SIMULTANEOUS DETERMINATION OF THE LACTONE AND CARBOXYLATE FORMS OF THE CAMPTOTHECIN DERIVATIVE CPT-11 AND ITS METABOLITE SN-38 IN PLASMA BYHIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

CPT-11 (irinotecan) and mainly its metabolite SN-38 are potent antitum or derivatives of camptothecin. As the active lactone forms of both CP T-11 and SN-38 exist in ps-dependent equilibrium with their respective less potent open-ring hydroxy acid species, the simultaneous monitori ng of both forms of both compounds is relevant. CPT-11 and SN-38 deriv atives have quite different fluorescence responses. In order to avoid any compromise on the wavelength setting, we developed chromatographic conditions allowing simple automated wavelength setting changes which have been prevented using existing methods involving conventional C-1 8 columns. This was achieved by means of a Symmetry C-18 column combin ed to a gradient elution program using acetonitrile and 75 mM ammonium acetate plus 7.5 mM tetrabutylammonium bromide at pH 6.4. The develop ed conditions allowed an elution order suitable for a simple automated wavelength change in respect to reliable peak integration. CPT-11 and SN-38 derivatives were detected at lambda(ex) = 362 nm/lambda(em) = 4 25 nm and lambda(ex) = 375 nm/lambda(em) = 560 nn, respectively. The d eveloped method allowed the detection of amounts less than 3 pg of eac h derivative injected on column. The method was successfully applied t o pharmacokinetic and toxicokinetic studies in rat and dog. (C) 1998 E lsevier Science BN. All rights reserved.