Cloud-point extraction for the determination of the free fraction of antiepileptic drugs in blood plasma and saliva.

A method for the determination of the free fraction of antiepileptic drugs in plasma and saliva was developed. The separation of free and protein-bound fractions was obtained by cloud-point extraction under optimum conditions of pH, surfactant type, and concentration. It is shown that the free fraction of carbamazepine and of phenobarbital in plasma coincides with the drug concentration in saliva. The dependence of the free fraction in plasma on the administered dose was studied. The influence of the simultaneous administration of the two drugs on their free concentrations was revealed: In the presence of carbamazepine the free fraction of phenobarbital is decreased markedly whereas phenobarbital does not influence the behavior of carbamazepine.