INVIVO INTERACTION OF ANTICONVULSANT DRUGS - MATHEMATICAL CORRELATION OF PLASMA-LEVELS OF ANTICONVULSANT DRUGS IN EPILEPTIC PATIENTS

The phenytoin plasma levels were measured in 45 epileptic patients whose only treatment was phenytoin. The plasma of 20 other patients receiving both phenytoin and phenobarbital was also tested for the concentration of these 2 drugs and 18 patients treated with phenytoin, phenobarbital and primidone were investigated in the same way. The plasma levels of phenytoin were calculated in relation to dosage and to measure the effect of the simultaneous use of phenobarbital on the phenytoin plasma levels and of pyrimidone together with phenobarbital on phenytoin concentration. The population of epileptic patients can be divided into 2 groups. In the 1st group the patients reach equilibrium at the relatively high phenytoin plasma level for a given dose of phenytoin, and in the 2nd group the phenytoin plasma level tends to be significantly lower for parallel dosages. Both groups, in their behavior, obey mathematically an exponential graph specific for each group. Phenobarbital tends to lower the plasma phenytoin level when the 2 drugs are used simultaneously. It is also possible, by the graphs produced, to calculate the expected phenytoin plasma levels when using the drugs together. Primidone and phenobarbital together decrease the phenytoin level much more than expected from the effect of phenobarbital alone.