PHARMACOKINETICS OF HIGH-DOSE ETOPOSIDE AFTER SHORT-TERM INFUSION

The pharmacokinetics of high-dose etoposide (total dose, 2100 mg/m2 divided into three doses given as 30-min infusions on 3 consecutive days) were studied in ten patients receiving high-dose combination chemotherapy followed by autologous bone marrow transplantation. In addition to etoposide, all subjects received 2 x 60 mg/kg cyclophosphamide and either 6 x 1,000 mg/m2 cytosine arabinoside (ara-C), 300 mg/m2 carmustine (BCNU), or 1,200 mg/m2 carboplatin. Plasma etoposide concentrations were determined by Cf-252 plasma desorption mass spectrometry. In all, 27 measurements of kinetics in 10 patients were analyzed. According to graphic analysis, the plasma concentration versus time data for all postinfusion plasma etoposide values were fitted to a biexponential equation. The mean values for the calculated pharmacokinetic parameters were: t1/2-beta, 256 +/- 38 min; mean residence time (MRT), 346 +/- 47 min; AUC, 4,972 +/- 629-mu-g min ml-1 (normalized to a dose of 100 mg/m2); volume of distribution at steady state (Vd(ss)), 6.6 +/- 1.2 l/m2; and clearance (CL), 20.4 +/- 2.4 ml min-1 m-2. A comparison of these values with standard-dose etoposide pharmacokinetics revealed that the distribution and elimination processes were not influenced by the dose over the range tested (70-700 mg/m2). Also, the coadministration of carboplatin did not lead to significant pharmacokinetic alterations. Although plasma etoposide concentrations at the time of bone marrow reinfusion (generally at 30 h after the last etoposide infusion) ranged between 0.57 and 2.39-mu-g/ml, all patients exhibited undelayed hematopoietic reconstitution.