How are antithyroid drugs initiated in a patient with hyperthyroidism?

It is prudent to get a baseline complete blood count, including white count with differential, and a liver profile including bilirubin and transaminases. A baseline absolute neutrophil count <500/mm3 or liver transaminases enzyme levels elevated more than five-fold the upper limit of normal are contraindications to initiating antithyroid drug therapy. Carbimazole and methimazole are started at a dose of 10–20 mg/day and has the advantage of being administered once daily. Propylthiouracil (PTU) has a shorter duration of action and is usually administered two or three times daily, starting with 50–150 mg three times daily. The 2016 American Thyroid Association guidelines suggests the following as a rough guide to initial MMI daily dosing: 5–10 mg if free T4 is 1–1.5 times the upper limit of normal; 10–20 mg for free T4 1.5–2 times the upper limit of normal; and 30–40 mg for free T4 2–3 times the upper limit of normal. These rough guidelines should be tailored to the individual patient, incorporating additional information on symptoms, gland size, and total T3 levels where relevant.