Specific high-performance liquid chromatography assay for determination ofrifabutin plasma concentration following Extrelut column extraction

A specific, precise and accurate assay for determination of rifabutin in hu man plasma using Extrelut column extraction was developed and validated. Ri fabutin concentrations were calculated with a standard curve ranging from 5 to 800 ng ml(-1), using a split-curve approach. Chromatographic peaks were separated by means of a 5 mu m Symmetry Shield RP8 using a KH2PO4 (0.05 M) buffer-acetonitrile mobile phase. Detection wavelength was set at 275 nm. Chromatography was carried out at room temperature (20-25 degrees C). The l imit of quantification was 5 ng ml(-1). The recovery was over 71%. The intr a-day precision of the assay was 5, 7, and 1% while the inter-day precision was 11.2, 8.1, and 5.8% at concentrations of 30, 150 and 500 ng ml(-1), re spectively. The accuracy ranged from 99 to 108%. Forty of the drugs most co mmonly administered to HIV-positive patients were found not to interfere wi th the assay. The assay has been used in a comparative study of rifabutin p harmacokinetics in HIV-positive patients with or without wasting syndrome. (C) 1999 Elsevier Science B.V. All rights reserved.