Q: Our son, 38, was put on a 10-day course of Cipro because the doctor thought he had a prostate infection. A few weeks later, he had profuse diarrhea. Tests showed he had Clostridium difficile infection. He was treated with Flagyl, and the diarrhea cleared up. Three months later he had a cystoscopy (a scope exam of the bladder) and was given only two Cipro pills to prevent infection. Again he developed diarrhea, and again he was treated with Flagyl. The diarrhea stopped, but not as quickly. He had another cystoscopy but refused to take antibiotics. After it, he had rectal bleeding and was put on vancomycin. Each return of C. difficile is more severe. What's going on? Our son eats yogurt with live bacteria daily. Should he take probiotics?

A: C. difficile-associated disease is a rare complication of antibiotic treatment. C. difficile is a bacterium that's widespread in nature. Some strains of the germ make a toxin that attacks the colon lining to cause diarrhea. When a person takes antibiotics, however, good bacteria can be killed, and the C. difficile bacterium proliferates and can lead to diarrhea. Often, simply stopping the antibiotic ends the diarrhea. In more-severe cases, antibiotics that target the C. difficile germ have to be prescribed. Flagyl (metronidazole) and vancomycin are two such drugs.

Probiotics -- beneficial bacteria -- are sometimes recommended to reconstitute the good bacteria in the colon. Your son's yogurt with live bacteria is a probiotic. There are others.

Your son has an excellent chance of recovery, but it can take time.