Endocrine Abstracts

Introduction: Levothyroxine, the standard therapy for hypothyroidism, is usually well tolerated and very few cases of true allergy to levothyroxine have been reported to date. Here we report two cases of rare occurrence of levothyroxine allergy.

Case 1: A 56-year-old woman with no previous history of allergies started levothyroxine post-thyroidectomy for Graves’ disease. She developed facial flushing and urticarial rash within 15 minutes of the first-dose of levothyroxine 1 mg. She was treated with steroids and antihistamine. She developed similar symptoms on the next dose, and tryptase levels confirmed allergy. She was trialed on levothyroxine elixir to exclude excipient-related allergy, but symptoms recurred despite concurrent antihistamine and steroid. Later, she tolerated liothyronine, with no adverse symptoms. Desensitization to levothyroxine was undertaken. A rash appeared at higher doses but settled within 24hours. She currently tolerates 1 mg daily. Given her lack of other allergies and as excipient-related allergy is common in other drugs, we are now investigating an allergy to dextrothyroxine.

Case 2: We report a 56-year-old man with autoimmune hypothyroidism. TSH was 7.1 mU/l when he presented with tiredness, which improved with levothyroxine. Over the last 18 months, his levothyroxine requirement increased to 1 mg daily, with TSH frequently >1 mU/l. Compliance issue and malabsorption disorders were excluded. He gained weight, and developed type 2 diabetes. He developed bilateral foot swelling, and cracking of his feet with facial rash and swelling. He trialed several oral forms (liquid and tablets) of levothyroxine. He was then trialed on Armour Thyroid 1 mg three times daily without adverse effect. His thyroid function improved and he lost weight leading to diabetes remission. Later, due to supply issues he was changed to liothyronine 1 mg twice daily and levothyroxine 1 mg daily with stable thyroid function.

Conclusions: Hypersensitivity to levothyroxine is rare and most patient with reaction to levothyroxine tolerated to alternative thyroxine preparation. It is hypothesized that levothyroxine allergy is likely due to the excipients or fillers rather than the thyroid hormone itself.