Antithyroid agents

Antithyroid agents

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 Inhibit hormone synthesis ( antithyroid drugs) Ex: PTU, methimazide , carbimazide Inhibit iodine trapping (ionic inhibitors) Ex: perchlorates , nitrates Inhibit hormone release Ex: iodine, iodides of Na & K 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 .