PHARMACODYNAMICS AND PHARMACOKINETICS OF A 72-HOUR INFUSION OF 9-AMINOCAMPTOTHECIN IN ADULT CANCER-PATIENTS

Purpose: To investigate the pharmacokinetics and pharmacodynamics of 9 -aminocamptothecin (9-AC) infused over 72 hours at doses of 5 to 74 mu g/m(2)/h. Patients and Methods: 9-AC lactone and total (lactone plus carboxylate) plasma concentrations were measured in 44 patients with s olid tumors using a high-performance liquid chromatography (HPLC) assa y, Fifteen patients underwent extended pharmacokinetic sampling to det ermine the distribution and elimination kinetics of 9-AC. Results: At steady-state, 8.7% +/- 4.7% (mean +/- SD) of the totes drug circulated in plasma as the active 9-AC lactone, Clearance of 9-AC lactone was u niform (24.5 +/- 7.3 L/h/m(2)) over the entire dose range examined; ho wever, total 9-AC clearance was nonlinear and increased at higher dose levels, In 15 patients treated at dose levels greater than or equal t o 47 mu g/m(2)/h, the volume of distribution at steady-state for 9-AC lactone was 195 +/- 114 L/m(2) and for total 9-AC if was 23.6 +/- 10.6 L/m(2). The elimination half-life was 4.47 +/- 0.53 hours for 9-AC la ctone and 8.38 +/- 2.10 hours for total 9-AC. In pharmacodynamic studi es, dose-limiting neurtropenia correlated with steady-state lactone co ncentrations (Css) (R-2 = .77) and drug dose (R-2 = .71). Conclusion: Plasma 9-AC concentrations rapidly declined to low levels following th e end of a 72-hour infusion and the mean fraction of total 9-AC circul ating in plasma as the active lactane was less than 10%. The pharmacok inetics of 9-AC may have a great impact on its clinical activity and s hould be considered in the design of future clinical trials of this to poisomerase I inhibitor.