A rare case of levothyroxine overdose

Abstract

Background: Levothyroxine (LT4) can be life-threatening in overdose. There are limited cases reported, most of which are in children. Overdose, though rare, may lead to seizures, arrhythmias, and thyroid storm. Despite its potential for clinical catastrophe, it is underreported, and management guidelines are scarce. Herein, a case of LT4 overdose is reported.

Case: A 36-year-old African male with retroviral disease, mitral valve insufficiency, and Graves’ disease post-radioactive iodine therapy, ingested 10 000 μg of LT4 and 500 mg of warfarin in a self-harm attempt. He was stable on arrival, showing no signs of thyrotoxicosis or bleeding. Investigations revealed an FT4 > 100 pmol/l (reference range: 11.9–21.6 pmol/l) and an INR of 10.61. Vitamin K was administered for warfarin toxicity and LT4 was withheld. He was monitored in high care and received psychological therapy.

Discussion: LT4 overdose exceeding 5 000 μg can trigger thyrotoxicosis; however, endogenous compensatory mechanisms, such as increased reverse triiodothyronine (T3) production can delay toxicity. Overdose should be suspected when thyroxine (T4) is markedly elevated with a normal thyroid stimulating hormone (TSH). Management includes beta-blockers and glucocorticoids to inhibit peripheral T4-to-T3 conversion, with cholestyramine administered in severe cases.

Conclusion: This case highlights the critical need for close monitoring, even in the absence of acute symptoms, to prevent late onset fatalities.