Phase I and pharmacokinetic studies of topotecan administered as a 72 or 120 h continuous infusion.

Topotecan (SK&F 104864-A, NSC 609699) is a water-soluble, semi-synthetic analog of camptothecin which is an inhibitor of topoisomerase I. Since topoisomerase I is cell specific for S phase, we undertook a phase I study to determine the maximum tolerated dose and toxicities of continuous infusion (CI) topotecan. This phase I trial first explored a 5 day CI every 21 day schedule. Doses of topotecan included 0.17, 0.34 and 0.68 mg/m2/day. Fourteen patients [median age 60; median performance status (PS) of 1] with refractory malignancies received 59 courses of drug. Hematologic toxicities occurred only at the highest dose level; NCI grade 3-4 granulocytopenia and thrombocytopenia occurred in 4/8 and 3/8 patients, respectively. The protocol was amended to a 3 day infusion in an effort to ameliorate toxicity and obtain greater dose intensity (DI). Doses of 0.68, 0.85, 1.05, 1.3 and 1.6 mg/m2/day were evaluated. Thirty-two patients (median age 60; median PS of 1) received a total of 115 courses. The major toxicity seen was hematologic with 9/32 and 5/32 patients demonstrating grade 3-4 granulocytopenia and thrombocytopenia, respectively. Non-hematologic toxicities were mild (grade 1-2) in the two schedules and included nausea, vomiting, fatigue and alopecia. At the maximum tolerated dose (MTD) on the 5 day schedule, patients received 0.87 mg/m2/week, whereas they received 1.08 mg/m2/week at the MTD on the 3 day schedule (24% increase in relative dose intensity). A steady-state plasma lactone concentration of 5.5 mg/ml of topotecan was achieved at the phase II recommended dose of 1.6 ng/m2/day as a 3 day continuous infusion.(ABSTRACT TRUNCATED AT 250 WORDS)