PHARMACOKINETICS OF RECOMBINANT HUMAN INTERLEUKIN-3 ADMINISTERED SUBCUTANEOUSLY AND BY CONTINUOUS INTRAVENOUS-INFUSION IN PATIENTS AFTER CHEMOTHERAPY FOR OVARIAN-CANCER

Twenty chemotherapy-naive patients with ovarian carcinoma received 1, 5, 10, or 15 mug/day (rive patients per dose step) of recombinant huma n interleukin 3 (rhIL-3) over 7 days after carboplatin/cyclophosphamid e in Cycles 1 and 3. Patients received rhIL-3 by continuous i.v. infus ion or once daily s.c. injection in Cycle 1 and the alternate route in Cycle 3. Plasma rhIL-3 samples were obtained once daily on Days 1 to 6 and serially over a 24-h per-iod on Day 7 for pharmacokinetic assess ment of s.c. and i.v. administered rhIL-3 in 16 and 17 patients, respe ctively. Concentrations were assayed by a time-resolved fluorescence s andwich immunoassay. Pharmacokinetic parameters were derived by noncom partmental methods. Mean steady-state concentrations during continuous i.v. infusion ranged from 117 pg/ml (1 mug/kg/day) to 2217 pg/ml (15 mug/kg/day) and were linearly related to dose (r = 0.87, P < 0.001). W hen dose normalized, the mean steady-state concentrations were compara ble at all doses. The total-body clearance was approximately 4 to 5 ml /min/kg. Elimination half-life (t1/2i.v.) could be assessed for the 5- to 15-mug/kg/day dose levels and was 53, 41, and 26 min for the 5-, 1 0-, and 15-mug dose levels, respectively (not significant between dose levels). Following s.c. injection, the maximum rhIL-3 plasma concentr ation ranged from 206 pg/ml (1 mug/kg/day) to 6930 pg/ml (15 mug/day). Both the maximum measured plasma concentration (r = 0.89, P < 0.0001) and the area under the plasma concentration/time curve (r = 0.93, P < 0.0001) were related to dose. Dose-normalized values were comparable over the entire dose range. Elimination t1/2s.c was 4.8 h at the 1-mug dose level and roughly half this time for the 5- to 15-mug/kg/day dos e levels. The systemic clearance of approximately 5 to 6 ml/min/kg was comparable at all dose levels. Based on trough levels of the 7-day s. c. course, no rhIL-3 accumulation occurred. Bioavailability of s.c. ad ministered rhIL-3 was nearly 100%. No correlation between creatinine c learance and pharmacokinetic parameters of rhIL-3 could be demonstrate d. Since there was also no difference in hematological efficacy betwee n the two routes of rhIL-3 administration, we conclude that the s.c. r oute of administration appears to have no disadvantages over the i.v. route and may facilitate its clinical application.