[Determination of plasma phenytoine and treatment of epileptics]

In the diagnosis of epilepsy the prior approach will be to decide whether it is an epileptic attack or not. If so, is the epilepsy the primary disease or the symptom of an evolving cerebral affection or of a toxic or metabolic disorder? The causes of failure with phenytoin treatment are discussed. They may be exogenous, i.e. prescribing too low a dosage (the average dose in the adult is 5 mg/kg/day) or lack of cooperation by the patient who either takes the drug irregularly or fails to take it at all. The endogenous causes are harder to determine. Plasma phenytoin determination (therapeutic values from [5] to 10 to 20 mug/ml) makes it possible to adapt the dosage to the individual metabolism and sometimes to detect a drug interaction which lowers, and in rarer cases raises, plasma DPH levels. Toxic levels are rarely asymptomatic. In this condition repeated determinations may help to decide when the treatment is to be resumed and thus to avoid recurrence of attacks during or shortly after DPH withdrawal. Finally, plasma determination makes clear the extreme difficulty of adapting the dosage in the rare patients who react to a minimal of dose by a shift in blood level from insufficient to toxic values, or vice versa.