Thionamides

Carbimazole
Methimazole
Propylthiouracil

Indications

Hyperthyroidism.

Method of administration

40–60 mg od until euthyroid (4–8/52). 5–15 mg od maintenance. Discontinue after 18/12.

Mechanism

Carbimazole is metabolised to methimazole. Inhibits iodination of tyrosyl residues on thyroglobulin (organification) and coupling of iodotyrosyl residues. Propylthiouracil also inhibits T4 → T3 conversion.

Adverse effects

Rash, pruritis. Agranulocytosis (rare, but more common with propylthiouracil).