Determination of ketotifen and its conjugated metabolite in human plasma by liquid chromatography/tandem mass spectrometry: application to a pharmacokinetic study

A sensitive and specific liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed for the investigation of the pharmacokinetics of ketotifen and its major metabolite, ketotifen N ‐glucuronide, in human plasma. The plasma samples were treated by liquid–liquid extraction and analyzed using LC/MS/MS with an electrospray ionization interface. Diphenhydramine was used as the internal standard. The method had a lower limit of quantitation of 10 pg/mL for ketotifen, which offered increased sensitivity, selectivity and speed of analysis, compared with existing methods. The intra‐ and inter‐day precision were measured to be below 8.2% and accuracy between −2.4% and 3.4% for all QC samples. Incubation of the plasma samples with β ‐glucuronidase allowed the quantitation of ketotifen N ‐glucuronide. This quantitation method was successfully applied to a pharmacokinetic study of ketotifen and its major metabolite after oral administration of 2 mg ketotifen fumarate to 16 healthy volunteers. Copyright © 2003 John Wiley & Sons, Ltd.