Metronidazole

What is metronidazole?

Metronidazole is an imidazole antibiotic that is used in the treatment of many protozoal and bacterial infections. It is available on prescription in various forms and strengths, including tablets, suspensions, solutions for injections, suppositories and topical creams and gels.

For skin conditions, topical metronidazole is indicated for the treatment of facial rosacea. In New Zealand topical metronidazole is a prescription medicine and is available as a 7.5 mg/g aqueous gel and cream (Rozex®) or a 5% generic gel. A foam preparation was also approved by the FDA and marked in the USA in July 2015.

A vaginal gel preparation of metronidazole is also available in some countries to treat bacterial vaginosis.

How does metronidazole work?

Metronidazole is an antiprotozoal and anaerobic antibacterial agent. When administered systemically via oral tablets or injection, metronidazole works by inhibiting bacterial DNA synthesis hence preventing the replication of bacteria. However the mechanisms by which topical metronidazole works in reducing inflammatory lesions of rosacea are unknown. Possible mechanisms of action include antibacterial and/or anti-inflammatory effects.

What is topical metronidazole used for?

Topical metronidazole is indicated for the treatment of inflammatory papules, pustules and erythema of rosacea. It should be applied twice daily, morning and evening, to the affected area after washing with a mild cleanser and patting dry. The average period of treatment is 3-4 months, although some improvement should be noticeable after 3 weeks of continued therapy. If significant improvement is seen after 3-4 months, your doctor may prescribe a further 3-4 months therapy. Treatment should be stopped if no clear clinical improvement is evident after the first 3-4 months.

Precautions when prescribed topical metronidazole

• Safety and effectiveness of topical metronidazole therapy has not been established in children.
• Do not use in or close to the eyes.
• Avoid or minimise exposure of areas treated with topical metronidazole to strong sunlight or other sources of UV light.
• Do not use topical metronidazole during pregnancy, as there may be a risk of teratogenicity (damage to the baby).
• Use topical metronidazole with caution in breastfeeding mothers.

Side effects of topical metronidazole

Side effects from the use of topical metronidazole are rare and usually mild. Side effects that should be reported to your doctor as soon as possible include:

• New skin condition or rash develops and/or rosacea worsens
• Numbness, stinging or tingling of the treated area
• Nausea

Other possible side effects that should resolve after continued use of topical metronidazole include:

• Local irritation
• Redness, itching or burning
• Dry skin
• Pigmentation disorders, when applied to facial skin
• Facial swelling
• Watery eyes