Quantitation of amphotericin B in plasma by second-derivative spectrophotometry

A method is described for determining amphotericin B in plasma using second-derivative spectrophotometry after deproteinization. The assay was based on the absorbance at 407.5 nm. The second-derivative spectrum recorded between 350 and 450 nm allowed identification of the analyte and showed absence of drug interference. Only bilirubin interfered at high concentration (greater than or equal to 50 mu mol l(-1)). The linear concentration ranges were 0.05-5.0 mg l(-1) (r = 0.999, slope = 2.731, intercept = 0.008). Between-day CV less than or equal to 9.7%, withinday CV less than or equal to 5.5%, analytical recovery close to 100% were suitable for clinical investigations. This method provides better specificity than direct absorbance, is simpler and faster than a high performance liquid chromatography assay and can be used routinely by any laboratory possessing a spectrophotometer with a derivative accessory. (C) 1998 Elsevier Science B.V. All rights reserved.