Clinical significance of serum phenytoin level

Phenytoin serum concentrations in 115 epileptics treated on an inpatient basis showed, in two groups, only relatively weak correlation with the dosage used. The range of variation was assigned a factor of 16. For individual patients there was observed a correlation between the dosage in mg/kg and the corresponding phenytoin serum concentration. The level of phenytoin serum concentration was not found to be related to the frequency of attacks. The effective phenytoin serum level showed interindividual differences and can be low as well as relatively high. Resulting from this is the need for determining, from the determination of serum concentrations, the effective serum concentration for each individual patient.