Metronidazole crystal patterns formed during the metamorphosis of topical carbopol gels.

Abstract

Metronidazole topical formulations such as gels, creams, and lotions are used in the treatment of bacterial vaginosis and inflammation lesions of rosacea. Metronidazole precipitating from a Carbopol-based gel resulted in the formation of unique, highly branched, curvilinear microstructures. In contrast, metronidazole precipitated as linear, acicular crystals from drug solutions. The reason for the change in crystal habit was investigated by preparing different custom-made solutions and gels. Custom-made solutions were prepared using different solvent systems. Custom-made gels were prepared using different concentration of pH modifier, carbopol and other excipients. Characterization studies were carried out on the recrystallized metronidazole using bright-field microscopy, polarized microscopy, scanning electron microscopy (SEM), Differential Scanning Calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and Powder X-Ray Diffractometry (PXRD). The results indicated that the change in crystal habit was likely due to the interactions between the nitro-imidazole moiety of metronidazole and the polymer without a change in the polymorphic form.