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The Pharmacokinetics of Linezolid Are Not Affected by Concomitant Intake of the Antioxidant Vitamins C and E

From Clinical Pharmacology, Pharmacia, Singapore (Dr. Gordi, Ms. Hong); Pharmacia Clinical Research Unit, Singapore General Hospital (Dr. Tan); and Clinical Pharmacology (Ms. Hopkins, Dr. Antal), Clinical Biostatistics (Dr. Francom), and Global Drug Metabolism (Dr. Slatter), Pharmacia, Kalamazoo, Michigan. Dr. Gordi's current affiliation is the Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, State University of New York at Buffalo.

In vitro metabolism experiments have suggested a possible role for endogenous reactive oxygen species (ROS) in the in vivo clearance of linezolid, a synthetic antibiotic of the oxazolidinone class. This observation has resulted in the hypothesis that dietary antioxidant supplements might disturb the balance of ROS in vivo and thereby lower the clearance of linezolid. The purpose of this open-label, two-group parallel design study was to investigate whether continuous intake of widely used vitamin C or vitamin E will affect the pharmacokinetics of linezolid. A total of 28 healthy volunteers (27 male and 1 female), including 22 of Chinese origin, were administered a single oral dose of 600 mg linezolid on days 1 and 8. Half of the subjects received daily oral doses of 1000 mg vitamin C on days 2 through 9, whereas the other half were administered daily oral doses of 800 IU vitamin E during the same time period. Serial blood samples for assessment of the pharmacokinetic parameters of linezolid and its two inactive metabolites were collected on days 1 and 8, whereas vitamin concentrations were measured prior to and after the vitamin intake on these days. Urine was collected on days 1 and 8 to assess the fraction of dose excreted as linezolid and its major metabolites. All linezolid samples were analyzed according to validated HPLC/MS/MS methods. Linezolid was well tolerated in both groups with no reported clinically significant adverse events. No significant changes were found between the day 1 and day 8 AUC_0- and C_max values of linezolid in either the vitamin C treatment group (p = 0.55 and p = 0.64, respectively) or the vitamin E treatment group (p = 0.06 and p = 0.49, respectively). Assessment of other pharmacokinetic parameters did not imply any change across the study groups. In conclusion, linezolid pharmacokinetics are not affected by concomitant administration with vitamins C and E. Therefore, no dose adjustment is necessary in patients taking vitamin C or vitamin E. These no-effect drug interaction data are in accord with current literature indicating that antioxidant vitamins have only subtle effects on overall ROS balance in vivo.

Key Words: Linezolid • pharmacokinetics • vitamins C and E • drug interactions

Address for reprints: Edward J. Antal, PhD, Pharmacia, 301 Henrietta Street, Kalamazoo, MI 49001.

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