Hepatotoxicity and cutaneous reactions after antithyroid drug administration

SummaryObjective Use of the antithyroid drugs (ATDs) thiamazole (MMI) and propylthiouracil (PTU) is associated with a high frequency of side effects. When patients experience side effects with one (the 1st) ATD, it is usually discontinued and another is administered (the 2nd ATD). We investigated side effects associated with the 1st and 2nd ATDs. Design and Patients Four hundred forty-nine patients with untreated Graves' disease (GD) were randomly assigned to three groups according to ATD type and/or dosage: 15 mg/day MMI, 30 mg/day MMI and 300 mg/day PTU. The type, frequency and onset of side effects were assessed. We also studied the side effects associated with the 2nd ATD after cessation of the 1st ATD. Measurements Cutaneous reactions, liver dysfunction and other side effects were examined every 2 weeks after starting ATD administration. Results The overall frequency of side effects in patients taking 15 mg/day MMI was low. The frequencies of cutaneous reactions in patients taking 30 mg/day MMI and hepatotoxicity in those taking 300 mg/day PTU were high. Hepatotoxicity developed later than cutaneous reactions with PTU. Hepatotoxicity developed earlier in the 30 mg/day MMI group than in the other two groups. The frequency of side effects did not differ between the 2nd and 1st ATDs. Hepatotoxicity occurred at a higher frequency in patients who were switched from MMI to PTU because of hepatotoxicity of the former. Conclusion Attention to the onset times of side effects and cross-reactivity of ATDs can lead to safer treatment of GD.