General: Topical Metronidazole (Metrogyl) has been reported to cause tearing of the eyes. Therefore, contact with the eyes should be avoided. If a reaction suggesting local skin irritation occurs, patients should be directed to use the medication less often or discontinue use. Metronidazole is a nitroimidazole and should be used with care in patients with evidence of, or history of, blood dyscrasia.
Carcinogenicity and Mutagenicity: Metronidazole (Metrogyl) is mutagenic in bacterial assays, and its hydroxy metabolite even more so, but studies of mammalian cells in vitro and in vivo have not consistently demonstrated a mutagenic effect. Similarly, there is no uniformity in the limited data concerning genotoxicity in humans, and although Metronidazole (Metrogyl) has been classified as carcinogen in animals, the evidence of human carcinogenicity is ambiguous. There was no appreciable increase in the incidence of cancer in a retrospective study of 771 patients given Metronidazole (Metrogyl) for vaginal trichomoniasis, nor in another similar study of 2460 patients. The first study did show an excess of cases of lung cancer, although all 4 were in women who were smokers. Subsequent follow-up to 1984, covering a period of 15 to 25 years, still showed an excess of lung cancer cases even after allowing for smoking status. However, this follow-up also continued to show no significant increase overall in cancer-related morbidity or mortality. Follow-up of the patients from the second study for 11 to 15 years to 1984 also showed no increase in the overall incidence of cancers nor did it confirm any increase in lung cancer.
Use in Children: Safety and effectiveness in pediatric patients have not been established.
Use in the Elderly: While specific clinical trials in the geriatric population have not been conducted, sixty-six patients aged 65 years and older treated with Metronidazole over ten weeks showed comparable safety and efficacy as compared to the general study population.