Abstracts

Rationale: Phenytoin is a well-known antiepileptic drug that is metabolized by zero-order kinetic. Korean food and drug administration(KFDA) approves generic drugs when it shows bioavailability within 80-120% of original drug. As of wide range of bioavailability, generic drugs may show wide range of serum concentration in case of phenytoin. Methods: Phenytoin was inadvertently changed form generic A to generic B from Jun. 2007 to Dec. 2007 in our hospital and total of 174 patients received different generic phenytoin with the same dose. Results: 151 patients were symptom free except mild dizziness in 9 patients.(Group A) Twenty-three patients were admitted via ER or OPD due to severe dizziness or ataxia.(Group B) Age & sex were not different between the groups(M:F=96:55 vs. 18:5, Age=48.8 ± 16.59 vs 50.4 ± 14.12 years) and previous serum concentration was similar (6.04 ± 4.93 µg/ml vs. 7.70 ± 4.29 µg/ml). Follow-up serum concentration was quite different (13.04 ± 7.49 µg/ml vs. 24.91 ± 9.80 µg/ml). The difference between the groups was baseline phenytoin dosage(288.58 ± 66.69mg vs. 344.57 ± 52.74mg). Conclusions: Changing phenytoin from generic to other generic drug may cause severe adverse effects. Only predictor of adverse effect was previous higher dosage of phenytoin.