Propranolol Dosing for Palpitations and Tachycardia in Thyrotoxicosis
For acute management of palpitations and tachycardia in the ER setting with elevated FT3, administer propranolol 1 mg IV over 1 minute, which can be repeated every 2 minutes up to a maximum of 3 doses (total 3 mg), targeting heart rate control below 100-110 bpm. 1
Intravenous Administration Protocol
- Initial bolus: Give 1 mg propranolol IV push over 1 minute 1
- Repeat dosing: May repeat 1 mg every 2 minutes as needed 1
- Maximum acute dose: Up to 3 total doses (3 mg total) 1
- Monitor continuously: Blood pressure and heart rate between each dose to detect hypotension or excessive bradycardia 1
Rationale for Propranolol in Thyrotoxicosis
Propranolol is the preferred beta-blocker in hyperthyroid states because it provides dual benefits beyond simple beta-blockade. At therapeutic doses, propranolol reduces serum T3 levels by inhibiting peripheral conversion of T4 to T3, while simultaneously increasing reverse T3 (rT3) levels. 2 This metabolic effect becomes clinically significant at propranolol plasma concentrations above 150 ng/ml, which corresponds to doses of 240-320 mg daily in oral therapy. 2
Transition to Oral Therapy
Once acute rate control is achieved in the ER, transition to oral propranolol:
- Standard oral dose: 10-40 mg orally 3-4 times daily 1
- For hyperthyroidism specifically: Start with 40 mg every 6-8 hours (160 mg daily), with potential escalation to 240-320 mg daily if heart rate remains above 75 bpm after 4-7 days 2
- Therapeutic plasma level: Target propranolol levels of 150-500 ng/ml for optimal antiarrhythmic and anti-thyroid effects 3, 2
Critical Monitoring Parameters
During IV administration:
- Heart rate every 1-2 minutes during bolus administration 1
- Blood pressure continuously to detect hypotension 1
- ECG monitoring for bradycardia or heart block 1
After transition to oral therapy:
- Resting heart rate (target <75-80 bpm) 2
- Free T3 levels should decrease by approximately 51% within days of adequate beta-blockade 4
- Clinical symptoms: tremor, sweating, palpitations 2
Absolute Contraindications
Propranolol must be avoided in patients with: 1
- Decompensated heart failure or cardiogenic shock
- Severe asthma or active bronchospasm
- High-degree AV block (second or third degree) without pacemaker
- Severe bradycardia (<50 bpm)
Alternative Beta-Blocker Options
If propranolol is contraindicated or not tolerated, consider cardioselective beta-blockers, though they lack the T3-lowering effect:
- Metoprolol IV: 2.5-5 mg bolus over 2 minutes, up to 3 doses (maximum 15 mg) 1
- Esmolol infusion: 500 mcg/kg loading dose over 1 minute, followed by 50-300 mcg/kg/min infusion for ultra-short-acting control 1
However, metoprolol produces only minimal reduction in T3 levels even at high doses (300-400 mg daily), making it less ideal for thyrotoxicosis. 2
Common Pitfalls to Avoid
- Underdosing in thyrotoxicosis: Hyperthyroid patients often require higher propranolol doses (240-320 mg daily orally) than typical cardiac indications due to increased metabolic clearance and the need for T3 suppression 2
- Abrupt discontinuation: Never stop propranolol suddenly in thyrotoxic patients, as this causes rebound increases in free T3 (up to 51-74% elevation) within 2-6 days, potentially precipitating thyroid storm 4
- Excessive bradycardia: If heart rate drops below 50 bpm or symptomatic hypotension develops, hold further doses and consider atropine 0.5 mg IV 1
Continuous Infusion for Refractory Cases
For patients requiring prolonged rate control who cannot take oral medications: