How old is the dog? It would be best to work with a vet and go with the recommended prescription food (check chewy.com). At least until the dog is stable, then you can evaluate your options. Has the dog been treated for infection? If so, he may need another round of antibiotics or other prescription medications along with the special diet.
Of course add water to his meals and provide frequent bathroom breaks, keep the bladder flushed.
If you buy it in a larger bag, divide it up and keep half of it in a tightly closed container in the freezer or fridg.
Use the other half first, store in a tightly closed container in a cool place.
