SIMULTANEOUS DETERMINATION OF THE LACTONE AND CARBOXYLATE FORMS OF 7-ETHYL-10-HYDROXYCAMPTOTHECIN (SN-38), THE ACTIVE METABOLITE OF IRINOTECAN (CPT-11), IN RAT PLASMA BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

We established a high performance liquid chromatography (HPLC) method for the simultaneous determination of the lactone and carboxylate form s of 7-ethyl-10-hydroxycamptothecin (SN-38), the active metabolite of the antitumor drug irinotecan (CPT-11), in rat plasma. Plasma samples were pretreated with chilled MeOH and zinc sulfate to precipitate prot ein, and were then directly injected into the HPLC system. Chromatogra phy was carried out with a Puresil C18 column (particle size 5 mu M), and the mobile phase consisted of 0.1 M ammonium acetate buffer (pH 5. 5) and acetonitrile (70/30, v/v) containing 20 mM of tetra-n-pentylamm onium bromide. The column effluent was monitored with a spectrofluorom eter (excitation wavelength 380 mn, emission wavelength 540 nm). The m ethod was valid for SN-38 lactone (5-2500 ng/ml) and carboxylate (5-10 00 ng/ml).