Pharmacokinetics of high-dose VP-16: 6-hour infusion versus 34-hour infusion.

VP-16 was administered in high doses (30-45 mg/kg) in combination with busulfan (BU) and cyclophosphamide (CY). The anticancer activity of VP-16 is thought to be schedule-dependent. We investigated a 6-h and a 34-h infusion of VP-16 to compare pharmacokinetic parameters and toxicity. Blood samples were taken from a total of 16 patients during infusion time (6 h and 34 h, respectively) and thereafter up to 2 days after bone marrow transplantation (BMT). VP-16 concentrations were measured in all plasma samples with HPLC technique and electrochemical detection and the results were analyzed with a pharmacokinetic data analysis system. All calculated pharmacokinetic parameters in the two patient groups were essentially similar. There were no statistically significant differences in half-lives, mean residence time, volume of distribution, total clearance and area under the curve. The treatment-related toxicity was not different between groups. The major difference was the maximal concentration in the case of 6-h infusions (122 +/- 35 micrograms/ml) and in the case of 34-h infusions (23.2 +/- 4.9 micrograms/ml) and the duration of VP-16 concentrations with > 10 and > 1 microgram/ml. Drug levels above these thresholds were always longer in case of 34-h infusions. In 8 of 16 patients VP-16 concentrations were measured in plasma samples at the time of BMT ranging from 80 to 820 ng/ml. The two different schedules for VP-16 administration, either given as a 6-h infusion or as a 34-h infusion, are bioequivalent in pharmacokinetic terms.(ABSTRACT TRUNCATED AT 250 WORDS)