Yesterday we took Hamilton to the Fresh Pond Animal Hospital to review his hyperthyroid situation and try to figure out why he'd been throwing up for 24 hours. They rehydrated him, gave him some pecid and took another round of blood tests (these vet bills add up, don't they?).
The doctor thinks the hyperthyroid medication might be causing him to have a sick stomach. So we've taken him off the medication for now and he's on a bland diet of I/D cat food (which he promptly threw up when we got home) and baby food (which he seems to finally be keeping in over the last 24 hours).
Happily, the test results seem to indicate that his kidneys are OK. So at 12 years old, Hamilton might indeed be a candidate for the iodine irradiation treatment, which is a good thing if he can't stay on the meds. We're gearing up now for that news, and to prepare for the procedure if he can have it.
UPDATE: Unfortunately, just after writing the above, I went upstairs and found Hamilton stuffing himself with the dried Science Diet we had left out for one of the Scottish Folds, without properly locking him behind closed doors with it. This is the problem with having five cats in the house, all on different diets. We'll see if the Science Diet stays in Hamilton's stomach today! Thank goodness we just bought a new battery-operated carpet spot remover!