Comparative pharmacokinetics of coumarin anticoagulants XXX: Relationship between total clearance and serum protein binding of dicumarol in rats.

The effect of serum protein binding on the elimination kinetics of dicumarol was studied. The serum free fraction of dicumarol was essentially independent of concentration over a wide concentration range and ranged from 0.00015 to 0.00079 in 10 adult rats. The total clearance of dicumarol in these animals ranged from 3.93 to 14.5 ml/kg/hr. As in previous studies, there was an excellent linear correlation between the elimination rate constant for dicumarol and the fraction of dicumarol in the liver (i.e., the amount of drug in the liver divided by the amount of drug in the body). Consistent with theoretical considerations, there was a positive and apparently linear relationship between the total clearance and the serum free fraction of dicumarol. The individual serum free fraction and the fraction in liver values for dicumarol were strongly correlated. The pharmacokinetic model based on a proportional relationship between the apparent elimination rate constant and the fraction in the liver applies to dicumarol but not to warfarin and has limited utility. On the other hand, the model relating total clearance to the serum free fraction has been found to apply to dicumarol, warfarin, and other extensively plasma protein-bound drugs and can be utilized under clinical conditions.