Dosage adjustment and pharmacokinetic profile of irinotecan in cancer patients with hepatic dysfunction

Purpose: To determine the recommended dose (RD) and the pharmacokinetic profile of irinotecan and its metabolites in cancer patients with hyperbilirubinemia. Patients and Methods: Patients were assigned to four treatment groups according to their baseline total bilirubin level. Patients in group I (bilirubin within normal range) and group II (bilirubin 1.0 to 1.5 times upper limit of normal [ULN]) received a dose of 350 mg/m² every 3 weeks. Patients in groups III (bilirubin 1.51 to 3.0 times ULN) and IV (bilirubin > 3.1 times ULN) received starting doses of 175 and 100 mg/m², respectively. RDs were defined according to the dose-limiting toxicity (DLT) experienced at cycle 1. Results: Thirty-three patients including 21 gastrointestinal cancers were included. Grade 4 febrile neutropenia and diarrhea were common DLTs in patients with hyperbilirubinemia. At a dose of irinotecan 350 mg/m², DLTs were observed in two of seven and one of five patients in groups I and II, respectively. In group III, escalated doses of irinotecan 175, 200, and 240 mg/m² were associated with DLTs in one of seven, one of five, and three of six patients, respectively. No DLT was observed in group IV. High bilirubin and alkaline phosphatase levels were associated with an exponential decrease in the clearance of irinotecan. Pharmacokinetic analysis showed that the relative increase in exposure was likely caused by reduced biliary excretion. Conclusion: We showed that baseline total bilirubin level could be used to determine the appropriate dose of irinotecan in cancer patients with hepatic dysfunction. Doses of 350 mg/m² and 200 mg/m² were considered RDs in patients with bilirubin values ≤ 1.5 times ULN and 1.51 to 3.0 times ULN, respectively.