Evaluation of the Cloned Enzyme Donor Immunoassay for Measurement of Phenytoin and Phenobarbital in Serum

We report the evaluation of the cloned enzyme donor immunoassay (CEDIA) for the estimation of phenytoin and phenobarbital in serum. The assays were performed with a Hitachi 911 analyzer. Intra-assay coefficients of variation were from 1.5 to 4.4% for phenytoin and 1.6 to 5.5% for phenobarbital. Interassay coefficients of variation ranged from 1.8 to 5.3% for phenytoin and 2.9 to 4.8% for phenobarbital. Linearity was satisfactory, with a recovery of 103% at 11 mg/L and 110% at 22 mg/L phenytoin and 93% at 14 mg/L and 101% at 40 mg/L for phenobarbital. The detection limit was 1.2 mg/L for phenytoin and 0.6 mg/L for phenobarbital. Results of this assay correlated well with those of a conventional high-performance liquid chromatography (HPLC) method; r = 0.99 for phenytoin (n = 47) and r = 0.98 for phenobarbital (n = 48). The CEDIA was easy to handle and especially suitable for short turn-around time application.