alex won't touch fortiflora either. an alternative is a good quality human probiotic from any health food store.
i use
Ultimate Flora Critical Care 50 Billion, but there are many others available. Whole Foods carries Ultimate Flora Critical Care 50 Billion. look for it in the refrigerated section. It's pricey, but a little bit goes a long way. i give alex about a third to a half capsule twice a day mixed in food a few hours away from giving the antibiotic. i also continue giving the probiotic for a few days after the abs are finished.
if you keep the bottle in the refrigerator it'll last a long time.
good luck!