The aim of this study was to prepare a topical water-in-oil type microemulsion containing
metronidazole and to compare its effectiveness with a commercial gel product in the treatment of
rosacea. A pseudo-ternary phase diagram (K(m)=2:1) was constructed using
lecithin/
butanol/
isopropyl myristate/water. The microemulsion was chosen from the microemulsion region in the phase diagram. The formulation was a water-in-oil type microemulsion (droplet size: 11.6 nm, viscosity: 457.3 mPa·s, conductivity: 1.5 µs/cm, turbidity: 6.89 NTU) and the addition of the
metronidazole did not alter the properties of the system. The release experiment showed that the release rate of
metronidazole from the commercial gel product was higher than that of the microemulsion. Stability experiments showed that the
metronidazole microemulsion remained stable for at least 6 months; none of the characteristic properties of the microemulsion had changed, the system retained its clarity and there was no sign that crystallization of
metronidazole has occurred. Microemulsion was compared to a gel product in a randomized, double-blind, baseline-controlled, split-face clinical trial for the treatment of patients. After the 6-week treatment period there was a statistically significant difference in reduction of the main symptoms of
rosacea. Of the patients treated with the microemulsion, 17% experienced complete relief from inflammatory lesions, and 50% from
erythema. The microemulsion resulted in complete relief in 38% of the patients with
telangiectasia while the commercial product did not provide any relief of
telangiectasia symptoms. In conclusion, the microemulsion containing
metronidazole was found to be more effective in reducing the symptoms of
rosacea compared to the commercial gel product.