Almost any antibiotic can lead to C. difficile intestinal disease. Diarrhea usually begins 4 to 9 days after the patient starts an antibiotic, but it can also develop up to 8 weeks after an antibiotic is discontinued. Generally, C. difficile disease is caused by genotypes and strains that are resistant to the precipitating antibiotic. Penicillins, the cephalosporins, and clindamycin are most apt to precipitate the disease. However, even vancomycin—which is effective in treating C. difficile disease—can cause the disease. This probably occurs because vancomycin suppresses both normal flora and the vegetative forms of C. difficile, but not its spores. When vancomycin is discontinued, the spores germinate and the new vegetative forms flourish in the altered bacterial environment.