Plasma protein binding rate of difloxacin in crucian carp Carassais auratus gibelio

Equilibrium dialysis was used to determine the in vitro binding rates of difloxacin(DIF) to plasma pro-teins of Carassius auratus gibelio and to investigate the effects of temperature,and of the concentrations of plasma and the drug,on the binding characteristics.The binding rate decreased from 32.4% to 19.6% as the drug concentration was raised from 0.5 μg/mL to 5 μg/mL but was unchanged between drug concentrations of 5μg/mL and 40 μg/mL.The binding rates were not affected by temperatures of 4,15,20,25,or 37℃,but the binding rate in undiluted plasma was significantly higher than in twofold(8.87±0.39)% and fourfold(4.09±0.24)% diluted plasma(P0.05).The highest combining ability(β) and dissociation constant(Kdp) were 3.5×10-7 mol/g and 4.04×10-6 mol/L,respectively.The concentration of the dissociated drug had a linear relationship with the total concentration of the drug and was given by the equation: y = 0.77x -0.18.Thus,the binding rate of DIF to plasma protein in Carassius auratus gibelio is drug concentration-dependent;it is not affected by experimental tempera-tures between 4℃ and 37℃;it is linear with concentrations of DIF between 5 μg/mL and 40 μg/mL;and it shows a nonlinear relationship between 0.5 μg/mL and 5 μg/mL.