Cats & amitriptyline

[urbancowgirl]

I've posted about my problem child here before. He's a 12 year old neutered male that has peed outside the litter box on occasion for his entire life. We moved cross-country to a new (temporary) apartment about four months ago. He started peeing all over the carpet in this apartment, so our vet put him on amitriptyline. He's been on the medication for a little over two months and it was working well. He completely stopped peeing outside of his litter box until last night, when he took a nice big whiz on the carpet.

My question is this: If you have a cat (or other pet) on amitriptyline, have you had to increase the dosage? I'm wondering whether I should ask my vet to increase the dosage because the medication seems to be losing its effectiveness. We noticed over the past two weeks that his agitation and fixation on food (two traits he expressed prior to the medication) were increasing after virtually disappearing while on the medication. And now he seems to want to pee on the carpet again. TIA for any advice you have!