Three more thoughts to add to the good information that others posted already.

Make sure your probiotic is of the highest quality you can afford (preferrably a company who makes their assays public). Studies have been done and more often than not the number of live bacteria are grossly under what is advertised b/c many of them had already died off. Even some pharmaceutical grades were guilty of this so your best bet really is a company that will provide you with the details of their analysis.

Also make sure to get an extra strength probiotic when taking antibiotics, not just the regular strength.

Last, make sure to take the probiotic away from the antibiotic (not together). The antibiotic will just kill what you take in.

Wanda