Liquid Chromatography-Tandem Mass Spectrometry Method for the Quantification of Fentanyl and its Major Metabolite Norfentanyl in Critically Ill Neonates

Abstract

Fentanyl is a widely used opioid analgesic in the intensive care unit. In critically ill neonates, continuously infused fentanyl is part of the standard treatment regimen for sedation and pain control. Little is known about fentanyl pharmacokinetics in specific clinical indications, as in asphyxiated neonates with therapeutic hypothermia treatment. In this report, we introduce a liquid chromatography-tandem mass spectrometry method (LC-MS/MS-method) to determine concentrations of fentanyl and its major metabolite norfentanyl in critically ill newborns. 100 μl serum samples were precipitated with acetonitrile containing the isotopically labeled internal standard fentanyl-D5. The supernatant was evaporated to dryness and reconstituted with mobile phase. Chromatographic separation was achieved on a C18 column with a gradient flow. LC-MS/MS detection was performed using a triple-stage quadrupole mass spectrometer working in selected reaction monitoring mode with positive electrospray ionization. Linearity was demonstrated over the concentration range of 0.1 to 40 and 39.4 ng/ml for fentanyl and norfentanyl respectively. Inter- and intraday accuracies and precisions were within the acceptance ranges. The lower limit of quantification was 0.02 and 0.09 ng/ml for fentanyl and norfentanyl. The method was successfully applied to newborns with hypoxic-ischemic encephalopathy treated with whole body hypothermia, which allowed accurate determination of fentanyl and norfentanyl concentrations as a basis for pharmacokinetic analysis.