Pharmacokinetics and Pharmacodynamics of the New Quinolones

In this review, the authors describe the pharmacokinetic (PK) and pharmacodynamic (PD) characteristics of the new quinolones (levofloxacin, gatifloxacin, moxifloxacin, gemifloxacin, and garenoxacin) and discuss their implications on adequate therapy of patients with respiratory infections. The newer quinolones display excellent bioavailability and have longer serum half-lives than ciprofloxacin. In addition, they have the ability to concentrate in respiratory tract tissues and fluids at levels that exceed serum-drug concentrations. Also, the newer quinolones exhibit broad-spectrum activity against both susceptible and resistant organisms. Those favorable PK/PD properties make the new quinolones an attractive therapeutic alternative to traditional agents for common respiratory infections. Understanding the PK/PD of quinolone antibiotics can facilitate selection of optimal regimens to hasten response, prevent treatment failures, and minimize the development of resistance.

Pharmacokinetics and pharmacodynamics of fluoroquinolones

The pharmacokinetic characteristics of levofloxacin, moxifloxacin, and gatifloxacin include excellent oral bioavailability (90-99%), extensive penetration into tissues and body fluids, and an elimination half-life (6-12 hrs) that allows for once-daily dosing in patients with normal renal function. Levofloxacin and gatifloxacin primarily are excreted unchanged in the urine, whereas moxifloxacin undergoes hepatic metabolism. The pharmacodynamic values that correlate with successful clinical and microbiologic outcomes, as well as prevent emergence of bacterial resistance, are ratios of maximum or peak unbound drug concentration (Cmax) to minimum inhibitory concentration (MIC), and 24-hour unbound area under the concentration curve (AUC(0-24hr)) to MIC. For gram-negative infections, a Cmax:MIC greater than or equal to 10 and AUC(0-24hr):MIC greater than or equal to 125 are associated with increased probability of a successful outcome. For infections caused by Streptococcus pneumoniae, an AUC(0-24hr):MIC of 30 or more is suggested for favorable clinical outcomes. Pharmacokinetic and pharmacodynamic values influence rational therapeutic decisions in the selection and dosages of these drugs.