Brain concentrations of phenytoin, phenobarbitone and primidone in epileptic patients.

Plasma, brain, lumbar CSF, skeletal muscle, skin and bone concentrations of phenytoin, phenobarbitone and primidone have been measured in specimens from patients undergoing temporal lobectomy for chronic epilepsy. A good correlation was found between the plasma and brain concentrations of each drug. Similarly, a good correlation was found between the plasma and CSF concentrations of each drug. Assuming that CSF is an ultrafiltrate of plasma, the percentage of phenytoin, phenobarbitone and primidone which was unbound in plasma was 10-14%, 43% and 81% respectively. Skeletal muscle concentrations of phenytoin and phenobarbitone and the skin concentration of phenytoin, also correlated with the plasma concentrations, but the remaining tissues did not give significant correlations.