Hypo & Hyperthyroidism

Dr. SalmanPharmacology LMDC

Hypothyroidism

• It is treated with the hormone itself!– Thyroxine, or 3,5,3',5'-tetraiodothyronine

(often abbreviated as T4)

– Injected T4

Antihyperthyroid Drugs

The synthesis of thyroid hormone and action and effects of

antithyroid agents

Inhibited by propranolol, and propylthioiracil

Conversion of T4 to T3 via 5’ deiodinase in peripheral tissues

6

Inhibited by high doses of iodide

Proteolytic release of T3 and T4 from thyroglobulin

5

4

3

2

1

Inhibited by thioamidesCoupling of MIT and MIT to form T3 and T4

Inhibited by thioamidesIodination of tyrosyl residues on thyroglobulin from MIT and DIT

Inhibited by thioamidesOxidation of iodide by peroxidases

Basis for selective cell destruction of 131I

Active accumulation of iodide into the gland

Effects of antithyroid agents

Thyroid hormone synthesis and action

Thioamides: Propylthiouracil and Methimazole

• Use in uncomplicated hyperthyroid conditions; • High-dose propylthiouracil inhibits 5' deiodinase• Common maculopapular rash

• Less common ↓ prothrombin, hypersensitivity, and immune-based arthralgia,

• jaundice, lupus, and vasculitis• Both drugs cross the placental barrier, but PTU

is safer in pregnancy because it is• extensively protein bound

Iodide

• KI+ iodine (Lugol's solution) possible use in thyrotoxicosis: used preoperatively, →↓ gland size, fragility, and vascularity

• No long-term use because thyroid gland "escapes" from effects after 10-14 days