Diarrhea associated with clindamycin and ampicillin therapy: preliminary results of a cooperative study.

Patients treated with clindamycin were monitored for development of diarrhea and colitis in a cooperative study at three hospitals in Edmonton, Toronto, and Winnipeg, Canada. Ampicillin-treated patients were matched with clindamycin-treated patients. Diarrhea occurred in 62 (18%) of 343 clindamycin-treated patients compared with 16 (5%) of 315 ampicillin-treated patients (P less than 0.001). Among the three hospitals, the rate of diarrhea associated with clindamycin therapy ranged from 10% to 23% compared with 0 to 10% for ampicillin therapy. The only identified risk factor in the development of diarrhea was increased age; clindamycin-associated diarrhea occurred in 18 (46%) of 39 patients greater than or equal to 60 years old. No correlation was observed between the risk of diarrhea and the duration of treatment, total dosage of drug, route of administration, or type of underlying disease. Pseudomembranous colitis was diagnosed in seven (2%) of 343 patients treated with clindamycin and in one (0.3%) of 315 patients treated with ampicillin.