Competitive nephelometric immunoassay method for antiepileptic drugs in patient blood.

We established a competitive nephelometric immunoassay method for the determination of the widely used antiepileptic drugs, phenobarbital and diphenylhydantoin, in human blood plasma. The anti-drug antiserum was collected from the immunized rabbit. The human serum albumin possessing numerous drug moieties was easily prepared for the assay reagent. A laser nephelometer was used to measure the scattered light from the immunoprecipitate. The assay was rapid (incubation time 10 min), required as little as 6 microliters of plasma, required neither troublesome pretreatment nor separation procedure. The patients' plasma specimens were analyzed, and the values correlated well to those determined by the high-performance liquid chromatography (correlation coefficient: 0.983 for phenobarbital, 0.987 for diphenylhydantoin).