Phase I studies on chlorozotocin

A phase I investigation of chlorozotocin, a new‐water soluble chloroethylnitrosourea, was undertaken to define its pharmacologic effects in man. Forty‐three patients received single intravenous doses ranging from 5 to 175 mg/m 2 every 6 wk. No signs of toxicity were observed at doses of under 120 mg/m 2 , but thrombocytopenia occurred at higher doses. The thrombocytopenic nadir appeared to be dose‐dependent and occurred 4 wk after treatment. Platelet transfusions were required in 2 patients who had previously received intensive chemotherapy. No significant leukopenia occurred. A mild reversible and delayed elevation of hepatic transaminases was found in 25% of courses of 120 mg/m 2 or more. No renal toxicity was observed and gastrointestinal toxicity was mild. Investigation of clinical pharmacology revealed a rapid triphasic plasma clearance with initial t ½ s of 3, 15, and 30 min. The concentration of N‐nitroso intact drug at 1 hr was 10% of the initial peak level. Renal excretion accounted for half of the dose. No significant concentration of N‐nitroso intact or radiolabeled drug was detected in the cerebrospinal fluid of 2 patients in whom it was examined. There were objective signs of therapeutic activity in 5 patients, 3 of whom had melanoma. Based on these studies, the recommended dose for phase II investigation of chlorozotocin is 120 mg/m 2 every 6 wk.