Biomaterial Database

Population pharmacokinetics of phenytoin from routine clinical data in Japan: an update. 1990

E Yukawa, and S Higuchi, and T Aoyama

Department of Hospital Pharmacy, Faculty of Medicine, Kyushu University, Fukuoka, Japan.

Routine clinical pharmacokinetic data collected from outpatients receiving phenytoin (PHT) were reanalyzed to estimate population pharmacokinetic parameters. There were 756 steady-state PHT concentrations and associated dosage rates (mg/d) from 334 outpatients. The data were analysed using nonlinear mixed effects model (NONMEM), a computer program designed for population pharmacokinetic analysis that allows pooling of data from many individuals. The influence of weight, co-anticonvulsants on the maximum elimination rate (Vm) and age, co-anticonvulsants on the Michaelis-Menten constant (Km) and the influence of dosage form on the bioavailability (F) of PHT were investigated. The Vm and Km of a 60 kg adult outpatient treated with PHT alone were estimated to be 325 mg/d and 2.41 micrograms/ml, respectively, while for a same size individual taking PHT with co-anticonvulsants respective estimates were 351 mg/d and 3.18 micrograms/ml. The parameter of a power function of weight was estimated to adjust Vm for body size. The best function adjusts Vm in proportion to weight to the 0.737 power. The Km for patients less than 15 years old was 24.8% less than that of adults. Assuming the F of PHT to be 1 in patients prescribed a tablet, the F value in patients prescribed a powder was [1-exp(-9.92/Dij)]; Dij is the daily dose of PHT for the ith Cpss in the jth patients (mg/kg/d).

UI	MeSH Term	Description	Entries
D007223	Infant	A child between 1 and 23 months of age.	Infants
D007564	Japan	A country in eastern Asia, island chain between the North Pacific Ocean and the Sea of Japan, east of the Korean Peninsula. The capital is Tokyo.	Bonin Islands
D008297	Male		Males
D008875	Middle Aged	An adult aged 45 - 64 years.	Middle Age
D010672	Phenytoin	An anticonvulsant that is used to treat a wide variety of seizures. It is also an anti-arrhythmic and a muscle relaxant. The mechanism of therapeutic action is not clear, although several cellular actions have been described including effects on ion channels, active transport, and general membrane stabilization. The mechanism of its muscle relaxant effect appears to involve a reduction in the sensitivity of muscle spindles to stretch. Phenytoin has been proposed for several other therapeutic uses, but its use has been limited by its many adverse effects and interactions with other drugs.	Diphenylhydantoin,Fenitoin,Phenhydan,5,5-Diphenylhydantoin,5,5-diphenylimidazolidine-2,4-dione,Antisacer,Difenin,Dihydan,Dilantin,Epamin,Epanutin,Hydantol,Phenytoin Sodium,Sodium Diphenylhydantoinate,Diphenylhydantoinate, Sodium
D012016	Reference Values	The range or frequency distribution of a measurement in a population (of organisms, organs or things) that has not been selected for the presence of disease or abnormality.	Normal Range,Normal Values,Reference Ranges,Normal Ranges,Normal Value,Range, Normal,Range, Reference,Ranges, Normal,Ranges, Reference,Reference Range,Reference Value,Value, Normal,Value, Reference,Values, Normal,Values, Reference
D002648	Child	A person 6 to 12 years of age. An individual 2 to 5 years old is CHILD, PRESCHOOL.	Children
D002675	Child, Preschool	A child between the ages of 2 and 5.	Children, Preschool,Preschool Child,Preschool Children
D005260	Female		Females
D006801	Humans	Members of the species Homo sapiens.	Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man