Effect of bismuth subsalicylate on fecal microflora.

Several studies have documented the efficacy of bismuth subsalicylate (BSS) for the prophylaxis and treatment of bacterial diarrhea. It is not known what effect, if any, BSS has on the normal bowel flora. We quantitated the fecal flora in healthy volunteers before and after they took BSS. In the first group, 8 ounces of BSS was given on two successive days. In the second group, a standard oral intestinal lavage preparation (GoLYTELY) was used to clean the colon and then 8 ounces of BSS was given during a 4-hour period. There were no changes in total microbial counts or in counts of individual groups such as enteric bacteria, Pseudomonas, Staphylococcus, Bacteroides, or Clostridium difficile. On day 2 the yeast counts rose 2.4 log10 colony-forming units/g in the group taking 16 ounces of BSS but did not increase in the group taking 8 ounces of BSS plus GoLYTELY. The counts returned to pretreatment levels by day 7. These results show that a 1- or 2-day course of BSS, even with an oral intestinal lavage preparation, did not have significant effects on the normal microbial populations in the fecal microflora.