SENSITIVE METHOD FOR THE DETERMINATION OF PHENYTOIN IN PLASMA, AND PHENYTOIN AND 5-(4-HYDROXYPHENYL)-5-PHENYLHYDANTOIN IN URINE BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

An isocratic high-performance liquid chromatographic method is described for the quantitative analysis of phenytoin (PHT) in plasma and both phenytoin and its main metabolite, 5-(4-hydroxyphenyl)-5-phenylhydantoin (p-HPPH) in urine. Following ethyl acetate (plasma) and Extrelut-1 (urine) extraction, samples are analysed by means of a reversed-phase column (Nova-Pak C18), using a mobile phase consisting of methanol-water-tetrahydrofuran (40:60:4, v/v/v) with UV detection at 230 nm. The chromatography is complete in 10 min and the results show good precision (RSD 1. 23-4.49%) and sensitivity for a linear range of 0.4-4.0 mug ml-1 for PHT in plasma, 0. 1-1.0 mug ml-1 for PHT in urine and 0. 1-1.2 mug ml-1 for p-HPPH in urine. The results indicate the method to be suitable for pharmacokinetic studies.