Pharmacokinetics of the newer fluoroquinolones

A large number of pharmacokinetic studies have been carried out using 4-quinolones in order to estimate total and renal clearance, to examine tissue penetration, to establish suitable dosage regimens and to determine the influence of kidney and liver impairment on the pharmacokinetic behaviour. Although the quinolones are poorly water soluble over the physiological pH range (6-8) they are well absorbed following oral administration. Ofloxacin is almost completely absorbed and ciprofloxacin has been shown to have an absolute bioavailability of 0.70. Plasma protein binding varies greatly from quinolone to quinolone ranging from about 10% in the case of norfloxacin to more than 90% in the case of nalidixic acid. Penetration of the quinolones into the prostate is generally good. Most quinolones, too, have been shown to penetrate blister fluid rapidly and this model has proved useful in distribution studies. Some quinolones, like ofloxacin, are excreted largely unchanged while others like pefloxacin and acrosoxacin, are almost completely metabolized. Conjugation to very water-soluble glucuronides is not common although other types of metabolites have been shown. Little information appears to have been published on the effect of liver disease on the metabolism of the quinolones. This must be an important consideration for this type of drugs which are subject to hepatic transformation. The pharmacokinetic behaviour of quinolones in patients with impaired renal function has been extensively studied. The interaction of food on the absorption does not seem to be great, there is however evidence of a drug interaction between theophylline and some of the newer quinolones. Sucralfate and antacids containing Mg2+ or (and) Al3+-ions can markedly impair the absorption of quinolone antibiotics.