Allergic reactions to antithyroid drugs are associated with autoimmunity a retrospective case-control study

Thiamazole is the most used antithyroid drug for thyrotoxicosis in Basedow-Graves' (BG) (autoimmune) disease and in toxic multinodular goitre (TMG) (non-autoimmune). This study aims to find whether allergic reactions to thiamazole occur more frequently during the treatment of BG than of TMG.

Retrospective study, of 128 patients newly diagnosed and treated for thyrotoxicosis in the first 6 months of 2006, in the Endocrinology Department of "Elias" Hospital, Bucharest. Cases were all patients treated with thiamazole who developed allergic reactions. Controls were all patients treated with thiamazole without allergic reactions. Risk factor was considered to be the presence of BG.

Cases group consisted of 6 patients. All 6 started treatment with thiamazole for BG, and developed allergic reactions after 2-4 weeks of treatment. When thiamazole was withdrawn, allergic symptoms ceased under antihistamines and steroids. In order to control the thyrotoxicosis, antihistamines and oral steroids was administered, together with thiamazole in slow increasing doses. After about 4 weeks under this combination, a tolerance to thiamazole seems to appear. Control group consisted of 122 patients who started thiamazole: 66 for BG and 56 for TMG (without allergic reactions).

Allergy to thiamazole was significantly associated with the autoimmune BG, and not with TMG (p = 0.03, OR = 11.04). None of the patients with TMG developed allergic reactions to the drug. Tolerance to this drug may occur.