Following a single oral administration of ciprofloxacin, norfloxacin, pefloxacin and ofloxacin preparations to healthy volunteers simultaneously collected, saliva and plasma 4-fluoroquinolone concentrations were assayed by HPLC. Pharmacokinetic properties were determined by ordinary least squares fitting of the two compartment pharmacokinetic model to the experimental data. A good correlation between plasma and saliva data has been demonstrated. The saliva to venous plasma drug concentration ratio S/P appeared to be time-dependent in the case of norfloxacin and pefloxacin. It was demonstrated that S/P is a function of the quotient of the rate of absorption and venous plasma drug concentration. The calculated S/P ratios with the influence of absorption eliminated, (S/P) corr are: ciprofloxacin 0.53 90.02, norfloxacin 0.34 9 0.04, ofloxacin 0.43 90.02 and pefloxacin 0.39 9 0.02 (mean 9 S.E.). These values are apparently independent of log D thus making it impossible to predict S/P on the basis of partition principles. The corresponding (S/P) dif ratios were calculated on the basis of the assumption that an equilibrium is established across the blood -saliva barrier, which is permeable only for nonionized and nonprotein bound drug fraction. Comparing (S/P) corr with the calculated (S/P) dif ratios it is evident that 4-fluoroquinolone permeation in saliva cannot be described by passive diffusion based on pH-partition theory.
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