Determination of albendazole and its main metabolites in ovine plasma by liquid chromatography with dialysis as an integrated sample preparation technique

Albendazole is a benzimidazole derivative with a broad-spectrum activity ag ainst human and animal helminth parasites. Ln order to determine the main p harmacokinetic parameters in sheep after oral and intravenous administratio n of a new formulation of albendazole (an aqueous solution), a fully automa ted method was developed for the determination of this drug and its main me tabolites, albendazole sulfoxide (active metabolite) and sulfone in ovine p lasma. This method involves dialysis as purification step, followed by enri chment of the dialysate on a precolumn and liquid chromatography (LC), All sample handling operations were executed automatically by means of an ASTED XL system. After conditioning of the trace enrichment column (TEC) packed with octadecyl silica with pH 6.0 phosphate buffer containing sodium azide, the plasma sample, in which a protein releasing reagent(1 M HCl) containin g Triton X-100 was automatically added, was loaded in the donor channel and dialysed on a cellulose acetate membrane in the static-pulsed mode. The di alysis liquid consisted of pH 2.5 phosphate buffer. By rotation of a switch ing valve, the analytes were eluted from the TEC in the back-flush mode by the LC mobile phase and transferred to the analytical column, packed with o ctyl silica, The chromatographic separation was performed at 35 degrees C a nd the analytes were monitored photometrically at 295 nm. Due to the differ ences in hydrophobic character between albendazole and its metabolites, a g radient elution was applied. The mobile phase consisted of a mixture of ace tonitrile and pH 6.0 phosphate buffer. The proportion of organic modifier w as increased from 10.0 to 50.1% in 12.30 min, then from 50.1 to 66.9% in 1. 70 min. First, the gradient conditions and the temperature were optimised f or the LC separation using the DryLab software. Then, the influence of some parameters of the dialysis process on analyte recovery was investigated. F inally, the method developed was validated. The mean recoveries for albenda zole and its metabolites were about 70 and 65%, respectively. The Limits of quantification for albendazole and its metabolites were 10 and 7.5 ng/ml, respectively. (C) 2000 Elsevier Science B.V. All rights reserved.