Intentional co-ingestion of levothyroxine and insulin in a teenager

To report a case of polydrug ingestion involving levothyroxine and insulin in an adolescent, demonstrating potential protective effects of insulin co-ingestion against symptomatic thyrotoxicosis.

A 14-year-old female with type 1 diabetes and Hashimoto thyroiditis presented following intentional ingestion of 6.75 milligrams levothyroxine, 60 units insulin aspart, and 80 units insulin degludec. Laboratory studies revealed severe biochemical thyrotoxicosis with free thyroxine greater than 7.77 nanograms per deciliter and total triiodothyronine 220.5 nanograms per deciliter. She required glucose infusion at 2.3 to 3.7 milligrams per kilogram per minute to maintain normoglycemia, with hypoglycemic episodes lasting up to 17 h post-ingestion. Throughout her 12-day admission, she maintained normal vital signs with no clinical evidence of sympathetic overactivity despite prolonged biochemical thyrotoxicosis.

Co-ingestion of insulin and levothyroxine appears to minimize symptomatic thyrotoxicosis risk, potentially through inhibition of thyroxine to triiodothyronine conversion and glucose homeostasis maintenance. This case highlights complex interactions in polydrug ingestions and suggests insulin may provide protection against thyroid storm in mixed overdoses.