Measurement of ketamine and xylazine in rat brain by liquid-liquid extraction and gas chromatography-mass spectrometry

J Pharmacol Toxicol Methods. 2016 Jan-Feb:77:6-9. doi: 10.1016/j.vascn.2015.09.001. Epub 2015 Sep 9.

Abstract

Introduction: In human and veterinary medicine, the injectable drugs ketamine and xylazine are mainly used in combination to induce, and then maintain general anaesthesia; they also provide pain and stress relief. Some side-effects have been reported on the auditory brainstem response, a method is therefore required to determine their concentrations in the brain.

Methods: This paper presents a method to determine nanogramme quantities of ketamine and xylazine in rat brain using liquid-liquid extraction and gas chromatography-mass spectrometry in selective ion monitoring mode. The technique requires only 0.5 g of sample, and uses xylazine d6 as an internal standard.

Results: The method was linear between 0.86 and 34.4 μg/g of brain. Limits of quantification were 378 and 87 ng (approximately 0.76 and 0.17 μg/g of brain) for ketamine and xylazine, respectively. The reliability of the method in terms of accuracy, within-day and between-day precision was also demonstrated. For xylazine, bias and intra-day precision were good (<3.0%), as was between-day precision (<10.5%); the equivalent values for ketamine were 7%, 11.1% and 20.9%, respectively. Stability of the analytes in the matrix at -80 °C was assessed over five months; both compounds were found to be stable for at least 1 month, even at very low concentrations. The procedure was successfully applied to determine (for the first time) the in vivo brain levels of both drugs in animals following systemic administration.

Discussion: The procedure will be useful in future studies of the side-effects of these drugs, and their interactions with other compounds.

Keywords: Brain; GC/MS; Ketamine; Xylazine.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Brain / metabolism*
  • Gas Chromatography-Mass Spectrometry / methods
  • Ketamine / metabolism*
  • Liquid-Liquid Extraction / methods
  • Male
  • Rats
  • Xylazine / metabolism*

Substances

  • Xylazine
  • Ketamine