Methimazole and propylthiouracil (PTU) are first-line therapies for hyperthyroidism, but rare adverse reactions such as hypersensitivity and agranulocytosis can limit their use. In such cases, alternative treatments are often unavailable in resource-limited settings, posing a significant challenge in urgent hyperthyroidism management.

A 36-year-old asthmatic female was diagnosed with hyperthyroidism in June 2025. Methimazole 20 mg twice daily was initiated but discontinued after three days due to a neck rash, which resolved with cetirizine. She was shifted to PTU 100 mg TID and propranolol. After two weeks, she presented with fever, chills, and sore throat. Laboratory workup showed agranulocytosis (ANC 742/μL, neutrophils 15%, WBC 4.95 ×10⁹/L). FT4 remained elevated at 4.19 ng/dL. She was admitted and treated with filgrastim, piperacillin-tazobactam, lithium 300 mg BID, and digoxin 0.25 mg OD. Clinical and hematologic recovery was noted, and she was discharged.

Two months later, she remained thyrotoxic (FT4 6.99 ng/dL, TSH 0.0002), prompting readmission due to risk of thyroid storm. ALT was elevated (86 U/L), with eosinophilia (7%) and low-normal neutrophils (44%). Despite continued lithium, dexamethasone, and digoxin, thyroid hormone levels remained uncontrolled. With potassium iodide, cholestyramine, and plasmapheresis unavailable, a cautious inpatient trial of carbimazole (5 mg BID) was initiated despite prior methimazole hypersensitivity. After four days, FT4 improved to 2.91 ng/dL, and no recurrence of hypersensitivity occurred. The patient was discharged on carbimazole, with plans for radioactive iodine therapy once euthyroid.

This case highlights the clinical complexity of managing severe hyperthyroidism with dual ATD intolerance. Agranulocytosis requires immediate withdrawal of PTU and supportive therapy. Although carbimazole is a methimazole prodrug, it may be cautiously reintroduced in select patients with non-anaphylactic reactions, under close supervision. Lithium and corticosteroids serve as valuable temporizing agents but may be insufficient alone. Timely recognition of adverse effects, individualized management, and early planning for definitive therapy are critical, especially in settings with limited access to advanced therapies.