LIQUID-CHROMATOGRAPHIC METHOD FOR SIMULTANEOUS DETERMINATION OF PHENYTOIN AND 5-(4-HYDROXYPHENYL)-5-PHENYLHYDANTOIN IN PLASMA AND URINE

  • 1 January 1980
    • journal article
    • research article
    • Vol. 26  (7) , 835-839
Abstract
A liquid-chromatographic assay for the central depressant phenytoin and its p-hydroxylated metabolite, 5-(4-hydroxyphenyl)-5-phenylhydantoin, in [human] plasma and urine is described. Unlike previously reported methods, this procedure is sensitive enough to allow quantitation of the unconjugated metabolite in plasma at concentrations observed clinically (50-500 .mu.g/l). Simultaneous measurements of the drug and its metabolite in plasma and urine may be helpful in explaining changes in the apparent clearance of phenytoin, and in characterizing its nonlinear disposition, which is assumed to occur through its metabolite. The method may be used without modification for analysis of phenobarbital and carbamazepine in plasma. The accuracy of the method for the 3 drugs was assessed for 25 mo. in a quality-assurance program for determining drug concentrations. Regression slopes for measured vs. reported values for phenytoin, phenobarbital and carbamazepine were 1.02, 0.99 and 0.99, respectively.

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