Treatment of Thyrotoxicosis (Thyroid Poisoning)
Beta-blockers are the immediate first-line treatment for symptomatic thyrotoxicosis to control cardiovascular manifestations, followed by definitive therapy with antithyroid drugs (methimazole), radioactive iodine, or surgery depending on the underlying cause. 1
Immediate Symptomatic Management
Beta-Blocker Therapy (First Priority)
Propranolol is the preferred beta-blocker because it not only controls heart rate and tremor but also inhibits peripheral conversion of T4 to the more biologically active T3. 1
- Standard dosing: Propranolol 40 mg orally every 6 hours for symptomatic control 1, 2, 3
- Intravenous beta-blockers (such as esmolol) are particularly useful when hemodynamic instability is a concern or in thyroid storm 1
- High doses may be required in severe cases or thyroid storm due to increased adrenergic tone 1
Alternative beta-blockers include nadolol 80 mg once daily, which offers the advantage of once-daily dosing and better patient compliance, with similar efficacy to propranolol. 2 Nadolol pharmacokinetics are not appreciably altered by thyrotoxicosis, unlike propranolol which has significantly lower serum levels in the thyrotoxic state. 2
When Beta-Blockers Cannot Be Used
Non-dihydropyridine calcium channel antagonists (diltiazem or verapamil) are recommended alternatives when beta-blockers are contraindicated. 1 However, digoxin is less effective when adrenergic tone is high, making it a poor choice in acute thyrotoxicosis. 1
Definitive Treatment Based on Etiology
For Graves Disease and Toxic Multinodular Goiter
Methimazole is the preferred antithyroid drug for definitive medical management. 4, 5
- Methimazole inhibits synthesis of new thyroid hormones but does not inactivate existing circulating hormone 4
- It typically induces remission in Graves disease and controls hyperthyroidism in multinodular goiter 5
- Important limitation: The drug requires weeks to months to normalize thyroid function because it doesn't affect stored or circulating hormone 4
Radioactive iodine resolves hyperthyroidism in more than 90% of patients with Graves disease and toxic multinodular goiter, though hypothyroidism develops in most patients within 1 year after treatment. 5
Thyroidectomy is the treatment of choice for patients with compressive symptoms from an obstructive goiter. 5
Preparation for Surgery
Propranolol alone can be used as preparation for subtotal thyroidectomy, with a mean preoperative period of 17 days (range 4-60 days) at 40 mg every 6 hours, continued for 7 days postoperatively. 3 This approach has advantages over conventional preparation with carbimazole and potassium iodide, including reduced preparation time, more flexible timing of operation, and reduced operative blood loss (mean 160 ml). 3
Thyroid Storm Management
For impending or established thyroid storm (Burch-Wartofsky Point Scale score ≥25):
- Mandatory hospitalization with endocrine consultation 6
- Aggressive beta-blocker therapy to manage cardiovascular symptoms 6
- Close monitoring for progression 6
For scores <25, manage as severe thyrotoxicosis with beta-blockers and supportive care, with close monitoring for deterioration. 6
Resistant Thyrotoxicosis
When conventional therapy fails, consider adjunctive treatment:
- High-dose corticosteroids (prednisolone 1 mg/kg/day) to reduce T4 levels 7
- Lithium (400 mg twice daily) as an additional agent to prepare patients for radioactive iodine 7
- These agents play an important role in preparing patients with resistant disease for definitive treatment with radioactive iodine or surgery 7
Critical Pitfalls to Avoid
Never attempt cardioversion or antiarrhythmic drugs for atrial fibrillation complicating thyrotoxicosis until thyroid function is normalized, as these interventions are generally unsuccessful while thyrotoxicosis persists. 1
Do not delay beta-blocker therapy while waiting for antithyroid drugs to take effect—beta-blockers provide immediate symptomatic relief while definitive therapy requires weeks to months. 1, 4
Monitor for drug interactions when patients become euthyroid: beta-blocker clearance may increase, digitalis levels may rise, and theophylline clearance may decrease, all requiring dose adjustments. 4
Anticoagulation is recommended based on stroke risk factors in patients with thyrotoxicosis-induced atrial fibrillation, with standard precautions if AF persists longer than 48 hours. 1