Clinical Information

Monitoring phenytoin concentrations, along with careful clinical assessment, is the most effective means of improving seizure control, reducing risk of toxicity, and minimizing the need for additional anticonvulsant medication for three reasons. The first being, phenytoin concentrations correlate better with pharmacologic activity than dosage does because of individual differences in absorption, metabolism, disease states, concomitant medication, and compliance. Concentration monitoring helps physicians individualize dosage regimens. Another reason for monitoring is that small changes in dosage can lead to unexpected accumulation and clinical toxicity even within the therapeutic range. This occurs when the hepatic enzyme system for metabolizing phenytoin gets saturated. The final reason for monitoring concentration is that phenytoin is only safe and effective in a narrow range.