Circadian variation in urinary excretion of ciprofloxacin after a single-dose oral administration at 1000 and 2200 hours in human subjects.

Ciprofloxacin is routinely prescribed to treat a variety of infections, including those of the urinary tract. To achieve optimum therapeutic benefits of the drug, all of the factors which influence its pharmacokinetics and effectiveness need to be determined. This study investigated the urinary excretion kinetics of ciprofloxacin upon oral administration of a single dose of 250 mg at 1000 or 2200 h in 12 healthy human subjects in a crossover design. The urine samples were analyzed for unchanged ciprofloxacin by a sensitive high-performance liquid chromatography method. A significant decrease in the rate and extent of ciprofloxacin excretion following 2200 h (109.59 versus 53.8 mg [P < 0.05]) administration was observed. This result may be due to circadian changes in the factors affecting renal excretion and also probably metabolism of ciprofloxacin.