Identification and quantification of mepirapim and acetyl fentanyl in authentic human whole blood and urine samples by GC-MS/MS and LC-MS/MS

We encountered a curious case in which two male subjects self-administered mepirapim plus acetyl fentanyl by different routes, i.e., intravenously and by inhalation. We have thus established a detailed procedure for quantification of mepirapim and acetyl fentanyl in whole blood and urine specimens using gas chromatography (GC)-tandem mass spectrometry (MS/MS).

The GC-MS/MS method was validated for linearity, extraction recovery, accuracy, and precision. Liquid chromatography-MS/MS was also used for identification of the target compounds.

Good linearity and reproducibility were achieved in the range of 20-1000 ng/g for both target compounds in both matrices. The concentrations of mepirapim in heart whole blood, femoral vein whole blood, and urine of the deceased individual with administration by intravenous injection were 593, 567, and 527 ng/g, respectively; those of acetyl fentanyl were 155, 125, and 126 ng/g, respectively. The mepirapim and acetyl fentanyl concentrations in the urine specimen of the surviving individual who had administered them by inhalation were 4900 and 570 ng/g, respectively.

To our knowledge, with the exception of a brief mention of a mepirapim concentration in a serum sample in emergency medicine, there are no reported data on the identification and quantification of mepirapim in biological samples. Mepirapim is a new synthetic cannabinoid. The concentration profiles of unchanged mepirapim in whole blood and urine were quite different and unique. A detailed clarification of such uniqueness is under way in our laboratory.