The clinical pharmacokinetics of levofloxacin

Levofloxacin is a fluoroquinolone antibiotic and is the optical S-(-) isomer of the racemic drug substance ofloxacin. It has a broad spectrum of in vitro activity against Gram-positive and Gram-negative bacteria, as well as certain other pathogens such as Mycoplasma, Chlamydia, Legionella and Mycobacteria spp. Levofloxacin is significantly more active against bacterial pathogens than R-(+)-ofloxacin. Levofloxacin hemihydrate, the commercially formulated product, is 97.6% levofloxacin by weight. Levofloxacin pharmacokinetics are described by a linear 2-compartment open model with first-order elimination. Plasma concentrations in healthy volunteers reach a mean peak drug plasma concentration (Cmax) of approximately 2.8 and 5.2 mg/L within 1 to 2 hours after oral administration of levofloxacin 250 and 500mg tablets, respectively. The bioavailability of oral levofloxacin approaches 100% and is little affected by the administration with food. Oral absorption is very rapid and complete, with little difference in the serum concentration-time profiles following 500mg oral or intravenous (infused over 60 minutes) doses. Single oral doses of levofloxacin 50 to 1000mg produce a mean Cmax and area under the concentration-time curve (AUC) ranging from approximately 0.6 to 9.4 mg/L and 4.7 to 108 mg.h/L, respectively, both increasing linearly in a dose-proportional fashion. The pharmacokinetics of levofloxacin are similar during multiple-dose regimens to those following single doses. Levofloxacin is widely distributed throughout the body, with a mean volume of distribution of 1.1 L/kg, and penetrates well into most body tissues and fluids. Drug concentrations in tissues and fluids are generally greater than those observed in plasma, but penetration into the cerebrospinal fluid is relatively poor (concentrations approximately 16% of simultaneous plasma values). Levofloxacin is approximately 24 to 38% bound to serum plasma proteins (primarily albumin); serum protein binding is independent of serum drug concentrations. The plasma elimination half-life (t1/2 beta) ranges from 6 to 8 hours in individuals with normal renal function. Approximately 80% of levofloxacin is eliminated as unchanged drug in the urine through glomerular filtration and tubular secretion; minimal metabolism occurs with the formation of no metabolites possessing relevant pharmacological activity. Renal clearance and total body clearance are highly correlated with creatinine clearance (CLCR), and dosage adjustments are required in patients with significant renal dysfunction. Levofloxacin pharmacokinetics are not appreciably affected by age, gender or race when differences in renal function, and body mass and composition are taken into account. Important drug interactions exist with aluminium- and magnesium-containing antacids and ferrous sulfate, as with other fluoroquinolones, resulting in significantly decreased levofloxacin absorption when administered concurrently. These agents should be administered at least 2 hours before or after levofloxacin administration. Cimetidine and probenecid decrease levofloxacin renal clearance and increase t1/2 beta; the magnitudes of these interactions are not clinically significant. Levofloxacin appears to have only minor potential for significantly altering the pharmacokinetics of theophylline, warfarin, zidovudine, ranitidine, digoxin or cyclosporin; however, patients receiving these drugs concurrently should be monitored closely for signs of enhanced pharmacological effect or toxicity. Levofloxacin pharmacokinetics are not significantly altered by sucralfate when administration of these drugs is separated by at least 2 hours.