DESENSITIZATION TO PROPYLTHIOURACIL WITH SUBSEQUENT LONG-TERM THERAPY TOLERANCE IN A PREGNANT PATIENT

Abstract

<h3>Introduction</h3> Thionamides are first line treatment for hyperthyroidism due to Graves' disease in pregnancy. Propylthiouracil (PTU) is preferred to methimazole in the first trimester, given risk of significant teratogenic effects with methimazole. Hypersensitivity reactions such as angioedema and anaphylaxis to thionamides have been reported, and there is concern for cross-reactivity between methimazole and PTU. A lack of data exists regarding the safety of graded challenge or desensitization to thionamides during pregnancy. <h3>Case Description</h3> A 33-year-old female with history of Graves' disease and prior urticaria and angioedema with use of methimazole presented to allergy clinic while 9 weeks pregnant with symptoms of tachycardia, jitteriness, dyspnea, and weight loss. She was diagnosed with thyroid storm and endocrinology recommended PTU initiation. Given her previous reaction to methimazole with potential risk of cross-reactivity as well as her urgent need for treatment during pregnancy, an outpatient graded challenge was deferred and she was admitted to the intensive care unit for a 7-step desensitization to PTU. She tolerated this during her first trimester of pregnancy without adverse events and was able to be continued on outpatient PTU for the remainder of her pregnancy with subsequent delivery of a healthy baby. <h3>Discussion</h3> Currently, 2016 American Thyroid Association Guidelines for Hyperthyroidism recommend against using methimazole or PTU in those who have had a serious side effect from the other agent due to concern of cross-reactivity, although this is not well quantified. This case reinforces that desensitization to thionamides can be safely performed during pregnancy in the setting of prior reactions.