Ah, yes that is an entirely inappropriate treatment in that case. Actually in cases of an accidental overdose such as the one you described generally does not result in toxicosis. Where an overdose of thyroid in a human can be very impactful, dogs can tolerate doses of up to 0.2 milligrams per kilogram before we take action. Generally the signs we see tend to be GI in nature below that threshold dose.
Now, we do start to see tachycardia and neurological stimulatory effects at doses higher than that, but treatment is geared towards mitigating the signs until the thyroid problem has cleared from the system, rather than potassium iodide. The standard of treatment in an acute overdose where clinical signs are expected are as follows:
-Administration of activated charcoal with a cathartic
-Clinical monitoring and providing fluids as needed
-Diazepam as needed for seizures, hyperactivity, and tremors
-Propranolol for tachycardia
-Lidocaine for ventricular arrhythmias
-Monitoring of blood work, serum thyroid levels, and electrolytes
They are then kept in the clinic until clinical signs resolve. Because of a dog's higher tolerance to thyroid hormones, they generally h ave a very good prognosis with treatment.