Clinical pharmacokinetics of the newer antibacterial 4-quinolones

Structural modification of the so-called 'first-generation' or 'urinary' quinolones has led to a considerable increase in their intrinsic antibacterial activity, together with marked changes in the pharmacokinetic properties. Tissue penetration is the most notable change, and the newer quinolones are comparable with the newer broad spectrum beta-lactams in their clinical spectrum of activity. Marketed compounds in the 4-quinolones group include pefloxacin, ofloxacin, enoxacin, ciprofloxacin and norfloxacin; many more compounds are in various stages of research and development. The 4-quinolones act by inhibition of bacterial DNA gyrase, a process which is pH and concentration dependent. The bactericidal activity can be partly abolished if protein synthesis is inhibited by chloramphenicol, or if RNA synthesis is inhibited by rifampicin (rifampin). The antibacterial spectrum of activity includes methicillin- and gentamicin-resistant staphylococci, multiresistant non-fermenters, all Enterobacteriaceae, Legionella, Neisseria species, Branhamella and Haemophilus influenzae. With the exception of norfloxacin, which is only 30 to 40% bioavailable from the oral route, the 4-quinolones are 80 to 100% bioavailable, absorption occurring within 1 to 3 hours. Food does not significantly alter Cmax, AUC or elimination half-life, although tmax, may be increased. The 4-quinolones are widely distributed throughout the body, with volumes of distribution greater than 1.5 L/kg. Protein binding is less than 30% in most cases. Penetration into most tissues is good. With the exception of ofloxacin and lomefloxacin (NY 198), which are metabolically stable, metabolism of the 4-quinolones occurs primarily at the C7 position in the piperazinyl ring. Biotransformation is extensive (85%) with pefloxacin, medium (25 to 40%) with ciprofloxacin and enoxacin, and low (less than 20%) with norfloxacin. Elimination half-lives vary between 3 and 5 hours (ciprofloxacin) and 8 to 14 hours (pefloxacin). Biliary concentrations of the 4-quinolones are 2 to 10 times greater than those in serum or plasma, with several compounds undergoing enterohepatic circulation. There is some evidence that ciprofloxacin, norfloxacin, ofloxacin and enoxacin have an active renal tubular excretion pathway. In impaired renal function, reduction of the glomerular filtration rate below 30 ml/min (1.8 L/h) is associated with an increase in elimination half-life and AUC, and a decrease in renal and total clearance of the 4-quinolones, and a decrease in 24-hour urinary recovery.(ABSTRACT TRUNCATED AT 400 WORDS)