Phenytoin dosing in obese patients: two case reports

Phenytoin is used extensively in the treatment of various forms of epilepsy, and remains the drug of choice in partial and generalized tonic-clonic seizures. Because it demonstrates saturable, Michaelis-Menten pharmacokinetics, dosing of phenytoin within the therapeutic range can be very challenging, especially so in obese patients. We present case reports of two obese patients each requiring very large doses of phenytoin sodium (1000 mg/d) to sustain therapeutic serum concentrations and seizure control. There are very few reports in the literature regarding phenytoin pharmacokinetic changes in the obese. We can only theorize possible changes in these parameters. Further investigation in the form of controlled research trials need to be performed before final dosage recommendations can be given.