Propylthiouracil is administered orally. The total daily dosage is usually given in 3 equal doses at approximately 8 hour intervals. The initial dose in adults is 300 mg daily. In patients with severe hyperthyroidism, very large goiters, or both, the initial dose may be increased to 400 mg daily; an occasional patient will require 600 to 900 mg daily initially. The usual maintenance dose is 100 to 150 mg daily.

Thyroid peroxidase activity was measured by monitoring the formation of resorufin from the oxidation of Amplex Red.Assay mixtures (100 uL) contained 50 mM sodium phosphate buffer, pH 7.4, 150 mM NaCl, 2 uM H2O2, 30 uM Amplex Red, 1 mM diethylenetriaminepentaacetic acid, and 2% DMSO. The reactions were initiated by the addition of TPO. Reaction mixtures to determine the background reaction rate consisted of all assay components and 4 uL of 500 unit/mL bovine catalase in 50 mM potassium phosphate buffer, pH 7.0. The background rate was subtracted from each reaction progress curve. IC50 for propylthiouracil was 3.38 uM.