Use of Benzene-Free Carbomer 980 in the Formulation of Metronidazole Gel 0.75% and Demonstration of Equivalence with Carbomer 940.

The U.S. FDA currently recommends avoiding carbomer grades that contain benzene and recommends benzene-free alternatives (USFDA. Guidance for Industry: reformulating drug products that contain carbomers manufactured with benzene. Center for Drug Evaluation and Research (CDER), Pharmaceutical Quality/CMC. Published in December 2023. Available at: https://www.fda.gov/media/175083/download ). This means that if a finished product is authorized with a carbomer grade containing benzene, it needs to be replaced with a non-benzene carbomer grade. Such an update would also require detailed comparative studies-covering structure, performance, stability, and biological equivalence-to confirm consistent product quality and effectiveness. The current study attempted to replace Carbomer 940 (C940) with Carbomer 980 (C980) in 0.75% Metronidazole Gel. The two carbomer grades were characterized as powders using multiple spectroscopic techniques. A method for analyzing carboxylic acid content was developed and validated, using light-scattering resonance technology to improve accuracy. The formulation prepared with C940 and C980 was characterized for rheology, in vitro release and permeation, and stability, along with the reference formulation. Powder characterization shows slight differences in the absorption spectra across NMR and FTIR studies, while NIR spectra are the same. Additionally, C980 has a slightly higher molecular weight, degree of polymerization, apparent viscosity, and carboxylic acid content, but a lower water loss. The formulations prepared with C940 and C980 are rheologically equivalent to the reference formulation as assessed by flow curves, yield stress, linear viscoelasticity, and creep. The in vitro release and permeation study also demonstrates that the formulations prepared with C940 and C980 exhibit performance equivalence to the innovator formulation under the tested conditions. Hence, replacing the benzene-grade carbomer with the corresponding non-benzene-grade carbomer does not significantly affect product performance relative to the reference product.