Establishment to measure oxycodone in plasma with liquid chromatography–tandem mass spectrometry

Oxycodone (OXY) is classified as a “strong opioid” in the World Health Organization system of cancer pain treatment. However, OXY also causes severe adverse reactions, such as respiratory depression. Thus, in order to adjust the dosage of OXY for well‐managed pain relief with less toxicity, we tried establishing and validating a system for measuring plasma concentrations of OXY using liquid chromatography–tandem mass spectrometry (LC–MS/MS). Human pooled plasma samples containing OXY diluted with 0.1% formic acid solution and internal standard (papaverine) were used for solid‐phase extraction. The eluents were injected into LC–MS/MS with Unison UK‐Silica column (100 × 2 mm, 3 μm, Imtakt). Mobile phase was a mixture of 1 mM ammonium formate solution and acetonitrile containing 0.1% formic acid (50:50). OXY in plasma could be measurable with good linearity in a concentration range of 2–100 ng/ml by using 100 μl of plasma within 4 min. Relative standard deviations of all validation results were within ±15%. These results suggest that our established method using LC–MS/MS to measure OXY in plasma would be useful to adjust the dosage of OXY in order to obtain its efficacy and to avoid its adverse reactions.