Phenytoin and phenobarbital protein binding alterations in a uremic burn patient

A case is reported in which dramatic decreases in the protein binding of phenytoin and phenobarbital were noted. A 57-year-old burn patient with a history of a seizure disorder had increased free fractions of phenytoin and phenobarbital. The patient later developed renal failure and the free fractions of both drugs were further increased. Decreases in the protein binding of phenytoin in patients with hypoalbuminemia and/or uremia have been well documented, but the effects of these conditions on phenobarbital protein binding have not been well studied. In the case described here, the presence of both hypoalbuminemia and uremia were necessary before a doubling of the free fraction of phenobarbital was noted. Although it is not a highly protein-bound drug, in some circumstances protein binding alterations of phenobarbital may be of clinical significance.