Simplicef is a cephalosporin-type antibiotic. I like it a lot for skin infections, but don't commonly use it for bladder infections. I don't generally grab SMZ-TMP as my first antibiotic choice, either. Truthfully, for a bladder infection and anal gland infection, I would have prescribed Clavamox.
Did you mention to the vet last night that your dog had a bad reaction to sulfa drugs in the past?
I don't know what happened with the chat, I answered you and then it said disconnected. When I asked the dr at the emergency clinic if the medication had another name (like a brand name) she said no. If she had told me Bactrim, I would have told her no. Then I called my regular vets office today and they wanted to give her Convenia. She has had that in the past for something else and it didn't seem to do anything. Plus she had a shot of that about 1 month ago. I don't like that drug anyway..too many negative stories...