Thyroid Drugs

Thioamides

Drugs
- propylthiouracil (PTU)
- methimazole
Mechanism
- inhibit thyroid hormone synthesis by blocking peroxidase-catalyzed reactions
  - iodination of tyrosine residues of thyroglobulin
  - coupling of DIT and MIT
- propylthiouracil ↓ peripheral conversion of T₄ to T₃
Clinical use
- HYPERthyroidism
Toxicity
- skin rash
- agranulocytosis (rare)
- aplastic anemia
- hepatotoxicity (PTU)
  - PTU not used first line in non-pregnant adults and children for this reason
Pregnancy
- use PTU in the first trimester
methimazole crosses the placenta and enters breast milk (may be teratogenic)

Thyroid hormones