Short-Term Metronidazole not Linked to Cancer

NEW ORLEANS—A large review with long-term follow-up of patients from Group Health Cooperative of Puget Sound, Seattle, seems to put to rest any fears that short-term use of metronidazole may cause cancer in humans.

Several factors have raised concerns about metronidazole: its mutagenic activity in vitro, its carcinogenic potential in animals, and its expanded use in humans. Previous studies that have attempted to assess its potential to cause cancer have been limited in patient size or duration of follow-up. None has looked at patients so long after exposure as the new study, which was reported at the 36th Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC).

Dr. Matthew Falagas, of New England Medicine Center and Tufts University School of Medicine, reported data on patients who received the drug as outpatients between 1975 and 1983. The 30,000 users included 21,000 females and 9,000 males (usually, the sexual partners of women treated for vaginal infections). Patients were compared with matched controls (nonusers).

The all-site incidence of cancer after the first 7 years of follow-up was 652 per 100,000 person-years for metronidazole users, compared with 662 for nonusers. No site was associated with an increased risk for cancer, and in the first 7 years after use, nonusers actually had a higher cancer rate, Dr. Falagas reported.