GENERIC drugs produced by different pharmaceutical companies may have different rates of extent of absorption.1-8 This is particularly important to epileptic patients, because most of the antiepileptic medications have low therapeutic indexes. If a patient switches from an antiepileptic preparation with fairly complete absorption to one with less complete absorption, then the serum drug concentration may drop and the patient could have an increased frequency of seizures. If a patient is switched in the other direction, from a less well-absorbed preparation to one that is better absorbed, then the serum concentrations may rise and the patient could have symptoms of toxic effects. Even if the new product has the same completeness of absorption, there may still be a faster or slower rate of absorption that could affect dosing schedules.
These problems have occurred for patients with epilepsy. Previous reports have shown differences in bioequivalence for preparations of phenytoin sodium
Wyllie E, Pippenger CE, Rothner AD. Increased Seizure Frequency With Generic Primidone. JAMA. 1987;258(9):1216–1217. doi:10.1001/jama.1987.03400090100043
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