The pharmacokinetics of oral quinolones (norfloxacin, ciprofloxacin, ofloxacin).

The newer fluoro-quinolones including norfloxacin, ciprofloxacin and ofloxacin are all characterized by a good penetration into tissues and cells. In contrast to beta-lactam antibiotics, these quinolones often achieve tissue concentrations which are several times higher than concurrent serum levels. Therefore, MIC values should not be related to serum concentrations only, when possibilities for the use of quinolones in tissue infections are discussed. Following oral administration, norfloxacin and ciprofloxacin are well absorbed and the bioavailability of ofloxacin is almost 100%. Absorption is delayed but not reduced by food. Ofloxacin is mainly excreted unchanged; norfloxacin and ciprofloxacin are metabolized to some extent, but most metabolites are biologically active. Half-lives of the drugs are 3-6 hours and they may therefore be administrated twice daily. These quinolones are excreted by glomerular filtration and tubular secretion but also via faeces. Dose reduction is needed only in patients with severe reduction of kidney function. It has been suggested that when renal function is reduced an increased transintestinal passage of the quinolones may result. In the intestines the quinolones seem to be bound to faeces; anaerobes are mainly unaffected by these antibiotics.