Evaluation of Compatibility and Stability of Compounded Otic Solutions Containing Enrofloxacin Over a 20-Day Period.

Avoid compounding enrofloxacin with tris-EDTA or antifungals; use sterile water only.

This study evaluated the compatibility and stability of compounded otic solutions containing enrofloxacin at two concentrations (100 mg/mL and 22.7 mg/mL) combined with various additives over a 20-day period. Twelve formulations were assessed using physical examination, pH analysis, mass spectrometry, and high-performance liquid chromatography. Results demonstrated excellent compatibility and stability when enrofloxacin was combined with sterile water alone, with no significant degradation observed. However, formulations containing tris-EDTA showed substantial enrofloxacin degradation by day 10, with concentration decreases ranging from 25.4% to 49.8% depending on enrofloxacin concentration and presence of dexamethasone. All solutions containing antifungals (ketoconazole or miconazole) exhibited immediate incompatibility issues including ingredient separation, precipitate formation, and exothermic reactions, preventing analysis. The study concluded that clinicians should avoid compounding enrofloxacin with tris-EDTA or antifungal agents due to significant incompatibility and instability concerns that could compromise therapeutic efficacy in otitis treatment.

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