Journal of Pharmaceutical Sciences 1985-08-01

Altered drug-serum protein binding in the genetically obese Zucker rat.

I H Benedek, R A Blouin, P J McNamara

Index: J. Pharm. Sci. 74(8) , 837-40, (1985)

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Abstract

Drug-serum protein binding was evaluated in genetically obese Zucker rats, their lean littermates, and lean Sprague-Dawley rats. The free fraction (fp) of phenytoin was significantly higher in the obese rat (fp = 0.177) compared to its lean littermate (fp = 0.136), apparently due to displacement by free fatty acids. Conversely, diazepam and propranolol fp values were decreased in the obese Zucker rat (fp = 0.107 and fp = 0.122, respectively) compared to the lean Zucker rat (fp = 0.140 and fp = 0.174, respectively). Evidence strongly suggests that the increased binding of propranolol was not due to elevations in the serum concentrations of alpha1-acid glycoprotein (as is the case in the human obese population). Rather, the decreased fp for both diazepam and propranolol was a result of increased lipoprotein partitioning. Strain differences between the lean Zucker rat and lean Sprague-Dawley rat were also evident, with serum binding of the Sprague-Dawley rat more closely resembling the obese Zucker rat.