Determination of amikacin stability at 1% and 3% concentrations in four topical solutions over a 56‐day period

Background Anecdotally, amikacin has been added to compounded topical preparations for the management of canine bacterial otitis externa. However, the stability of amikacin within these solutions is unknown. Hypothesis/Objectives The purpose of this study was to determine the stability of amikacin at 10 and 30 mg/mL concentrations in four topical solutions over a 56 day period. We hypothesised that amikacin would maintain chemical stability within the various solutions. Methods and materials Amikacin was formulated to 10 and 30 mg/mL (1% and 3%) concentrations within four topical solutions: tris‐EDTA (TrizEDTA Aqueous Flush) (TE); 0.15% chlorhexidine gluconate and tris‐EDTA (TrizCHLOR Flush) (TC); 0.9% NaCl (NA); and 0.9% NaCl + 2 mg/mL dexamethasone (ND). Samples were made in duplicate and stored at room temperature (25°C) for 0, 7,14, 21, 28 and 56 days. Amikacin content was quantified, in triplicate, by ultrahigh‐performance liquid chromatography tandem mass spectrometry. Results The recovered amikacin concentrations for the 10 mg/mL solutions ranged from 10 to 13.5 mg/mL (mean 11.5 mg/mL) with the exception of NA sample 2 at Day (D)0 (9.4 mg/mL) and D7 (9.2 mg/mL). The recovered amikacin concentrations for the 30 mg/mL solutions ranged from 30 to 40.2 mg/mL (mean 35.7 mg/mL). No significant difference was seen between the amikacin concentrations at D0 compared to D56 for all solutions except 10 mg/mL TE (P