Thirteen-year-old (at least) Rosie, at right in the picture above, has gone mildly hyperthyroid. She's always been the most frenetically active member of our pride, but we never suspected that this could be a symptom until her most recent blood test earlier this year. We tried out Tapazole (a lower dose than for humans), but she doesn't tolerate it well (made her vomit and become a little reclusive). Being in good health otherwise, she was an excellent candidate for radioactive iodine treatment.
Kitties have two thyroids, and the doctors found one enlarged. This was presumably a benign tumor, and is responsible for the too-high level of thyroid hormone in her blood. Normal readings are four or less, and Rosie's was eleven. The other cat getting the treatment this week is older, and had a level of eighteen.
She got her pill on Monday, and spent three days in isolation at the hospital. She was discharged yesterday afternoon, acting normally. The half-life of I-131 is 8.1 days, so whatever small amount she hasn't excreted is down to about 70% of its radioactivity. We are to keep Rosie in isolation for two more weeks, staying more than three feet away from her in general. We can handle her, but are to limit that to 5-10 minutes two or three times a day. We are required to use a flushable litter (radioactive waste can't go into a landfill, but the water supply is apparently a fine destination) and to use gloves when cleaning up waste.
Interestingly, an aunt of mine just had the same treatment last week: I-131 pill, two days of isolation, plus a week or two of keeping her distance from people.
The doctor tells us that Rosie is unlikely to require any further medication; her other thyroid will probably suffice. We'll have her thyroid level checked again in a few weeks, and another precautionary blood test a few months later to ensure her liver function hasn't been impaired.
I'm hoping the radiation will give her superpowers. :D