General
Metronidazole topical gel has been reported to cause tearing of
the eyes. Therefore, contact with the eyes should be avoided. If a reaction
suggesting local irritation occurs, patients should be directed to use the
medication less frequently or discontinue use.
Metronidazole is a nitroimidazole and should be used with care in patients
with evidence of, or history of blood dyscrasia.
Information for patients
This medication is to be used as directed by the physician. It is
for external use only. Avoid contact with the eyes.
Drug interactions
Oral metronidazole has been reported to potentiate the
anticoagulant effect of coumarin and warfarin resulting in a prolongation of
prothrombin time. The effect of topical metronidazole on prothrombin time is not
known.
Carcinogenesis, mutagenesis, impairment of
fertility
Metronidazole has shown evidence of carcinogenic activity in a
number of studies involving chronic, oral administration in mice and rats but
not in studies involving hamsters.
Metronidazole has shown evidence of mutagenic activity in several in vitro bacterial assay systems. In addition, a
dose-response increase in the frequency of micronuclei was observed in mice
after intraperitoneal injections and an increase in chromosome aberrations have
been reported in patients with Crohn's disease who were treated with 200-1200
mg/day of metronidazole for 1 to 24 months. However, no excess chromosomal
aberrations in circulating human lymphocytes have been observed in patients
treated for 8 months.
PregnancyTeratogenic effectsPregnancy category B
There has been no experience to date with the use of
metronidazole topical gel in pregnant patients. Metronidazole crosses the
placental barrier and enters the fetal circulation rapidly. No fetotoxicity was
observed after oral metronidazole in rats or mice. However, because animal
reproduction studies are not always predictive of human response and since oral
metronidazole has been shown to be a carcinogen in some rodents, this drug
should be used during pregnancy only if clearly needed.
Nursing mothers
After oral administration, metronidazole is secreted in breast
milk in concentrations similar to those found in the plasma. Even though
metronidazole topical gel blood levels are significantly lower than those
achieved after oral metronidazole, a decision should be made whether to
discontinue nursing or to discontinue the drug, taking into account the
importance of the drug to the mother.
Pediatric use
Safety and effectiveness in pediatric patients have not been
established.