Metronidazol Viñas (Metronidazole)

Metronidazole is used topically to manage dermatological infections and inflammatory conditions caused by anaerobic bacteria and protozoa.

• Rosacea: reduces inflammatory papules, pustules and persistent facial erythema, improving overall skin appearance.
• Acne vulgaris: decreases Propionibacterium acnes colonization and associated inflammation, leading to fewer papules and pustules.
• Bacterial skin infections: eradicates susceptible anaerobic bacteria such as Staphylococcus aureus and Bacteroides species, facilitating wound healing.

• Metronidazole penetrates microbial cells and undergoes reduction by anaerobic electron transport proteins, generating reactive nitro radicals. These radicals interact with DNA, causing strand breakage and loss of helical structure, which inhibits nucleic acid synthesis and results in cell death of anaerobic bacteria and protozoa. The selective activation in low‑oxygen environments spares aerobic host cells, providing a therapeutic window for topical application.

Topical metronidazole may cause local and systemic adverse reactions, most of which are mild and reversible.

Common Side Effects

• Skin irritation: redness, burning or stinging at the application site, usually transient.
• Dryness: mild scaling or dryness of treated skin that resolves with moisturizers.
• Pruritus: itching sensation around the area of use, often relieved by discontinuation.
• Hyperpigmentation: temporary darkening of the skin that may persist for weeks after therapy.

Serious or Rare Side Effects

• Allergic reaction: urticaria, facial swelling, or severe rash indicating hypersensitivity, requiring medical evaluation.
• Stevens‑Johnson syndrome: rare severe mucocutaneous reaction with blistering and detachment of skin, necessitating immediate discontinuation and emergency care.

When using topical metronidazole, certain precautions help ensure safe and effective therapy.

• Pregnancy: Category B; use only if clearly needed after risk‑benefit assessment.
• Breastfeeding: Small amounts may be excreted in milk; consider discontinuation if infant shows irritation.
• Skin integrity: Avoid application on extensive open wounds or damaged skin to reduce systemic absorption.
• Allergy history: Do not use if known hypersensitivity to metronidazole or other nitroimidazoles.
• Concomitant therapy: Monitor for increased irritation when combined with other topical irritants or retinoids.
• Store at ambient temperature: keep below 25 °C in the original container, protect from moisture and direct sunlight.

Metronidazole can interact with other medicines; awareness of significant and moderate interactions guides safe co‑administration.

Major Interactions (Avoid)

• Alcohol: may cause a disulfiram‑like reaction with flushing, nausea and tachycardia.
• Warfarin: potentiates anticoagulant effect, increasing risk of bleeding.

Moderate Interactions (Monitor Closely)

• Lithium: may increase lithium levels; monitor serum concentrations.
• Cytochrome P450 inducers (e.g., rifampicin, carbamazepine): may reduce metronidazole efficacy.
• Topical steroids or retinoids: may enhance local irritation.
• Antifungal azoles (e.g., ketoconazole): potential additive toxicity; observe for adverse skin reactions.