In vivo disposition of irinotecan (CPT-11) and its metabolites in combination with the monoclonal antibody cetuximab.

Background: The present study was designed to investigate whether a combination of irinotecan and the monoclonal antibody cetuximab shows potential to modulate the pharmacokinetics of irinotecan and its metabolites.
Patients and Methods: All patients, suffering from advanced colorectal cancer, received irinotecan (350 mg/m2) every third week and cetuximab as a loading dose (400 mg/m2) on day 2, followed by a weekly maintenance dose (250 mg/m2). Plasma samples were analysed after the first (MONO) and second (CMAB) irinotecan infusions.
Results: No significant alterations in the plasma concentrations and pharmacokinetics of irinotecan and its metabolites were observed after combination with cetuximab. Only differentiation of irinotecan into lactone and carboxylate plasma concentrations resulted in a distinctly lower cmax of the active lactone in the CMAB and a significantly higherAUClast in the MONO schedule (p<0.02).
Conclusion: The results of this study indicated that cetuximab has no clinically relevant impact on the pharmacokinetics of irinotecan, its activation into SN-38, or its detoxification by beta-D-glucuronidation.