What dose of metoprolol (Lopressor) should be titrated for a 78-year-old female (YOF) with asthma and coronary artery disease (CAD) who has undergone cardioversion for new-onset atrial fibrillation (afib) and has a persistent tachycardia despite initial treatment with 50mg of metoprolol every 6 hours?

From the Guidelines

I recommend titrating the metoprolol dose to 25-50mg twice daily (BID) for this 78-year-old female patient with asthma and CAD who was recently cardioverted from atrial fibrillation to normal sinus rhythm. The previous regimen of 50mg every 6 hours (200mg total daily dose) was likely excessive once the patient converted to normal sinus rhythm, as rate control requirements typically decrease after cardioversion 1. According to the 2023 ACC/AHA/ACCP/HRS guideline for the diagnosis and management of atrial fibrillation, the oral maintenance dose for metoprolol tartrate is 25-200 mg, twice daily 1. Start with 25-50mg BID (50-100mg total daily dose) and monitor heart rate and blood pressure closely, aiming for a resting heart rate of 60-80 bpm. If the patient develops bradycardia (HR < 60), hypotension (SBP < 100), or bronchospasm, consider further reducing the dose. Given her history of asthma, be vigilant for any respiratory symptoms, as beta-blockers can exacerbate bronchospasm in some patients 1. The goal of continued metoprolol therapy is to maintain sinus rhythm, provide cardioprotection for her CAD, and prevent recurrence of atrial fibrillation while minimizing adverse effects.

Some key points to consider when titrating the metoprolol dose include:

• Monitoring heart rate and blood pressure closely to avoid bradycardia or hypotension
• Being vigilant for respiratory symptoms, such as bronchospasm, in patients with asthma
• Adjusting the dose based on the patient's response to therapy and any adverse effects that may occur
• Considering alternative medications or dosing regimens if the patient is unable to tolerate metoprolol or if the desired therapeutic effect is not achieved.

It's also important to note that the patient's previous dose of 50mg every 6 hours may have been excessive, and reducing the dose to 25-50mg BID may help minimize adverse effects while still maintaining therapeutic efficacy 1.

From the FDA Drug Label

In patients who tolerate the full intravenous dose (15 mg), initiate metoprolol tartrate tablets, 50 mg every 6 hours, 15 minutes after the last intravenous dose and continued for 48 hours. Thereafter, the maintenance dosage is 100 mg orally twice daily Start patients who appear not to tolerate the full intravenous on metoprolol tartrate tablets either 25 mg or 50 mg every 6 hours (depending on the degree of intolerance) In general, use a low initial starting dose in elderly patients given their greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy. The patient was initially on 50mg metoprolol q 6 hrs, and since the patient is now in normal sinus rhythm after cardioversion, and considering the patient's age (78 YOF) and history of asthma and CAD, it would be prudent to titrate back on the metoprolol to the initial dose of 50 mg every 6 hours or consider a lower dose of 25 mg every 6 hours depending on the patient's tolerance, while closely monitoring the patient's heart rate and blood pressure 2.

• Key considerations:
  • Patient's age and comorbidities
  • Initial dose and tolerance
  • Need for close monitoring of heart rate and blood pressure
  • Potential for hepatic impairment in elderly patients, which may require low doses and cautious gradual dose titration.

From the Research

Atrial Fibrillation Treatment and Beta-Blocker Dosage

• The patient, a 78-year-old with a history of asthma and coronary artery disease (CAD), has been diagnosed with new onset atrial fibrillation (AF) and was initially on 50mg metoprolol every 6 hours, but still had a heart rate greater than 100bpm 3.
• After cardioversion, the patient is now in normal sinus rhythm, and the question arises as to what dose of metoprolol should be titrated back on.
• According to a study published in 2004, beta-blockers can prevent subacute recurrences of persistent atrial fibrillation, especially in patients with hypertension 4.
• The study suggests that beta-blockade is associated with a lower recurrence rate at 1 month, and that patients with hypertension maintain sinus rhythm better after cardioversion when treated with a beta-blocker.
• Another study published in 2009 recommends the use of oral beta blockers, verapamil, or diltiazem to slow a fast ventricular rate in AF, and suggests that amiodarone may be used in selected patients with symptomatic life-threatening AF refractory to other drugs 5.
• In terms of dosage, there is no specific guidance in the provided studies, but it is generally recommended to titrate beta-blockers to achieve a heart rate of less than 100bpm, while also considering the patient's underlying heart disease and other comorbidities.
• The patient's history of asthma should also be taken into account when adjusting the beta-blocker dosage, as beta-blockers can exacerbate asthma symptoms.
• Overall, the dosage of metoprolol should be titrated based on the patient's individual response and clinical status, with the goal of achieving a heart rate of less than 100bpm while minimizing adverse effects 3, 5, 4.