Metronidazole - Prasco Laboratories

When one gram dose of Metronidazole Cream, 1%, was applied in a single application to the face of 16 healthy volunteers, low concentrations of metronidazole were detected in the plasma of 7 of the volunteers. The mean ± SD C_max of metronidazole was 27.6 ± 7.3 ng/mL, which is about 1% of the value reported for a single 250 mg oral dose of metronidazole. The time to maximum plasma concentration (T_max) in the volunteers with detectable metronidazole was 8–12 hours after topical application.

The mechanisms by which metronidazole acts in reducing inflammatory lesions of rosacea are unknown.

Safety and efficacy of Metronidazole Cream, 1%, were evaluated in two randomized vehicle-controlled clinical studies for the treatment of rosacea, which excluded patients who had nodules, moderate or severe rhinophyma, dense telangiectases, plaque-like facial edema or ocular involvement and those who had a history of not responding to metronidazole therapy for rosacea. Of the patients included in the efficacy database (n=416), there were 142 men and 274 women. Endpoint efficacy data comparisons for patients treated with daily Metronidazole Cream, 1%, or vehicle applications are listed below.

If a reaction suggesting local skin irritation occurs, patients should be directed to discontinue use of the medication. Conjunctivitis associated with topical use of metronidazole on the face has been reported. Contact with the eyes should be avoided. Metronidazole is a nitroimidazole and should be used with care in patients with evidence of, or history of, blood dyscrasia.

Patients using Metronidazole Cream, 1%, should receive the following information and instructions:

1. This medication is to be used as directed.
2. It is for external use only.
3. Avoid contact with the eyes.
4. Cleanse affected area(s) before applying Metronidazole Cream, 1%.
5. This medication should not be used for any disorder other than that for which it is prescribed.
6. Patients should report any adverse reaction to their physician.

Oral metronidazole has been reported to potentiate the anticoagulant effect of coumarin and warfarin resulting in a prolongation of prothrombin time. Drug interactions should be kept in mind when Metronidazole is prescribed for patients who are receiving anticoagulant treatment, although they are less likely to occur with topical metronidazole administration because of low absorption. (See CLINICAL PHARMACOLOGY, Pharmacokinetics section)

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.

In several long term studies in mice, oral doses of approximately 225 mg/m²/day or greater (approximately 37 times the human topical dose on a mg/m² basis) were associated with an increase in pulmonary tumors and lymphomas. Several long term oral studies in the rat have shown statistically significant increases in mammary and hepatic tumors at doses >885 mg/m²/day (144 times the topical human dose).

Metronidazole has shown evidence of mutagenic activity in several in vitro bacterial assay systems. In addition, a dose-related increase in the frequency of micronuclei was observed in mice after intraperitoneal injections. An increase in chromosomal aberrations in peripheral blood lymphocytes was reported in patients with Crohn's disease who were treated with 200 to 1200 mg/day of metronidazole for 1 to 24 months. However, in another study, no increase in chromosomal aberrations in circulating lymphocytes was observed in patients with Crohn's disease treated with the drug for 8 months.

In one published study, using albino hairless mice, intraperitoneal administration of metronidazole at a dose of 45 mg/m²/day (approximately 7 times the human topical dose on a mg/m² basis) was associated with an increase in ultraviolet radiation-induced skin carcinogenesis. Neither dermal carcinogenicity nor photocarcinogenicity studies have been performed with Metronidazole or any marketed metronidazole formulations.

After oral administration, metronidazole is secreted in breast milk in concentrations similar to those found in the plasma. Even though blood levels taken after topical metronidazole application 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 and the risk to the infant.

Safety and effectiveness in pediatric patients have not been established.

Store at controlled room temperature: 20 to 25°C (68 to 77°F).