A look at the safety of metronidazole 1% gel: cumulative irritation, contact sensitization, phototoxicity, and photoallergy potential.

Rosacea is a common, recurrent, inflammatory dermatologic disorder characterized by the presence of facial erythema, visible blood vessels, papules, and pustules. The condition may cause serious psychologic morbidity and may significantly affect quality of life. The first topical rosacea therapy approved by the US Food and Drug Administration was metronidazole for the treatment of inflammatory lesions and erythema. Previously, metronidazole was available as a 0.75% gel. Improved solubility was achieved in a new, stable, aqueous gel that permitted the formulation of metronidazole 1.0%. This new formulation is highly spreadable, easy to use, cosmetically friendly, mild to the skin, nondrying, and moisturizing. The safety of metronidazole 1% gel was determined by the evaluation of its cumulative irritation, contact sensitization, phototoxicity, and photoallergy potential in healthy male and female patients. In this formulation, metronidazole was not irritating under occlusive application. Additionally, metronidazole 1% gel had a low potential for causing sensitization reactions, and no evidence suggested phototoxic or photoallergic reactions.