The plasma protein binding of phenytoin was investigated in 100 epileptic patients, using equilibrium dialysis at 37 degrees C. The unbound fractions of phenytoin in plasma formed a skewed distribution, with a range of 9.7 to 24.7% and a median value of 12.3%. Most (80%) patients appeared to form one group with free phenytoin fractions from 9.7 to 14.5%, while the remainder formed a group with elevated free fractions (greater than 14.5%). Total and unbound plasma concentrations of phenytoin were strongly correlated (r=0.95, P less than 0.0001). There was a weak correlation between increasing age and the unbound phenytoin fraction (r=0.28, P less than 0.01). The results indicate that measurement of the total phenytoin concentration in plasma should usually provide a reliable index of anticonvulsant effect. However, determination of the unbound phenytoin fraction would be beneficial in the management of those patients in whom this fraction may be elevated, due to interacting drugs or biochemical abnormalities.

Item Type:	Refereed Article
Research Division:	Biomedical and Clinical Sciences
Research Group:	Pharmacology and pharmaceutical sciences
Research Field:	Clinical pharmacology and therapeutics
Objective Division:	Health
Objective Group:	Evaluation of health and support services
Objective Field:	Evaluation of health and support services not elsewhere classified
UTAS Author:	Peterson, GM (Professor Gregory Peterson)
UTAS Author:	McLean, S (Professor Stuart McLean)
UTAS Author:	Aldous, S (Dr Stephen Aldous)
UTAS Author:	von Witt, RJ (Dr Richard von Witt)
ID Code:	111034
Year Published:	1982
Web of Science® Times Cited:	49
Deposited By:	College Office - CHM
Deposited On:	2016-08-26
Last Modified:	2016-08-26
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