Biopharmaceutics & Drug Disposition 2008-07-01

Estimation of serum protein binding of compounds metabolized in serum using matrix inhibition.

Takahide Uchimura, Motohiro Kato, Rie Shiokawa, Yoshiaki Nabuchi, Kimitoshi Saito, Haruki Kinoshita

Index: Biopharm. Drug Dispos. 29(5) , 308-10, (2008)

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Abstract

It is difficult to evaluate the serum protein binding of compounds that are metabolized in rat serum, even when using ultrafiltration. Protein binding was estimated using matrix inhibition, a method that uses the change in metabolic velocity achieved by changing the free fraction of a compound in the incubation mixture by diluting the serum with phosphate buffered saline. The T(1/2) of phenyl nicotinate, benzyl nicotinate, octyl nicotinate, hexyl nicotinate, butyl nicotinate and [(3)H] compound A were 0.165, 0.780, 2.62, 3.94, 5.22 and 135 min, respectively, with protein binding values of 82.1%, 91.6%, 98.8%, 98.5%, 85.5% and 96.9%. The protein binding value of compound A estimated by ultrafiltration was 93.4%, indicating that the two methods give similar values. The matrix inhibition method is thus applicable for the evaluation of compounds metabolized in serum, and provides a simple, useful method to determine protein binding.