APPARENT MICHAELIS-MENTEN KINETIC-PARAMETERS OF PHENYTOIN IN PEDIATRIC-PATIENTS

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  • 1 January 1980
    • journal article
    • research article
    • Vol. 1  (2) , 171-180
Abstract
The effects of concurrently administered anticonvulsants on Km kinetic parameters of phenytoin were investigated in 104 pediatric patients (10.5-16 yr) with seizures. Individual kinetic parameters (Km and Vmax) for phenytoin were estimated from at least 2 reliable steady-state plasma concentration and dose data. Km increased and became more variable as the number of coadministered anticonvulsants increased. Significant difference was found in a group of patients taking 3 or more coadministered anticonvulsants. Vmax was not affected by those drugs in the higher age groups. Additive inhibitory rather than inductive effects of commonly used anticonvulsants apparently caused an increase in Km. Dosage regimen adjustment of phenytoin based on the averaged Vmax in a given pediatric age group rather than the Km is recommended for a particular patient with inadequate therapeutic control of seizure or toxicity of this drug.