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Increased Bioavailability of Intravenous Versus Oral CI-1033, a Pan erbB Tyrosine Kinase Inhibitor: Results of a Phase I Pharmacokinetic Study

Authors' Affiliations: ¹ H. Lee Moffitt Cancer Center, Tampa, Florida and ² Pfizer Global Research and Development, Ann Arbor, Michigan

Requests for reprints: George R. Simon, H. Lee Moffitt Cancer Center and Research Institute, Division of Thoracic Oncology, 12902 Magnolia Drive, MRC-4W, Tampa, FL 33612. Phone: 813-972-8372; Fax: 813-979-3027; E-mail: simongr{at}moffitt.usf.edu.

Purpose: In phase I studies with oral CI-1033, dose-limiting toxicities were primarily gastrointestinal, supporting the exploration of i.v. dosing to achieve optimal drug exposures by increasing bioavailability.

Experimental Design: Fifty-three patients with advanced nonhematologic malignancies received i.v. CI-1033 via 30-minute infusions (10-500 mg) on a thrice-weekly schedule. Pharmacokinetic samples were collected on days 1 and 8 and evaluated using noncompartmental analysis.

Results: Dose levels evaluated were 10, 20, 30, 45, 67.5, 100, 150, 225, 337.5, and 500 mg. The maximum administered dose was 500 mg, whereas the maximum tolerated dose was 225 mg. The most common treatment-related grade 1 to 2 adverse events were rashes (38% of patients), nausea (17%), vomiting (17%), stomatitis (14%), and diarrhea (13%). Most common grade 3 adverse events were hypersensitivity reactions (7.5%), rashes (3.8%), and diarrhea (3.8%). No grade 4 toxicities were observed. Ten of the 53 (19%) patients had disease stabilization at their first efficacy evaluation visit (including two with minor responses). A 5- to 10-fold increase in i.v. C_max was noted with a 3-fold increase in AUC compared with oral CI-1033 at equivalent doses. Treatment-related gastrointestinal adverse events were notably less frequent with this i.v. regimen.

Conclusions: CI-1033 was safely given i.v. up to 225 mg/dose on a thrice-weekly schedule, with evidence of antitumor activity. At equivalent doses, the bioavailability of i.v. CI-1033 is thrice that of the oral formulation. Treatment with i.v. CI-1033 is feasible and may be warranted when increased drug exposures are desired.

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