Comparison of Microbiological and High-Performance Liquid Chromatographic Methods for Determination of Clarithromycin Levels in Plasma

An agar well diffusion bioassay method for determination of clarithromycin in human plasma, using Micrococcus Luteus ATCC 9341 as the assay organism, was compared with a selective high-performance liquid chromatographic (HPLC) method with UV detection. Spiked plasma was used to prepare standard and control samples for both methods. The results of the bioassay analyses with spiked plasma samples were concordant by HPLC methods (R2 =0.871, P < 0.001).The Bland-Altman method also showed good agreement between the results of two methods. HPLC demonstrated an improved precision (0.88-19.86% versus 4.51-26.78%) and accuracy (99.27-103.42 % versus 78.52-131.19 %), compared to those of the bioassay method. The range of linearity obtained by both methods (from 62.5 to 3000 ng/ml for HPLC and from 250 to 3000 ng/ml for the bioassay) includes the range of concentrations of clarithromycin which are considered clinically relevant. However, comparison between HPLC and microbiological assays after oral administration of clarithromycin in healthy volunteers indicated significant differences between the two methods in mean plasma concentration–time profiles. The Bland-Altman method revealed no agreement between the two methods, which can be explained by the presence of active metabolites of clarithromycin in plasma.