PATHOPHYSIOLOGY AND THERAPY OF IRINOTECAN-INDUCED DELAYED-ONSET DIARRHEA IN PATIENTS WITH ADVANCED COLORECTAL-CANCER - A PROSPECTIVE ASSESSMENT

Purpose: Irinotecan(CPT-I I),a camptothecin derivative, has shown effi cacy against colorectal cancer. Delayed-onset diarrhea is its main lim iting toxicity. The aim of this study was to determine the pathophysio logy of CPT-ll-induced delayed-onset diarrhea and assess the efficacy of combined antidiarrheal medication in a phase II, prospective, succe ssive-cohorts, open study. Patients and Methods: Twenty-eight patients with advanced colorectal cancer refractory to fluorouracil (5-FU) the rapy received CPT-11 350 mg/m(2) every 3 weeks. The first cohort of 14 consecutive patients explored for the mechanism of diarrhea received acetorphan (a new enkephalinase inhibitor) 100 mg three rimes daily; t he second 14-patient cohort received, in addition to acetorphan, loper amide 4 mg three times daily. Before treatment, and if late diarrhea o ccurred, patients underwent colon mucosal biopsies for CPT-II and tapo isomerase I levels; intestinal transit time; fecalogram; far and prote in excretion; alpha(1)-antitrypsin clearance; D-xylose test; blood lev els for vasoactive intestinal polypeptide, glucagon, gastrin, somatost atin, prostaglandin E-2 and carboxylesterase; CPT-11/SN-38 and SN-38 g lucuronide pharmacokinetics; and stool cultures. Results: Delayed-onse t diarrhea occurred during the first three treatment cycles in 23 pati ents (82%). Electrolyte fecal measurements showed a negative or small osmotic gap in nine of nine patients and an increased alpha(1)-antitry psin clearance in six of six patients. There were no modifications in stool cultures or hormonal dysfunction. Four of 11 patients (36%) with delayed-onset diarrhea in the first cohort responded to acetorphan, w hereas nine of 10 patients (90%) responded to the combination of aceto rphan and loperamide (P <.02). Conclusion: CPT-11-induced delayed-onse t diarrhea is caused by a secretory mechanism with an exudative compon ent. Early combined treatment with loperamide and acetorphan seems eff ective in controlling the diarrheal episodes. J Clin Oncol 16:2745-275 1. (C) 1998 by American Society of Clinical Oncology.