Carbamazepine toxicity: comparison of measurement of drug levels by HPLC and EMIT and model of carbamazepine kinetics.

A 23-month-old boy accidently ingested 2000 mg (148 mg/kg) of carbamazepine. The delayed onset of convulsions coincided with the peak serum level of total parent drug and an active metabolite (carbamazepine 10,11-epoxide). Comparisons of homogeneous enzyme multiplied immunoassay technique (EMIT) and high pressure liquid chromatography (HPLC) revealed that the EMIT slightly over-estimated plasma carbamazepine levels due to immunochemical cross reactivity with the epoxide metabolite. The peak plasma levels of the parent drug plus the active metabolite were more accurately determined by HPLC. These results emphasize the need to understand both the presence of active metabolites and characteristics of the assay being used in managing clinical intoxication with carbamazepine.