Pharmacokinetic considerations in quinolone therapy.

It is advisable to switch patients from parenteral to oral therapy as soon as practical. High volumes of distribution, coupled with relatively low protein binding, indicate that the quinolones are widely distributed outside extracellular fluid. Interactions with aluminum- or magnesium-containing antacids may be avoided by administering the antacids at least 2 hours after quinolone dosing. Some quinolones with high bioavailability (e.g., ofloxacin) are absorbed as reliably and completely after oral administration as when given parenterally, and dosage adjustments for these agents are unnecessary after sequential therapy. Treatment strategies may differ according to the route of drug elimination, and dosage adjustments are required in patients with renal failure who receive quinolones excreted primarily by the kidneys. Theophylline interactions may be more problematic in patients given quinolones that are primarily metabolized by the liver. Quinolones, which have concentration-dependent killing and a long postantibiotic effect, should be administered in the highest tolerated dosage. A method to assess the relative antibacterial efficacy of the quinolones uses the ratio of the Cmax:MIC90 of the organism, compared with a ratio derived from the NCCLS breakpoints for susceptibility.