Purpose: The purpose of this study is to investigate the influence of changes in the human serum albumin (HSA) and free fatty acid (FFA) on alteration of the binding abilities of sites I and II after the operation of an artificial heart-lung machine. Methods: The binding abilities of phenytoin (site I) and diazepam (site II) to patients' sera collected before and after the operation of an artificial heart-lung machine and pseudopatient serum samples were examined by ultra-filtration. Results: The binding ability of site I markedly decreased after the operation of an artificial heart-lung machine in all patients, and the binding ability of site II unexpectedly increased in some patients. The variation in pseudopatient serum was similar to that in the patient sera. Conclusions: The difference in the binding ability between sites I and II was due to that the fact that the binding ability of site I is more strongly influenced by HSA level reduction than by [FFA]/[HSA] reduction, whereas the binding ability of site II is more strongly influenced by [FFA]/[HSA] reduction than by HSA level reduction in some patients. Therefore, it may be possible to predict the binding ability of site I by monitoring the HSA level without directly monitoring the free phenytoin fraction (%).
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