Abstract
1 The study was designed to determine the mechanism by which vigabatrin causes a fall in plasma phenytoin concentrations when added to the drug therapy of eight epileptic patients.
2 Total plasma phenytoin concentration was measured before and at intervals during 5 weeks' treatment with vigabatrin.
3 Plasma protein binding of phenytoin, the urinary ratio of phenytoin to 5-(p-hydroxyphenyl)-5-phenylhydantoin, and antipyrine clearance were measured before and at the end of treatment period.
4 Mean plasma phenytoin concentration fell significantly by 23% during the fifth week.
5 No change was found in any of the other measures.
6 Although an interaction between phenytoin and vigabatrin has been confirmed, the mechanism has not been elucidated.
Keywords: vigabatrin, phenytoin, interactions, protein binding
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