Treatment of Hyperthyroidism
Methimazole is the first-line antithyroid drug for hyperthyroidism due to superior efficacy and safety, with propylthiouracil reserved only for patients intolerant to methimazole or during the first trimester of pregnancy. 1, 2
Initial Treatment Approach
First-Line Medical Therapy
- Methimazole is the preferred antithyroid drug with starting doses of 10-30 mg once daily, offering superior efficacy, fewer severe side effects, and convenient single-daily dosing compared to propylthiouracil 1, 3
- Methimazole achieves euthyroidism significantly faster than propylthiouracil, with 77% of patients reaching normal thyroid levels versus only 19% with propylthiouracil at equivalent treatment duration 4
When to Use Propylthiouracil
- Propylthiouracil should only be used in two specific situations: patients intolerant to methimazole, or during the first trimester of pregnancy 1, 2
- The FDA restricts propylthiouracil use due to risk of severe liver failure, liver transplantation, or death, particularly dangerous in pregnant women and their infants 2
- Starting dose is 100-300 mg every 6-8 hours (not once daily due to shorter half-life) 5
Immediate Symptom Control
Beta-Blocker Therapy
- Initiate beta-blockers immediately for symptomatic relief while awaiting thyroid hormone normalization, particularly for tachycardia, tremor, and anxiety 1
- Atenolol 25-50 mg daily or propranolol are effective options 1
- Reduce beta-blocker dose once euthyroid state is achieved to avoid excessive bradycardia 1
Definitive Treatment Options
Radioactive Iodine (I-131)
- Radioactive iodine is increasingly used as first-line definitive therapy, particularly for toxic nodular goiter where it is the treatment of choice 1, 6
- Absolute contraindications: pregnancy and breastfeeding 1
- Pregnancy must be avoided for 4 months following administration 1, 6
- Stop antithyroid drugs at least one week before radioiodine to reduce treatment failure risk 7
- May worsen Graves' ophthalmopathy; consider corticosteroid prophylaxis in at-risk patients 1, 6
Surgical Thyroidectomy
- Reserved for specific situations: large goiters causing compressive symptoms, patient refusal of radioiodine, or when rapid definitive treatment is needed 6
- Should be performed as near-total or total thyroidectomy 7
Treatment Duration and Monitoring Strategy
Monitoring Schedule
- Check free T4 or free T3 every 2-4 weeks during initial treatment to maintain levels in the high-normal range using the lowest effective dose 1
- For Graves' disease, typical treatment duration is 12-18 months 1, 6
- If TSH-receptor antibodies remain above 10 mU/L after 6 months of treatment, remission is unlikely and definitive therapy with radioiodine or surgery should be recommended 7
Dose Adjustments
- Keep methimazole starting dose at 15-20 mg/day or less to minimize risk of dose-dependent agranulocytosis 7
Critical Safety Monitoring
Life-Threatening Adverse Effects (First 3 Months)
Agranulocytosis:
- Occurs typically within first 3 months of thioamide therapy 1
- Immediately discontinue drug and check CBC if patient develops fever, chills, or sore throat 1, 2
Hepatotoxicity (Especially with Propylthiouracil):
- Stop drug immediately if patient develops: fever, nausea, vomiting, right upper quadrant pain, dark urine, pale stools, or jaundice 1, 2
- Can progress to liver failure requiring transplantation or causing death 2
Vasculitis:
- Life-threatening complication that can affect skin, kidneys, or lungs 1, 2
- Watch for: skin rash or color changes, hematuria, foamy urine, decreased urine output, shortness of breath, or hemoptysis 2
Important Drug Interactions
- Warfarin requires dose reduction due to increased anticoagulation effect when taking antithyroid drugs 1
- Theophylline clearance decreases when patient becomes euthyroid, requiring dose adjustment 1, 2
- Digoxin levels may be affected 2
Special Populations
Destructive Thyroiditis
- Do not use antithyroid drugs as this condition is self-limited 1
- Treat symptomatically with beta-blockers only 1