SIMULTANEOUS DETERMINATION OF DEXTROMETHORPHAN AND DEXTRORPHAN IN HUMAN PLASMA, URINE AND CEREBROSPINAL-FLUID BY HPLC WITH FLUORESCENCE DETECTION

Dextromethorphan is a non-narcotic antitussive drug that recently attr acted interest because of its anticonvulsant and neuroprotective prope rties. Dextromethorphan undergoes polymorphic oxidation and 5-10% of h uman subjects are characterised as poor metabolizers on the basis of t he formation rate of its O-demethylated metabolite, dextrorphan cataly sed by isozyme CYP2D6. A sensitive, selective and reliable high perfor mance liquid chromatographic (HPLC) method for the simultaneous determ ination of dextromethorphan and dextrorphan in human plasma, urine, an d cerebrospinal fluid, is described, using levallorphan as the interna l standard. The analytes were extracted from biological fluids by a li quid-liquid extraction procedure. The chromatographic separation was p erformed on a 5-mu M cyano analytical column (220 x 4.6 mm) using a mi xture of acetonitrile/distilled water/n-octylamine (19/80.95/0.05, v/v ) pH 2.8 as the mobile phase with a flow rate of 1.0 mL/min at 40 degr ees C and the chromatographic peaks were measured by fluorescence dete ction. The calibration curves were linear with a correlation coefficie nt of 0.999 or better from 1-100, 5-500, and 1-100 ng/mL for both drug s in plasma, urine, and cerebrospinal fluid, respectively The method w as not interfered with by other endogenous components or concurrent an tiepileptic drugs. The within-day precision of the method was evaluate d for three concentrations and was found to be less than 6%, and the a ccuracy was nearly 100%.