Monitoring of zonisamide in human breast milk and maternal plasma by solid-phase extraction HPLC method

An HPLC method was developed for the determination of zonisamide in human breast milk and plasma. Chromatographic separation was achieved using a Develosil CN analytical column with potassium dihydrogenphosphate buffer (pH 3.5 with milk, pH 2.5 with plasma)-acetonitrile as the mobile phase. Zonisamide and 1, 2-benzisoxazole-3-methansulfonamine acetate as internal standard were detected by ultraviolet absorbance at 240 nm. Zonisamide in breast milk and plasma was extracted by a rapid and simple procedure based on C(18) bonded-phase extraction. Determination of zonisamide in human breast milk and plasma was possible in the concentration range 0.05-20.0 microg/mL. The recoveries of zonisamide added to human breast milk and plasma were 79.5-85.0% and 86.3-93.1%, respectively, with coefficients of variation of less than 8.3% and 11.4% respectively. The mean concentrations of zonisamide in breast milk and plasma were 9.41 +/- 0.95 and 10.13 +/- 0.45 microg/mL, respectively. The average ratio between the breast milk concentration and plasma concentration (M/P ratio) was 0.93 +/- 0.09.