchodilator therapy 2, 3
• Guidelines specifically state that "mild wheezing or a history of chronic obstructive pulmonary disease mandates a short-acting cardioselective agent at a reduced dose (e.g., 12.5 mg of metoprolol orally) rather than the complete avoidance of a beta blocker" 1

Dosing Considerations

• The recommended starting dose of 12.5 mg twice daily PRN is appropriate and aligns with guideline recommendations for patients with respiratory concerns 1, 4
• This low dose minimizes the risk of bronchospasm while still providing benefit for heart rate control 3
• The PRN (as needed) administration allows for flexible dosing based on the patient's symptoms and heart rate 4

Safety Profile in Asthma

• Research shows that metoprolol at low doses (not exceeding 100 mg total daily) can be safely used in asthmatics who require beta-blockade, provided they are on optimal bronchodilator therapy 3
• Studies comparing cardioselective beta-blockers in asthma patients found that metoprolol caused only very slight decreases in pulmonary function 5
• Network meta-analysis data indicates that metoprolol poses less risk of asthma exacerbation than non-selective agents like propranolol, particularly at lower doses 6

Monitoring Recommendations

• Monitor heart rate and blood pressure after administration 1
• Assess for any signs of bronchospasm or worsening asthma symptoms 4
• Target resting heart rate should be 50-60 beats per minute unless limiting side effects occur 1
• If the patient experiences any respiratory distress, discontinue the medication and consider alternative approaches 1

Contraindications and Precautions

• Avoid using metoprolol in patients with:
  • Marked first-degree AV block (PR interval >0.24 s) 1
  • Second or third-degree heart block without a functioning pacemaker 1
  • Severe left ventricular dysfunction or heart failure 1
  • Cardiogenic shock or hypotension (systolic BP <90 mmHg) 1
  • Severe or uncontrolled asthma 2

Alternative Options if Metoprolol is Not Tolerated

• Diltiazem or verapamil (non-dihydropyridine calcium channel blockers) can be considered as alternatives for heart rate control if beta-blockers cannot be tolerated 1
• Digoxin may be considered in some cases, though it is less effective for rate control during periods of increased sympathetic tone 1

Remember that while metoprolol is safer than propranolol in asthma patients, careful monitoring is still essential, especially during the initial administration period. The low dose of 12.5 mg twice daily PRN is an appropriate starting point that balances the need for heart rate control with the risk of bronchospasm.