Quantitative Determinations of Phenobarbital and Carbamazepine in Serum by Nephelometric Immunoassay

An automated rate nephelometric assay (Beckman Array 360 System) for phenobarbital (PB) and carbamazepine (CBZ) was evaluated. The assay offers measuring ranges of 5-120μg/ml serum for PB and 2-40μg/ml for CBZ. The coefficients of variation for within-run and between-run precision for both PB and CBZ were< 5.0%. Test results were not significantly affected by bilirubin-unconjugated (up to 19.2 mg/ dl), bilirubin-conjugated (21.3 mg/dl), hemoglobin (540 mg/dl), turbidity (2070 units), or other antiepileptic drugs. The method produced satisfactory results in dilution tests. Quantitative results obtained by the Array 360 assay on serum samples from patients were compared with those obtained by the fluorescence polarization immunoassay (FPIA) and homogeneous enzyme immunoassay (EMIT) methods. The results correlated well with FPIA (r=0.996 and 0.981 for PB and CBZ, respectively) and EMIT (r=0.994 and 0.983). The Array 360 assay was concluded to be an appropriate and quick method for PB and CBZ determination.