Evaluation physicochemical stability of metronidazole gel 1 %formulation

Abstract

Introduction : The stability of topical formulations is critical for their efficacy and safety. This study aimed to formulate
a 1% metronidazole gel for treating rosacea and to evaluate its physicochemical stability.
Methods: This study formulated gels using Carbopol 935 as the gelling agent. The prepared samples contained
metronidazole on its own or supplemented with either methylparaben or EDTA as a preservative. To assess stability, the
formulations were stored for 30 days under two conditions : room temperature and refrigeration. Their stability was
evaluated through organoleptic inspection, alongside monitoring of pH and conductivity, and analysis via Fourier-
Transform Infrared (FTIR) spectroscopy employing an Attenuated Total Reflection (ATR) accessory.
Results: Macroscopic analysis revealed no changes in the gels' homogeneity or color over time. Measurements of pH and
conductivity showed no significant differences (p>0.05) for most formulations, except for a predictable pH decrease in
the EDTA-containing gel. Critically, FTIR analysis confirmed the absence of chemical interactions. The characteristic
metronidazole peaks at ~1636 cm⁻¹ (C=C, C=N stretching) and ~3313 cm⁻¹ (C-H stretching) remained unchanged in
position and intensity in all formulations after 30 days, with no appearance of new spectral bands.
The results from all analytical techniques demonstrate the stability of the 1% metronidazole gel. The consistency of the
FTIR spectra confirms the absence of chemical degradation or incompatibility between metronidazole, Carbopol 935,
and the preservatives. It is concluded that Carbopol 935 is a suitable polymer for formulating a stable topical
metronidazole gel, which remains chemically stable for at least 30 days, even at room temperature.