Gel Vehicles Are Not Inherently More Irritating than Creams

Background: It has been thought that topical gels are inherently more irritating than topical creams. Nevertheless, the irritancies of topical products are potentially quite variable, and a priori assumptions about relative irritancy of gels versus creams may not be accurate.

Purpose: To determine whether a metronidazole gel formulation is more or less irritating to the skin compared to metronidazole creams.

Methods: A total of 32 normal, healthy volunteers were tested using irritancy patches with 0.75% metronidazole gel and cream, 1% metronidazole cream, and petrolatum (used as the “negative control”). Blinded observers evaluated the application sites for signs of irritancy. A numerical score was assigned to these irritancy patch sites each day for 21 days, or until significant irritation developed, and cumulative irritancy scores were calculated for the study period. A mixed model of variance analysis was performed.

Results: After 21 days of evaluation, analysis of the mean cumulative irritancy scores for each of the agents used showed there to be no statistical difference in irritancy potential between the metronidazole gel and the metronidazole creams.

However, the 1% metronidazole cream was significantly more irritating than petrolatum. Conclusion: There was no significant difference in the cumulative irritancy potential of cream and gel preparations of metronidazole. The irritancy of topical formulations for treating rosacea should be considered on a case by case basis.