Side Effects of Noritate (metronidazole)

Noritate (metronidazole cream) is a topical preparation (applied to the skin) of the antibiotic metronidazole used to reduce the swelling and redness caused by acne rosacea. 

The mechanism through which Noritate cream reduces the symptoms of acne rosacea is not known. 

Common side effects of Noritate include

• irritation,
• skin dryness,
• scaling, and
• itching at the site of application.

Serious side effects of Noritate include

• severe skin stinging or burning.

Drug interactions with Noritate cream are unlikely because only small amounts of Noritate are absorbed into the body when Noritate cream is applied to the skin.

• Oral metronidazole interacts with warfarin, increasing the blood-thinning effects of warfarin. It is not known whether the small amounts of Noritate absorbed via the skin can cause the same interaction. 

There are no adequate studies of Noritate cream in pregnant women. 

When metronidazole is administered orally it is secreted into breast milk in concentrations similar to the concentration in the mother’s body. Therefore, small amounts of metronidazole that are absorbed into the body when Noritate cream is used may be secreted into breast milk. Consult your doctor before breastfeeding.

Side effects are rare and minor. These include:

• irritation,
• skin dryness,
• scaling, and
itching at the site of application.

Individuals that are allergic to metronidazole should not use metronidazole cream.

Safety data from 302 patients who used Noritate (metronidazole) (n=200) or vehicle control (n=102) once daily in clinical trials and experienced an adverse event considered to be treatment-related include:

• application site reaction (Noritate (metronidazole) 1, vehicle 1),
• condition aggravated (Noritate (metronidazole) 1, vehicle 0),
• paresthesia (Noritate (metronidazole) 0, vehicle 1),
• acne (Noritate (metronidazole) 1, vehicle 0),
• dry skin (Noritate (metronidazole) 0, vehicle 2).

The majority of adverse reactions were mild to moderate in severity.

Two patients treated with Noritate (metronidazole) once daily discontinued treatment because of adverse events: one for a severe flare of comedonal acne and one for rosacea aggravated.

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 Noritate (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.

Carcinogenesis, Mutagenesis and 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.
• 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 Noritate or any marketed metronidazole formulations.

Pregnancy

• Teratogenic Effects: Pregnancy Category B. There are no adequate and well controlled studies with the use of Noritate (metronidazole) in pregnant women.
• Metronidazole crosses the placental barrier and enters the fetal circulation rapidly.
• No fetotoxicity was observed after oral administration of metronidazole to rats or mice at 200 and 20 times, respectively, the expected clinical dose.
• However, oral metronidazole has shown carcinogenic activity in rodents. Because animal reproduction studies are not always predictive of human response, Noritate (metronidazole) 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 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.

Pediatric Use

• Safety and effectiveness in pediatric patients have not been established.