Polarisation fluoroimmunoassay of phenytoin.

A polarisation fluoroimmunoassay for the determination of phenytoin levels in serum is described. Fluoresceinthiocarbamyl alpha,alpha-diphenylglycine (FTC-DPG) is used as an easily prepared fluorescent-labelled analogue of phenytoin. Interference from the non-specific binding of FTC-DPG by serum proteins is eliminated by proteolytic degradation of samples prior to assay. The method employs stable, non-radioactive reagents, requires no separation procedure, and involves only 1.25 microliter of serum. Analyses of serum samples from patients receiving phenytoin correlate well (r = 0.96) with an established gas-liquid chromatographic method.