Purpose: To define the maximum-tolerated dose, recommended phase II dose (RD), dose-limiting toxicity (DLT), and pharmacokinetics of a novel taxane, RPR 109881A, administered on days 1 and 8 of a 21-day cycle.
Patients and methods: Twenty-nine patients were enrolled and treated according to a modified continual reassessment method from a starting dose of 7.5 mg/m(2) to 52.5 mg/m(2). Detailed pharmacokinetic analyses of blood and urine were performed on days 1 and 8 of the first cycle. Toxicity was monitored weekly.
Results: DLT consisting of grade 3 or 4 diarrhea was seen in three of six patients at 52.5 mg/m(2). Grade 3 or 4 granulocytopenia was also seen in five of six patients treated at this dose (four of six in the first cycle). At the next lower dose level, 45 mg/m(2) toxicity was moderate, with only one of 12 patients experiencing severe diarrhea and grade 4 granulocytopenia with associated infection. Drug concentrations were consistent with a three-compartment open model. The total-body clearance suggests a linear dose-concentration relationship. RPR 109881A has a high clearance (mean, 42.6 L/h/m(2)), a large volume of distribution (mean, 952 L/m(2)), and a long terminal half-life (mean, 24 hours). There was no drug accumulation between days 1 and 8. One partial response was seen in a patient with renal cell carcinoma.
Conclusion: The RD of RPR 109881A given as a 1-hour infusion on days 1 and 8 of a 21-day cycle is 45 mg/m(2). At this dose the drug is well tolerated and should be further studied.