What is an appropriate equivalent dose of propranolol for a patient taking atenolol 75 mg once daily?

Propranolol Equivalent Dose for Atenolol 75 mg

For a patient taking atenolol 75 mg once daily, switch to propranolol 120–160 mg daily, divided into two doses (60–80 mg twice daily) of immediate-release formulation, or 120–160 mg once daily of long-acting propranolol. 1

Dose Conversion Rationale

The 2014 AHA/ACC/HRS atrial fibrillation guideline provides standard maintenance dosing for both agents in cardiovascular rate control: atenolol 25–100 mg once daily versus propranolol 10–40 mg three to four times daily (total 30–160 mg/day). 1 Since atenolol 75 mg falls in the mid-to-upper therapeutic range, an equivalent propranolol dose of 120–160 mg daily is appropriate. 1

Key Pharmacologic Differences

• Milligram-for-milligram, atenolol and propranolol are not equivalent. Research demonstrates that atenolol 100 mg once daily produces cardiovascular beta-blockade roughly equivalent to metoprolol 100 mg twice daily or 300 mg once daily, indicating atenolol has greater per-milligram potency than many other beta-blockers. 2

• Propranolol requires divided dosing because its immediate-release half-life is only 3–6 hours, necessitating 3–4 times daily administration for continuous blockade. 34 In contrast, atenolol's 24-hour half-life permits true once-daily dosing. 5

• Long-acting propranolol formulations (half-life 8–20 hours) allow once-daily dosing at 80–160 mg, making them more comparable to atenolol's convenience. 34

Recommended Conversion Protocol

Option 1: Immediate-Release Propranolol

• Start propranolol 60 mg twice daily (total 120 mg/day) and titrate to 80 mg twice daily (160 mg/day) if heart rate remains above target (typically <75–90 bpm at rest). 6
• Administer doses with or after meals to reduce hypoglycemia risk. 3
• Space doses no more than 8 hours apart to maintain steady beta-blockade. 6

Option 2: Long-Acting Propranolol

• Start propranolol LA 120 mg once daily, titrating to 160 mg once daily as needed for rate or blood pressure control. 36
• This formulation provides more stable plasma levels and may improve compliance compared to multiple daily doses. 4

Mandatory Pre-Conversion Assessment

Before switching from atenolol to propranolol, screen for absolute contraindications that may not have been relevant with the cardioselective agent atenolol: 13

• Asthma or obstructive airway disease (propranolol's non-selective β2-blockade can precipitate life-threatening bronchospasm, whereas atenolol's cardioselectivity confers relative safety). 3
• Second- or third-degree AV block without a pacemaker. 1
• Decompensated heart failure or cardiogenic shock. 1
• Severe hypotension (systolic BP <90 mm Hg). 3

Critical Safety Difference: Respiratory Risk

Propranolol blocks both β1 and β2 receptors; β2 antagonism causes bronchoconstriction, making it absolutely contraindicated in any patient with asthma or COPD. 3 Atenolol's β1-selectivity means patients who tolerated atenolol may still be unsuitable for propranolol if they have even mild reactive airway disease. 3

Post-Conversion Monitoring

• Measure heart rate and blood pressure 1–2 hours after the first propranolol dose to detect excessive beta-blockade (heart rate <50 bpm, systolic BP <90 mm Hg, dizziness, or marked fatigue). 6

• Reassess at 4–7 days: if resting heart rate remains >75–90 bpm, increase the dose incrementally. 6

• In stable patients on maintenance therapy, routine vital sign checks between appointments are not required. 3

Drug Interaction Alert

Avoid combining propranolol with non-dihydropyridine calcium-channel blockers (diltiazem, verapamil), as this markedly increases the risk of severe bradycardia and heart block—a risk that is lower with atenolol. 13

Special Population Considerations

• Diabetic patients: Propranolol masks adrenergic warning signs of hypoglycemia (tremor, tachycardia) more than atenolol does; counsel patients to monitor glucose more frequently and rely on non-adrenergic cues (hunger, confusion, sweating). 36

• Elderly patients: May require lower propranolol doses (start at 80 mg/day total) due to altered pharmacokinetics. 6

• Renal impairment: Atenolol requires dose reduction in severe renal dysfunction, whereas propranolol (hepatically metabolized) does not; however, if the patient was stable on atenolol 75 mg, renal function is likely adequate. 3

Discontinuation Guidance

Never abruptly stop propranolol after chronic use—taper gradually over 1–3 weeks to prevent rebound hypertension, tachycardia, or angina. 36 This risk is present with all beta-blockers but is particularly important to emphasize when transitioning from atenolol, as patients may not have been counseled about tapering if they were on a stable once-daily regimen.

Common Pitfall: Underdosing

Clinicians often underestimate the propranolol dose needed to match atenolol's effect. A 1:1 milligram conversion is incorrect; propranolol 75 mg daily would provide substantially less beta-blockade than atenolol 75 mg. 2 The 120–160 mg daily propranolol range is necessary to achieve equivalent cardiovascular effects. 16