Effect of sodium valproate on plasma protein binding of diphenylhydantoin

In vivo and in vitro experimental data are presented in support of the hypothesis that sodium valproate displaces diphenylhydantoin (DPH) from plasma protein binding sites. This interaction could have important practical implications in the management of patients on combined therapy with these two drugs. Acute neurological features of DPH intoxication may be precipitated as a result of an increased free (pharmacologically active) fraction, which would not be detected by routine plasma DPH estimations since these reflects largely the bound fraction.