Antithyroid agents are hormone antagonists that inhibit thyroid hormone synthesis. Common antithyroid drugs include propylthiouracil, methimazole, and carbimazole. These drugs act by inhibiting the thyroid peroxidase enzyme, blocking the production of thyroid hormones. Antithyroid drugs are quickly absorbed orally and distributed throughout the body. They reduce thyroid hormone levels by 30-40% in treated patients but can cause side effects like hypothyroidism or agranulocytosis with long-term use.

1. ANTITHYROID AGENTS
DILSHANA FATHIMA
MSC. BIOCHEMISTRY

2. ANTITHYROID AGENTS
• Is a hormone antagonist acting upon thyroid hormones.
• Antithyroid medication generally are administered in
preperation for RAI ablation/surgery.
• The drugs commonly used are
propylthiouracil(PTU),methimazole,carbamizole etc.
• These drugs act by inhibiting the enzyme thyroid
peroxidase & in that way block the synthesis of thyroid
hormone.
• Reduce thyroid hormone production by inhibiting the
organic binding of iodine & coupling of iodotyrosines.

3. • A less common antithyroid agent is potassium
perchlorate.
• About 30-40% of patients treated with antithyroid
drug became euthyroid.
• A common problem with antithyroid drug is
undershooting/overshooting causing persistent
hyperthyroidism/hypothyroidism.
• A rare complication of antithyroid therapy is
agranulocytosis which calls for immediate
discontinuation of drug.
• All antithyroid drugs are quickly absorbed orally,
widely distributed in the body, enter milk & cross
placenta.
• Are metabolised in liver & excreted in urine
primarily as metabolites.

4. CLASSIFICATION
1. Inhibit hormone synthesis (antithyroid drugs)
Ex: PTU, methimazide, carbimazide
2. Inhibit iodine trapping (ionic inhibitors)
Ex: perchlorates, nitrates
3. Inhibit hormone release
Ex: iodine, iodides of Na & K
4. Destroy thyroid tissue
Ex: radioactive iodine

5. MECHANISM OF ACTION

6. • Iodides: blocks the release of stored thyroid
hormones from thyroid gland.
• β blockers: blocks the conversion of T4 to T3
• Thioamides: prevent the production of more T4 &
T3
 blocks the conversion of T4 to T3
outside the thyroid.

7. ADVANTAGES
• No surgical risk
• No scar/chances of injury to parathyroid or nearest
laryngeal nerve
• If treatment with antithyroid shoes side effects like
hypothyroidism then stoppage of treatment reverse
the action.
• Used for children as well as young adults.
• Control thyrotoxicosis in grave’s disease & toxic
nodular goiter.
• Can be used preoperatively

8. DISADVANTAGE
• Prolonged treatment is needed because stoppage of
treatment shows recurrence.
• Relapse rate is high
• High drug toxicity & side effects
• Not practicable in unintelligent pateint.