When to stop antithyroid drugs before giving radioactive iodine ablation therapy

When to stop antithyroid drugs before giving radioactive iodine ablation therapy:

- Carbimazole must be stopped 3 to 5 days before ablation therapy.

- Propylthiouracil must be stopped 2 weeks before ablation therapy.


Reference:

European Journal of Endocrinology (2002) 147 1–11

"On the basis, largely, of retrospective data, it appears that carbimazole (or ethimazole), if stopped 3–5 days before treatment, does not influence the outcome of 131I radioactive iodine) therapy. Simultaneous thyrostatic medication most probably reduces the efficacy of 131I, as does restarting it within 7 days. Propylthiouracil seems to have a more prolonged radioprotective effect than carbimazole.

"It only became similar to those treated with 131I alone if more than 15 days had elapsed between the last dose of antithyroid drug(propylthiouracil) and administration of 131I (47)."