Kutyuska ,
My thoughts run like this for problems that do not resolve with the usual treatment for Giardia. Since there are no drugs certified by the FDA to treat Giardia , what we are left with is what works best. Keep in mind that Ace may have something else besides the Giardia causing problems.
First , if all meds for Giardia are finished I would try a diet or dog food that you know does not cause loose stool that Ace has been on in the past. His stomach may be messed up from all the meds , so , give some probiotics and perhaps a little pure pumkin in a can ( not pumpkin pie mix) and do not over feed. Sometimes I just feed plain boiled chicken and rice to see how dog does.
Please note that not all dogs can eat a rich food like Acana. Also keep in mind the many recalls we have had with major pet food mfg.
After trying the above you will have a good idea where you stand and will be better able to make informed choices if problem is not resolved. Let us know how Ace is doing over the next few days. If symptoms return , please post and describe as best possible.
EDIT: I read your post again , and , if the symptoms that continue are loose mucosy stool with strong odor I would treat with Drontal Plus and follow this with the sulfadimethox for treatment of Coccidia ( 14 days , dosed by weight ) because Giardia and Cocci will often have neg test results.
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Food for thought:
Dormant Giardia cysts may be present in dogs with no symptoms , however , it is also possible to have active cysts that are not shedding and thus will not show up in fecal float/stain test. Fecal ELISA Snap® Giardia test is best. IMO
Ace had a Vet diagnosis of Giardia and has been treated with Metronidazole more than once and you are still having problems. ( Metronidazole is only about 60% effective for Giardia treatment in dogs. ) Metro is standard treatment , however , in the more problematic or resistant cases of Giardia there are meds that have proven better results in dogs.
What I do is treat with Metronidazole for seven consecutive days ( dosed by dog weight ) and SafeGuard ( dosed by weight ) for three consecutive days. The SafeGuard can follow the Metro or be given at same time.
This treatment has worked for me very well , however, in your case given that you have a Vet confirmed diagnosis for Giardia. If problem still exists I would most likely ask my Vet to follow this treatment with Drontal Plus because it's efficacy has been shown to far exceed that of Metronidazole alone in treatment of Giardia in dogs. You should not need to pay another Vet visit to buy the Drontal Plus because you have just been to the Vet and problem not resolved.
Helpful Note: Dogs can reinfect themselves by grooming and ingesting fecal matter that contain active cysts. Along with treatment , dogs should be bathed with shampoo to remove fecal debris and associated cysts. Clean or remove bedding to be safe.
Also , try taking Ace to a different potty area with no other animal feces in sight.
If you have done all the above , IMO , the next step is to treat for Coccidia as the symptoms are almost exactly the same and are missed by many Vets that I have used. In fact I have had the exact same issue that you and Ace have gone through and it ended up being Coccidia.
Drontal Plus is a med you will have to get from your Vet , however , all other meds we have discussed are available online or from farm or pet supply stores.
Consider this a systematic process of elimination and you will find the cause I am sure.
Best , oldhounddog