Sensitive determination of cinnarizine in human plasma by high performance liquid chromatography and fluorescence detection

A sensitive high performance liquid chromatographic method has been developed for the determination of cinnarizine in human plasma. Cinnarizine and clocinizine (internal standard) were extracted from acidified plasma (pH 4.7) into carbon tetrachloride and the organic layer was evaporated. The products were separated on a Microspher C18 (3 μm) column, using a mixture of 0.04 % triethylamine in 0.01 M ammonium dihydrogen phosphate (NH4H2PO4), pH adjusted to 4.2 with orthophosphoric acid (H3PO4), and acetonitrile (20∶80, v/v) as mobile phase, at a flow rate of 1 ml/min at 40°C. Fluorescence detection (λex = 245 nm, λem = 310 nm) was used; the detection limit was 0.5 ng/ml under the conditions used, and the calibration curve linear in the concentration range evaluated (1–60 ng/ml). The assay has been used to measure cinnarizine concentrations in plasma after oral administration to volunteers.