I came across this fairly extreme intentional overdose a while ago:
Vet Hum Toxicol. 1999 Oct;41(5):323-6.
Severe symptoms following a massive intentional L-thyroxine ingestion.
Hack JB1, Leviss JA, Nelson LS, Hoffman RS.
NYC Poison Center, NY 10016, USA.
L-Thyroxine (T4) is commonly prescribed medication for hypothyroidism in humans and animals. Overdose has generally resulted in limited symptomatology managed with sedatives and beta-adrenergic receptor antagonists. We describe the largest acute T4 ingestion ever reported, which resulted in a profound thyrotoxicosis, resistant to treatment. A 34-y-old man ingested 900 (0.8 mg) tablets of veterinary T4 (720 mg) and was given 60 g of activated charcoal. He became lethargic on post-ingestion days 2 and 3; had vomiting, diaphoresis and insomnia on day 4; on day 5 he "looked like he had too much coffee", began "using a lot of words" and became agitated, assaultive and stopped speaking intelligibly; and on day 6 returned to the hospital combative and confused. He was diaphoretic, mydriatic, hyperreflexic, tremulous, with clear lungs and active bowel sounds, and received activated charcoal, haloperidol, diazepam, and phenobarbital, and was tracheally intubated. During hospitalization he was rehydrated, treated with propranolol and diazepam, but remained continuously tachycardic. On day 12 he became afebrile and his tachycardia resolved. Free T4 levels ranged from > 13 mcg/dL on day 6 to 1.2 mcg/dL on day 12. By discharge (day 15) he had lost 20 kilograms of body weight, but was clinically euthyroid 2 w later. This case suggests that large intentional T4 ingestions should be managed differently than current T4 overdose protocol.
PMID: 10509439 [PubMed - indexed for MEDLINE]
I think I would find it difficult to swallow 900 tablets!
And this accidental overdose:
To the Editor:
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.
One of the critical issues is that the effects can be minimal on the first day but gradually build up over days.
The idea that a veterinarian could be so adrift in her understanding of doses is worrying. At least for animals.