Risk of the Interpretation of Phenytoin Plasma Levels in the Intensive Care – Case Report

Overview

Phenytoin is a commonly prescribed antiepileptic drug in medical practice. As it is a drug which has a non-linear saturable pharmacokinetics,a relatively narrow therapeutic range and a large number of reported pharmacokinetic interactions, plasma phenytoin concentration is inevitable tomonitor. Our aim is to emphasize, one of serious interactions of phenytoin with enteral feeding formulas administered together with phenytoin bynasogastric tube. This interaction decreases bioavailability of phenytoin resulting often in detection of subtherapeutic concentrations, thoughrecommended daily doses (recommended daily dose 5–7 mg/kg/day, RDD 300 mg) are administered. In our article, we refer the case of an elderly manadmitted to the intensive care unit. Patient’s phenytoin serum concentrations dramatically decreased during simultaneous administration of phenytoinwith enteral feeding formulas (Nutrison multi fibre sol.). The exact mechanisms underlying this interaction remain unknown and there are severalpossible reasons. Careful monitoring of plasma levels is essential for rational and successful administration of phenytoin, especially, if the patients arechanging tube-feeding regimen or changing from the parenteral to the enteral dosage form of phenytoin.

Key words:
phenytoin – monitoring – enteral feeding – interaction