Differences in Rheological Properties between Brand and Generic Metronidazole Gels and Their Potential Impact on Malodor Management in Cancer Survivors.

INTRODUCTION: Malignant fungating wounds often produce strong malodors caused by anaerobic bacterial proliferation, which severely impairs the quality of life of cancer survivors and their caregivers. Topical metronidazole is widely used as a first-line option for odor control; however, differences in the rheological (Q3) attributes between brand-name and generic gel formulations may influence spreadability, retention on the wound surface, and overall usability. The study aimed to compare the rheological properties of brand and generic metronidazole gels marketed in Japan and to discuss their potential impact on malodor management. METHODS: Brand (RozexⓇ Gel 0.75%) and generic metronidazole gels were evaluated using a rotational rheometer. Flow behavior, thixotropy, viscoelasticity (G', G″), linear viscoelastic region (LVR), and frequency sweep responses were measured at 25℃. Excipients were compared qualitatively based on package inserts. RESULTS: Both formulations exhibited shear-thinning behavior; however, the brand gel showed consistently higher viscosity across all shear rates, with a pronounced difference at low shear rates relevant to wound application. The brand product demonstrated a narrower thixotropic hysteresis loop (approximately 26-fold difference), indicating faster structural recovery. Viscoelastic measurements showed higher G' values and a wider LVR for the brand gel, suggesting a stronger gel network. Frequency sweep analysis revealed strong-gel behavior for the brand formulation, whereas the generic gel exhibited weak-gel characteristics. These rheological differences corresponded to differences in base polymers-carboxyvinyl polymer in the brand gel and hydrophobically modified hydroxypropyl methylcellulose in the generic. CONCLUSIONS: Although containing identical active ingredients, the two formulations exhibit distinct rheological profiles that may affect clinical handling and usability in malodor management. Q3 attributes should be considered when selecting topical products for cancer survivors with fungating wounds.