Major tarry diarrhea Thyroid meds to balme?

Well my cat 18yrs old has had a lot of trouble lately, check the "My kitty has lost 5lbs and may have cancer (help)" thread to get the back story. As of right now she is on Methimazole 5mg a day and I put her back on the Hills a/d wet food cause it's the only thing that seems to not make her throw up, She's been on dry food almost all her life.
This morning though after having some of the a/d over the past two days, she had the worst diarrhea ever and two more times after that. Her stools are almost black and tarry and liquidy. I think it's because of the thyroid meds and I'll see my vet tomorrow but is there anything I can do tonight to keep her from having more major diarrhea tonight? Should I give her some of her old dry food Purina One senior protection formula? or not feed her until I can get her to the vet tomorrow afternoon? Shes had three cans of the a/d food about a month ago to help her vomiting and she didn't have any trouble then so I'm thinking it's the meds. I just don't want to hurt her by not giving her any food until we see the vet which would make it about 18 hrs from now (6:30pm central time tomorrow)

Thanks for any help
FelineLuver

call YOUR local er vet..

I have to agree...black, tarry may mean blood in the stool and at her age, having diarhea of any sort is enough to dehydrate her.

ps I've used methimazole for my cats who had hyper-t for years...never had diarhea from it.

Well my vet gave me Centrine 0.2mg half a pill twice daily for the diarrhea and some Hills i/d dry food along with Purina FortiFlora 1 packet daily to give to her.

I guess all they can ever do is to treat symptoms instead of finding the cause and treating that.

I forgot to ask if I should try to see if the i/d food clears up the diarrhea first, before giving her more drugs. I dont know if the food would clog her up or not so I dont think it would be good for her to have a drug that stops diarrhea and a new food that might constipate her at the same time until I know the food goes through her ok. "if anyone thinks different, then please share your advice"

I've never had FortiFlora or products like that for my cat before so I would like to know anyone whos ever tried that kinda stuff before what there thoughts on these types of stomach probiotics, enzymes, etc... products are like (good,bad) Can they help a cat with heartburn, gerd, etc...
My kitty always burps after eating dry food which usually means gas build up or heartburn and what not, I told my vet but he kinda brushed it off.

Well as usual let me know your thoughts and opinions on the new meds/food that I was given and thanks for caring.

Keep Purr'n
FelineLuver