Enzymatic immunoassay vs. gas/liquid chromatography for determination of phenobarbital and diphenylhydantoin in serum.

The antiepileptic drugs diphenylhydantoin and phenobarbital were measured in serum by a new commercially available enzyme immunoassay procedure ("EMIT," Syva Corp.). The procedure requires less than 5 min and no more than 50 mul of serum per determination. It is simple; only four steps (pipetting and diluting with an automatic pipettor-dilutor) are required before spectrophotometry. Twenty replicate analyses of a serum containing phenobarbital and diphenylhydantoin gave results with a CV of 6.8% and 9.1%, respectively. Results attained in a large series of patients were compared with results by a gas/liquid chromatographic procedure. For phenobarbital r = 0.97, and for diphenylhydantoin r = 0.98. No false negatives or false positives were encountered.