first-line antithyroid drug
The preferred thionamide for almost all cases of hyperthyroidism (except 1st trimester pregnancy and thyroid storm) due to its longer half-life, once-daily dosing, and better safety profile compared to PTU.
- Mechanism: Inhibits Thyroid Peroxidase (TPO), blocking the oxidation of iodide and organification of iodine (synthesis of T4/T3). Does not block peripheral conversion.
- Dosing:
- Start: 10–40 mg PO daily (depending on fT4 levels).
- Maintenance: 5–10 mg daily.
- PK: Half-life: 6–9 hours (allows OD dosing). Concentrates in the thyroid.
indications
- Graves’ Disease: To induce remission or prep for definitive therapy.
- toxic multinodular goitre / Adenoma: To normalize levels before RAI/Surgery.
- Amiodarone-Induced Thyrotoxicosis (Type 1): High doses (40–60 mg) often needed.
adverse effects
- Minor: Rash, arthralgia, GI upset (~5%).
- Major:
- Agranulocytosis (0.2–0.5%): Idiosyncratic. Patients must seek care immediately for fever/sore throat.
- Hepatotoxicity: Cholestatic jaundice (less severe than PTU).
- Teratogenicity: Aplasia cutis, choanal atresia, tracheoesophageal fistula (avoid in T1 Pregnancy).
related pages: Propylthiouracil, Hyperthyroidism, Graves’ Disease, Hyperthyroidism in Pregnancy