In vitro and in vivo ciprofloxacin pharmacokinetics in human neutrophils.

Early in vitro investigations have shown that ciprofloxacin is concentrated within human neutrophils (polymorphonuclear leukocytes [PMNs]) at between 3 and 11 times the extracellular concentration. The elution of ciprofloxacin from cells is relatively rapid when the extracellular concentration is reduced. In order to estimate the in vivo intracellular penetration of ciprofloxacin and to determine its intracellular pharmacokinetics, PMNs were recovered from blood samples drawn from healthy volunteers at different times during a 24-h period after they were given a 750-mg oral dose. High-performance liquid chromatographic determination of ciprofloxacin in serum and cells showed that the intracellular/serum ratio was 3.7 at 1.5 h (maximum concentration of drug in serum), 5.7 at 12 h, and 20 at 24 h. The area under the curve ratio was 3.73. The mean elimination half-lives of ciprofloxacin were 3.7 and 6.2 h in serum and PMNs, respectively. These data show that in vivo findings are in agreement with in vitro findings. The large uptake of ciprofloxacin by PMNs combined with a prolonged intracellular half-life described under the conditions of human therapy should provide the basis for the use of ciprofloxacin in infections caused by susceptible intracellular bacteria.