Fair warning: the stuff has sugar in it. Yes, it's organic sugar, but if you're dealing with a yeast overgrowth from the antibiotics, it's kind of going to defeat the purpose, as sugar feeds the yeast. It WILL have probiotics in it, though, so I'd say it's better than doing nothing.
Frankly, I'd just go out of the way and do the health food store and anything else in that direction a day or three sooner - easier to do!
BTW, I did find that the pharmacy in our local grocery store (Giant, similar to Safeway but not as widespread) carried probiotic powder w/o a prescription. I had to ask for it, but they had it in a box. This was back before I knew to refrigerate the stuff, though...
Anyway, if yours has them as well, a special trip might not be necessary.