title: Genetic differences in phenytoin pharmacokinetics. In vivo clearance and in vitro metabolism among inbred strains of mice.
abstract: Plasma phenytoin elimination rates were examined among twelve inbred strains of mice. Two populations are identified--the 'fast metabolizers' (BALB/cN, C57BL/6N, C57BL/6J, AKR/N, AKR/J and C3H/HeN) having almost exactly twice as rapid an elimination rate as the 'slow metabolizers' (CL/FR, CBA/J, DBA/2N, STAR/N, SJL/N, DBA/2J and RF/N). The difference in elimination rate between C57BL/6J and DBA/2J cannot be accounted for by dissimilarities in volume of distribution. The phenytoin elimination rate in the (C57BL/6J)(DBA/2J)F1 heterozygote is expressed as an additive trait. A good correlation exists between phenytoin elimination rates in vivo and phenytoin metabolism by liver microsomes in vitro, as determined by a newly described assay using high-performance liquid chromatography. 3-Methylcholanthrene pretreatment does not enhance phenytoin elimination or metabolism. The cytochrome P-450-mediated monoxygenase metabolism of phenytoin is not associated with the Ah locus or with coat color among progeny of the (C57BL/6N)(DBA/2N) F1 x DBA/2N backcross. Phenobarbital pretreatment enhances phenytoin elimination and metabolism in both a fast metabolizer (C57BL/6N) and a slow metabolizer (DBA/2N) strain. Phenobarbital pretreatment probably also induces non-P-450 enzymes, such as those which form the phenytoin dihydrodiol and the glucuronide and glutathione conjugates, in addition to inducing one or more forms of P-450 that oxygenate phenytoin. These data probably reflect allelic differences in a structural gene encoding for one (or more) form(s) of control cytochrome P-450 that metabolizes phenytoin, rather than allelic differences in a regulatory gene. The marked sensitivity of inbred mouse strains CL/FR and A/J and the marked resistance of STAR/N, Swiss-Webster, and C57BL/6 to phenytoin-induced cleft lip and/or palate cannot be explained by genetic differences in phenytoin elimination rates or liver microsomal metabolism in vitro, as measured by the methods described in this report.
mesh_terms: D000818:Animals; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics; D006207:Half-Life; D066298:In Vitro Techniques; D007206:Individuality; D007700:Kinetics; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D008862:Microsomes, Liver / Q000378:metabolism; D010672:Phenytoin / Q000378:metabolism*; D012737:Sex Factors; D013045:Species Specificity
chemical_list: D010672:Phenytoin; D003577:Cytochrome P-450 Enzyme System