The effect of pretreatment with propylthiouracil or methimazole on subsequent ¹³¹I therapy in Graves’disease

Objectives: Anti-thytoid drug might affect thyroidal uptake of ¹³¹I. In this study the effects of propylthiouracil (PTU) and methimazole( MMI ) pretreatment on ¹³¹I therapy in Graves’ disease were evaluated.

Methods: Fifty-six cases of Graves' disease without PTU were enrolled as control(N),44 pretreated with PTU were randomized to groups PA and PB, and 73 pretreated with MMI were randomized to groups MA and MB. Patients in groups N, PA and MA were given ¹³¹I at dosage of 2.96MBq per gram of thyroid tissue. Patients in group PB and MB had 30% increased dosage. Four months after the therapy, the therapeutic effect in five groups was evaluated and the cure rates and the hypothyroidism were compared.Results The therapeutic effective rate of the 173 patients with ¹³¹I was 82.66%. The cure rate in group N was 91.07%,which was markedly higher than that in the group PA (50%,P<0.01),The cure rate in group PB,MA and MB was 86.36%,86.67% and 83.72%, similar to group N (91.07%).The rate was obviously different compared with PA (P < 0.01). Conclusion PTU might have negative effect on the effectiveness of radioiodine therapy in Graves' disease, but its effect could be overcome by increase of radioactivity dose to the patients, but the MMI not have the direct effect.