Inadvertent Ingestion of ‘Dog-Tabs’ by a Veterinarian

EDITOR’S NOTE: Don’t take medicine designed for dogs.

A 33-year-old veterinarian with Hashimoto’s thyroiditis and hypothyroidism, stable with a levothyroxine replacement dosage (thyroid-stimulating hormone, 0.9; normal, 0.4-5.0 mIU/L) of levothyroxine 50 μg/d, presented with mild anxiety, jitteriness, and insomnia. Repeat thyroid-stimulating hormone was undetectable. Serum total T4 was 15.4 μg/dL (normal, 6.0-10.0 μg/dL), and free thyroxine index was 14.9 (normal, 6-10). On further questioning, the patient realized she had recently run out of her prescribed levothyroxine tablets and had been taking levothyroxine “dog tabs” 0.5 mg/d, thinking that would be the same as the 50-μg tablets she had been prescribed, inadvertently taking 10 times the prescribed dose. Her levothyroxine therapy was discontinued, and repeat thyroid function studies 2 months later revealed a thyroid-stimulating hormone level of 5.1 mIU/L. The patient was restarted on levothyroxine 50 μg/d, and repeat thyroid-stimulating hormone level 2 months later was 1.0 mIU/L. The patient was instructed to take her prescribed levothyroxine tablets and not use her levothyroxine “dog tabs” in the future.

Hypothyroidism is common among humans and other mammals, including dogs.(1) The dosage requirements in dogs are substantially higher than in humans.

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— Harmeet Singh Narula, MD

This article originally appeared in the July 2012 issue of the The American Journal of Medicine.