Liquid chromatography tandem mass spectrometry for the simultaneous quantitative analysis of ketamine and medetomidine in ovine plasma

Ketamine and medetomidine are commonly combined to sedate or anaesthetize a wide range of animal species. Despite this, there are few methods for the simultaneous quantitative analysis of the two drugs. This study describes the use of solid‐phase extraction sample preparation followed by liquid chromatography–tandem mass spectrometry for the quantitative analysis of both drugs in ovine plasma. Extraction recovery was 93% for ketamine and 95% for medetomidine. The lowest limit of detection for ketamine was 1 ng/mL and for medetomidine 2 ng/mL, with linearity greater than 0.99 for both. Intra‐day and inter‐day precisions for both drugs were less than 10 and 7%, respectively. Application of the method to samples obtained from pregnant ewes and their fetuses showed placental transfer of the drugs over time such that there was no significant difference in plasma concentration at delivery. In summary, a validated method has been developed for the simultaneous quantification of ketamine and medetomidine in ovine plasma samples which can be used to study the pharmacokinetics of these drugs. Copyright © 2011 John Wiley & Sons, Ltd.