From Oral Levothyroxine Resistance To Intravenous Levothyroxine Hypersensitivity: A Challenging Primary Hypothyroidism Case
January 2026
in “
JCEM Case Reports
”
TLDR A woman with hypothyroidism developed an allergy to IV levothyroxine after being resistant to oral forms.
This case study presents a 51-year-old woman with primary hypothyroidism who developed resistance to oral levothyroxine (LT4) and hypersensitivity to intravenous (IV) LT4. Despite being euthyroid for 12 years on oral LT4, she became unresponsive to treatment, and alternative formulations and adjunctive therapies failed. An allergic reaction occurred with liquid LT4, and anaphylaxis developed during the first IV LT4 infusion. A desensitization protocol was implemented, which eventually allowed the patient to tolerate the treatment. This case highlights the potential for allergic reactions to IV LT4 in patients with previous allergies to other forms of the drug.