Simultaneous quantitation of paracetamol, caffeine, pseudoephedrine, chlorpheniramine and cloperastine in human plasma by liquid chromatography-tandem mass spectrometry.

A rapid and sensitive method based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the simultaneous quantitation of paracetamol, caffeine, pseudoephedrine, chlorpheniramine and cloperastine in human plasma has been developed and validated. After sample preparation by liquid-liquid extraction, the analytes and internal standard (diphenhydramine) were analyzed by reversed-phase HPLC on a Venusil Mp-C(18) column (50mmx4.6mm, 5microm) using formic acid:10mM ammonium acetate:methanol (1:40:60, v/v/v) as mobile phase in a run time of 2.6min. Detection was carried out by electrospray positive ionization mass spectrometry in the multiple-reaction monitoring mode. The method was linear for all analytes over the following concentration (ng/ml) ranges: paracetamol 5.0-2000; caffeine 10-4000; pseudoephedrine 0.25-100; chlorpheniramine 0.05-20; cloperastine 0.10-40. Intra- and inter-day precisions (as relative standard deviation) were all < or =11.3% with accuracy (as relative error) of +/-5.0%. The method was successfully applied to a study of the pharmacokinetics of the five analytes after administration of a combination oral dose to healthy Chinese volunteers.