Simultaneous determination of zonisamide, carbamazepine and carbamazepine-10,11-epoxide in infant serum by high-performance liquid chromatography

This study developed a simple method for the simultaneous determination of zonisamide (ZNS), carbamazepine (CBZ) and its active metabolite, carbamazepine-10,11-epoxide (CBZE) in infant serum using reversed-phase high-performance liquid chromatograph (HPLC). The method involves a single-step protein precipitation procedure that uses no solid-phase or liquid–liquid extraction. The HPLC separation was carried out on a Cadenza CD-C18 column (3 μm, 4.6 mm × 150 mm) with potassium phosphate buffer (pH 4.6; 25 mM)–methanol–acetonitrile (65:20:15 (v/v/v)) as a mobile phase at a 1.0 ml/min flow rate: ZNS was detectable using a UV detector at 235 nm, and both CBZ and CBZE were at 215 nm. The quantification limits were established in accordance with each therapeutic range at 2.5 μg/ml for ZNS, 0.5 μg/ml for CBZ, and 0.25 μg/ml for CBZE. The respective coefficients of variation were 1.3–6.0% and 2.2–7.7% for the intra- and inter-assay.