Plasma protein binding of diphenylhydantoin in patients with epilepsy; Agreement between the unbound fraction in plasma and the concentration in the cerebrospinal fluid

Abstract

The plasma protein binding and the cerebrospinal fluid (CSF)‐plasma ratio of diphenyhydantoin (DPH) was determined in 8 patients with epilepsy treated only with DPH and in steady‐state conditions. The unbound fraction of DPH showed only minor interindividual differences and did not differ from the values in drug‐free volunteers. The CSF‐plasma ratio also varied very little interindividually and agreed well with the values of the unbound fraction. The discrepancy between our results and those of previous investigators is discussed.