No rash decisions – a probable case of hypersensitivity to inert ingredients.

Abstract

Objective: To describe a probable case of hypersensitivity to levothyroxine tablet. Clinical features: A 12-year-old Caucasian female presented with a two-month history of pain and fatigue with no significant past medical history. Baseline bloods including thyroid function tests (TFT) identified hypothyroidism with antithyroglobulin antibody in normal range and antithyroid peroxidase markedly elevated (greater than 1300 U/mL). The patient was diagnosed with Hashimoto’s thyroiditis and commenced on levothyroxine tablets 50 microgram daily. On day 5 of treatment, the patient developed a rash including “itchy red spots” across the chin and forehead. Literature review: Hypersensitivity to levothyroxine has not been documented, however, inactive ingredients in tablet formulations may cause hypersensitivity reactions, including urticaria, pruritus, rash, flushing, angioedema, gastrointestinal symptoms, fever, arthralgia, serum sickness, and wheezing. Case reports in adults have been published however to the best of our knowledge, no cases in children have been reported. Pharmacist interventions, case progress and outcomes: Levothyroxine administration was ceased. Consultation with the paediatric endocrinologist occurred who confirmed that allergy to levothyroxine itself would be unlikely. The question of how to manage ongoing thyroid hormone supplementation was posed to the paediatric pharmacist. A literature search concluded the reaction was likely due to tablet excipients, or was incidental. Review of available levothyroxine tablet formulations including excipient lists occurred, with trial of an alternate tablet brand being recommended. The patient tolerated the new brand of levothyroxine with no rash reported after 7-days of treatment. Ongoing paediatrician review and TFT monitoring to assess response will occur. Discussion: Hypersensitivity reactions to levothyroxine including urticaria, pruritis and rash are most likely due to inactive tablet ingredients. Common allergens including food components and colouring agents should be considered. Trial of an alternate brand with differing excipients should occur prior to consideration of the need for alternate agents or allergy testing.