What is the recommended first-line treatment for hyperthyroidism according to the Philippine Clinical Practice Guidelines (CPG)?

First-Line Treatment for Hyperthyroidism in the Philippines

Methimazole is the recommended first-line antithyroid drug for most patients with hyperthyroidism, with the exception of the first trimester of pregnancy when propylthiouracil should be used. 1

Initial Management Approach

Symptomatic Control

• Start beta-blocker therapy immediately for symptomatic relief while determining definitive treatment, using atenolol 25-50 mg daily or propranolol 1
• Beta-blockers reduce symptoms until thioamide therapy takes effect 1

Diagnostic Confirmation Required

• Confirm hyperthyroidism biochemically with TSH and free T4 testing 1
• Add T3 measurement if symptomatic with minimal FT4 elevation 1
• Check TSH receptor antibodies if clinical features suggest Graves' disease (ophthalmopathy, diffuse goiter, or T3 toxicosis) 1

Definitive Antithyroid Drug Therapy

Methimazole as Preferred Agent

• Methimazole is the drug of choice because major side effects are less common, it can be used as single daily dose, it's less expensive and more available 2
• Starting dose is 10-30 mg as a single daily dose 2
• Use the lowest dose maintaining euthyroidism (titration method) for 12-18 months 3

Propylthiouracil Alternative

• Starting dose is 100-300 mg every 6 hours 2
• Reserved primarily for first trimester pregnancy due to methimazole's association with aplasia cutis and choanal/esophageal atresia 2

Treatment Duration and Monitoring

Standard Course

• Continue antithyroid drugs for 12-18 months as primary treatment 3
• Monitor thyroid function tests every 4-6 weeks during routine follow-up 1
• Maintain FT4 in high-normal range using lowest possible thioamide dose 1

Long-Term Considerations

• Hyperthyroidism relapses in approximately 50% of patients after 12-18 months of treatment 3, 4
• Long-term treatment with antithyroid drugs (5-10 years) is associated with fewer recurrences (15%) compared to short-term treatment 4
• For patients above 35 years of age, long-term treatment with low doses of methimazole (2.5-5 mg daily) may prevent relapse 5

Special Population: Pregnancy

Trimester-Specific Approach

• Propylthiouracil is the treatment of choice during or just prior to the first trimester of pregnancy 1
• Consider switching to methimazole for second and third trimesters given maternal hepatotoxicity risk with propylthiouracil 1
• Use lowest possible thioamide dose to maintain FT4 in high-normal range 1
• Monitor FT4 or free thyroxine index every 2-4 weeks during pregnancy 1
• Both drugs are safe during lactation despite presence in breast milk 2

Disease-Specific Considerations

Graves' Disease

• Graves' disease is persistent and requires definitive treatment 1
• Endocrine consultation is recommended for all suspected cases 1
• Antithyroid drugs, radioactive iodine, or surgery are the three definitive treatment options 1, 4

Thyroiditis-Induced Thyrotoxicosis

• Thyroiditis is self-limited and typically resolves within weeks with supportive care 1
• Treat with beta-blockers for symptomatic relief only 1
• High-dose corticosteroids are not routinely required 1
• Monitor thyroid function every 2-3 weeks to detect transition to hypothyroidism 1
• Initiate thyroid hormone replacement when TSH becomes elevated with low FT4 1

Common Pitfalls to Avoid

Side Effect Monitoring

• Side effects are relatively frequent but generally mild and transient 3
• Monitor for severe hyperthyroidism requiring dose adjustment or endocrine consultation if thyrotoxicosis persists beyond 6 weeks 1

Pregnancy Management Errors

• Do not use methimazole in first trimester due to teratogenic risk 2
• Do not continue propylthiouracil throughout entire pregnancy due to maternal hepatotoxicity risk 1