TINIDAZOL for Giardia - effectiveness of it, generic form? and where to get it ?

Our vet said that hounds (bassets & beagles) seem to be more difficult to cure Giardia than other dogs. It seems to be true as I've read online where people had great success with one or two treatments of the dewormer (panacure) with little problem.

We have tried Fish zole & panacure for our Basset hound's Giardia - repeatedly! (She has tested positive for it repeatedly)

The wormer (panacur) does not seem to help at all! Her stool never gets normal. Vet suggested a 21 day treatment. She refused to eat anything and was getting skinny after about day 13 so that was impossible to go the full 21 days. And her poop never changed anyway. We waited to see if the soft poop was side effect of panacure which can cause diarrhea. But after a few days off of it, she still had it.

We then started again the Fish Zole. She was better for a couple of days and would start having more normal poops. But once off of the Fish Zole for a day or two, she's back to terrible runs - even like coffee late! We're getting ready for yet another round of Fish Zole. But we have heard about TINIDAZOL . I imagine our vet would write a script for it but was wondering if anyone knew the generic for and where we could purchase it. Fish Zole is easily found and much cheaper that way than as a prescription from vet.

Thanks in Advance!