Does carbimazole have an effect on I-131 therapy in Graves disease?

431 Objectives The influence of carbimazole on radioiodine (RAI) therapy is controversial, with reports of equal or even better response, or radioresistance after carbimazole pretreatment. Methods We investigated the 3 months outcome post RAI therapy of patients on or not on carbimazole prior to RAI. The dose, duration and period of withdrawal of carbimazole were noted. Baseline T4, T3 and TSH were compared with those at 3 months. Results Graves’ disease patients (1062) were included, with 487 patients pretreated and 575 carbimazole naive. There was no statistically significant difference between the 2 groups regarding the patients’ gender, weight and age. Of the carbimazole group, 98.9% patients came for follow-up and 98.3% of those not on the drug. Hypothyroidism, euthyroidism and hyperthyroidism were found in 55.8%, 28.0%, and 16.2% of the carbimazole group respectively, and 72.4%, 11.5% and 16.1% respectively in the group not on carbimazole.Comparison of the mean free T4 and T3 at baseline and at 3 months for the two groups showed a statistically better response in the group not on carbimazole (p Conclusions Carbimazole given prior to RAI therapy does negatively influence the RAI therapy effect 3 months after RAI. In this study the other factors significantly affecting RAI therapy are dose of I-131, severity of hyperthyroidism reflected in the baseline thyroid function tests and uptake values.