My three cats have entered into their mature cat years now. So far, Nee Nee is diabetic, Gray Boy (pictured) has a thyroid condition, and Sissy's kidney's are going.
The most recent diagnosis is Sissy, and when I was getting ready to bring her to the vet (due to a general lack of appetite, which is so not like her since she takes after her mom and is normally a little piglet) my DH predicted, "It will have some sort of syringe involved." This is because we give insulin shots to one cat and thyroid meds via a syringe to the other cat already.
His prediction was correct. Along with a special diet, we will have to start giving her weekly injections of liquids to go under her skin as a way to hydrate her because her kidneys no longer are able to process them. Luckily - I guess - I've had to do this before with one of our dogs (who is no longer with us after 16 1/2 years). That and the fact that I'm used to giving shots now, it didn't faze me too much. Now, of course, how the girl cat will handle it is a whole different story.