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

Abstract

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&#x2009;mg/mL concentrations in four topical solutions over a 56&#x2009;day period. We hypothesised that amikacin would maintain chemical stability within the various solutions. METHODS AND MATERIALS: Amikacin was formulated to 10 and 30&#x2009;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&#x2009;+&#x2009;2&#x2009;mg/mL dexamethasone (ND). Samples were made in duplicate and stored at room temperature (25&#xb0;C) for 0, 7,14, 21, 28 and 56&#x2009;days. Amikacin content was quantified, in triplicate, by ultrahigh-performance liquid chromatography tandem mass spectrometry. RESULTS: The recovered amikacin concentrations for the 10&#x2009;mg/mL solutions ranged from 10 to 13.5&#x2009;mg/mL (mean 11.5&#x2009;mg/mL) with the exception of NA sample 2 at Day (D)0 (9.4&#x2009;mg/mL) and D7 (9.2&#x2009;mg/mL). The recovered amikacin concentrations for the 30&#x2009;mg/mL solutions ranged from 30 to 40.2&#x2009;mg/mL (mean 35.7&#x2009;mg/mL). No significant difference was seen between the amikacin concentrations at D0 compared to D56 for all solutions except 10&#x2009;mg/mL TE (P&#x2009;<&#x2009;0.001). CONCLUSIONS AND CLINICAL RELEVANCE: Amikacin maintained stability within TE, TC, NA and ND over 56&#x2009;days except when formulated at 10&#x2009;mg/mL within TE.