Antibacterials, antifungals and antivirals cannot tell the difference between a friendly organism and a pathogen. They only recognize resistances of cells and these resistances vary from organism to organism. Friendly bacteria can be killed and are killed by many of the herbs and drugs and compounds we ingest to kill the unfriendlies. Friendly bacteria do not have a better resistance to treatments than pathogens. Hence the common recommendation to leave a window of at least two hours or better between the time you take a probiotic and the time you take an antibacterial or antifungal. This permits the stomach largely to empty and the body to absorb maximum amounts (or in the case of a probiotic to permit maximum growth in the intestine) before the next onslaught. I usually take probiotics last thing before going to bed so they may grow all night and take the fungicide (or antibacterial or antiviral) in the morning. This gives the probiotic maximum time to establish populations in the GI. In the case of something like Threelac or Fungal Defence or Nature's Biotic where ingestion is recommended more than once during a 24 hour period, I try to leave a time interval of a minimum of two hours between the last dose of fungicide or bactericide (whether it is a natural remedy or a prescription drug) and the probiotic.