How should I treat an adult patient with hyperthyroidism?

Treatment of Hyperthyroidism

First-Line Treatment: Antithyroid Drugs

For most adult patients with hyperthyroidism due to Graves' disease or toxic nodular disease, initiate methimazole as the preferred antithyroid medication, except during the first trimester of pregnancy when propylthiouracil should be used. 1

Methimazole Dosing and Monitoring

• Start methimazole at an appropriate dose based on severity of hyperthyroidism (typically 10-30 mg daily) 1
• Monitor free T4 or free T3 every 2-4 weeks during initial treatment, targeting levels in the high-normal range using the lowest effective dose 1
• Do NOT use TSH to guide dose adjustments initially, as TSH may remain suppressed for months even after achieving euthyroidism 1
• Once free T4/T3 normalizes, continue methimazole for 12-18 months to attempt remission in Graves' disease 2

When to Use Propylthiouracil Instead

Switch to propylthiouracil only in these specific situations: 1, 3

• First trimester of pregnancy (due to lower risk of congenital malformations compared to methimazole) 3, 4
• Methimazole intolerance or allergy 1
• After the first trimester, switch back to methimazole for the remainder of pregnancy 1

Critical Safety Monitoring for Antithyroid Drugs

Instruct patients to report immediately and obtain CBC if they develop: 3, 4

• Sore throat or fever (agranulocytosis typically occurs within first 3 months) 1
• Skin eruptions, headache, or general malaise 3, 4
• Symptoms of hepatotoxicity (anorexia, pruritus, jaundice, right upper quadrant pain, dark urine) - especially with propylthiouracil 3
• Signs of vasculitis (new rash, hematuria, decreased urine output, dyspnea, hemoptysis) 3, 4

Symptomatic Management with Beta-Blockers

Start a beta-blocker immediately for symptomatic relief while awaiting thyroid hormone normalization: 1

• Atenolol 25-50 mg daily or propranolol are preferred agents 1
• Target heart rate <90 bpm if blood pressure tolerates 1
• Reduce beta-blocker dose once patient becomes euthyroid (hyperthyroidism increases beta-blocker clearance) 1, 4
• For patients with atrial fibrillation from hyperthyroidism, use beta-blockers for rate control 1

Definitive Treatment Options

Radioactive Iodine (I-131) Ablation

Radioactive iodine is the most widely used definitive treatment in the United States and should be considered after: 5, 6

• Failure of antithyroid drug therapy 2
• Patient preference for definitive cure 6
• Toxic multinodular goiter or toxic adenoma (where antithyroid drugs will not cure the condition) 2

Absolute contraindications to radioactive iodine: 1

• Pregnancy (must avoid pregnancy for 4 months after treatment) 1, 2
• Breastfeeding 1

Important consideration: Radioactive iodine may worsen Graves' ophthalmopathy; consider corticosteroid prophylaxis in at-risk patients 1, 2

Surgical Thyroidectomy

Consider surgery when: 2, 6

• Radioactive iodine is contraindicated or refused 2
• Large goiter causing compressive symptoms (dysphagia, orthopnea, voice changes) 2, 7
• Other treatments have failed 2

Special Clinical Scenarios

Destructive Thyroiditis

For thyroiditis-induced hyperthyroidism (including immune checkpoint inhibitor-induced): 1

• Do NOT use antithyroid drugs (thyroiditis is self-limited and involves hormone release, not overproduction) 1
• Provide symptomatic relief with beta-blockers during the hyperthyroid phase 1
• Monitor every 2 weeks with symptom evaluation and free T4 testing 1
• Initiate levothyroxine if patient becomes hypothyroid (low free T4/T3, even if TSH not yet elevated) 1

Subclinical Hyperthyroidism

Treat subclinical hyperthyroidism (TSH <0.1 mIU/L with normal free T4/T3) in: 1

• Patients over 60 years (3-fold increased risk of atrial fibrillation over 10 years) 1
• Those with cardiac disease, osteopenia, or osteoporosis risk 1
• Estrogen-deficient women (due to bone loss risk) 1

For TSH 0.1-0.45 mIU/L: routine treatment is not recommended due to insufficient evidence of adverse outcomes, except possibly in elderly patients with cardiovascular risk factors 1

Pregnancy Considerations

If pregnancy occurs or is planned during antithyroid therapy: 1, 4

• Use propylthiouracil during first trimester (lower risk of congenital malformations) 1, 4
• Switch to methimazole for second and third trimesters (lower maternal hepatotoxicity risk) 1, 4
• Maintain free T4 or free T3 in high-normal range using lowest possible dose 1
• Both medications are compatible with breastfeeding 1

Critical Drug Interactions

When patients become euthyroid on antithyroid drugs, reduce doses of: 1, 4

• Warfarin (increased anticoagulation effect; monitor PT/INR closely) 1, 4
• Beta-blockers (decreased clearance when euthyroid) 1, 4
• Digoxin (increased serum levels when euthyroid) 4
• Theophylline (decreased clearance when euthyroid) 1, 4

Common Pitfalls to Avoid

• Never reduce methimazole based solely on suppressed TSH while free T4 remains elevated - this leads to inadequate treatment and recurrent hyperthyroidism 1
• Never attempt cardioversion in thyrotoxic atrial fibrillation without first achieving euthyroid state - antiarrhythmics and cardioversion are generally unsuccessful while thyrotoxicosis persists 1
• Never use antithyroid drugs for thyroiditis - the condition is self-limited and involves hormone release, not synthesis 1