Try Earthborn Holistic Meadow Feast or Nature's Variety Instinct LID Turkey. But more important than that is adding back the probiotics that the medications killed off. A little canned pure pumpkin for a healthy fiber source may help, but in this case may not, but pumpkin is cheap so IMHO worth a try, about 1 teaspoon per 10 lbs. You can freeze the extra into ice cubes and have it on hand, for future need. Digestive enzymes may help too.
Unfortunately, I know exactly what you are talking about. My dogs have been treated 3 or 4 times for giardia. Our vet recommended not only pre and probiotics and digestive enzymes. He also suggested supplements to heal their intestines such as DGL, marshmallow root and plantain. I didn't have a clue what they were. Lol! After research, I found that dogaware dot com has a great section on digestive orders with supplements that contained some of these. I've used Gastriplex by Thorne, Vetri-Probiotic BD, and Phytomucil by Animal Essentials with success. Also, make sure to get the dog retested because it often takes more than one treatment to get completely rid of it. Good luck. And, oh yes, of course, check with your vet first.
My Lab got some kind of intestinal infection…giardia,salmonella etc from 4Health when they had the recall a while ago. my vet put him on rice and boiled chicken for a week plus antibiotics and probiotics.I have found that the probiotics help to straighten out his tummy whenever it isnt feeling well. He eats the powder mixed in his food.I kept him on the probiotics for a month after his infection.