Relationship between protein binding of bilirubin, salicylic acid, and sulfisoxazole in serum of unmedicated and phenobarbital-treated rats.

The relationship between the protein binding of bilirubin, salicylic acid, and sulfisoxazole in the serum of phenobarbital-treated and untreated rats was studied. The free fraction of bilirubin in serum varied about threefold between animals but was not related to the albumin concentration, the free fraction of salicylate, or the free fraction of sulfisoxazole. However, there was a strong positive correlation between the free fraction values of salicylate and sulfisoxazole. The free fraction value for each of these drugs showed a significant negative correlation with the serum albumin concentration. Treatment of the animals with phenobarbital had no apparent effect on the serum protein binding of bilirubin, salicylic acid, and sulfisoxazole.