Review of the bioavailability and pharmacokinetics of oral norfloxacin.

The pharmacokinetic profile of norfloxacin, an oral fluoroquinolone, is more complex than that of many antibacterial agents. Following administration of a 400-mg dose, peak serum concentrations of 1.5 to 2.0 micrograms/ml are achieved within one to two hours. The drug is widely distributed throughout the body, achieves high ratios of tissue to serum concentrations in both renal and prostatic tissue, and undergoes metabolic conversion. Six metabolites of norfloxacin have been identified. Approximately 30 percent of an administered dose is excreted as unchanged drug by glomerular filtration and tubular secretion. Following a single dose of norfloxacin, therapeutic levels of drug in the urine are achieved rapidly and maintained for at least 12 to 24 hours. Norfloxacin has a terminal elimination half-life of approximately three hours, although the presence of a reduced glomerular filtration rate increases the elimination half-life. Dosage modification is, therefore, necessary when the glomerular filtration rate falls below 20 ml/minute.