A pharmacokinetic evaluation of concomitant administration of linezolid and aztreonam

Linezolid, a new oxazolidinone antimicrobial agent, has a spectrum of activity encompassing a wide variety of Grampositive bacteria. The purpose of this study was to evaluate the pharmacokinetics of linezolid and aztreonam, an antimicrobial agent with selective activity against Gram-negative bacteria, when given alone and in combination. Healthy subjects were randomized to receive single, 30-minute intravenous infusions of (1) linezolid 375 mg, (2) aztreonam 1000 mg, and (3) linezolid 375 mg plus aztreonam 1000 mg in an open-label, crossover manner. The only statistically significant differences observed with combination treatment relative to each drug alone were an increase in the maximum plasma concentration of linezolid (approximately 18%) and an approximate 7% decrease in the apparent elimination rate of aztreonam, neither of which are expected to be clinically significant. In healthy subjects, the combination of linezolid and aztreonam was safe and well tolerated compared with each agent used alone. Pharmacokinetic data demonstrate that coadministration of linezolid and aztreonam does not alter the disposition of either agent under single-dose conditions. Therefore, it is not expected that a dose alteration of either agent will be necessary in a clinical setting.