Efficacy and safety of propylthiouracil protocols: high-dose monotherapy vs combination of low-dose with iodine

Background Propylthiouracil (PTU) use has decreased due to adverse events (AEs), but it is still needed for patients who cannot tolerate thiamazole. Objective To compare the efficacy and safety of the PTU protocol between high-dose monotherapy and low-dose combination therapy with potassium iodide (KI). Methods This is a retrospective observational study including patients who were newly diagnosed with Graves disease (GD) and received PTU as initial therapy between January 2005 and October 2024. Patients who received an initial dose of 300 mg (high-dose group) and those who received 150 mg of PTU combined with 50 mg of KI (low-dose group) were included. The propensity-score matching method was employed to adjust for confounders. Results A total of 1171 patients (high-dose: low-dose = 1133: 38, all female) with a median age of 32 (interquartile range [IQR]: 28-36) years were included. Median levels of free-thyroxine (FT4) and thyroid-stimulating hormone receptor antibody were 4.97 (IQR: 3.67-7.31) ng/dL, 12.4 (IQR: 6.4-26.8) IU/L. Adverse events occurred in 294 patients (high-dose: low-dose = 289:5). Free-thyroxine levels were significantly lower at Week 2 in the low-dose group than in the high-dose group (P = .014), but the difference disappeared afterwards. The prevalence of inadequate efficacy with the initial dose was significantly higher in the low-dose group (12.8% vs 35.5%, P = .002). Conclusion Despite a lower rate of efficacy from the initial dose, the low-dose protocol was effective in controlling hyperthyroidism with up-titration in young women with GD, with the potential for fewer AEs.