Researchers have 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 study findings were published in Forensic Toxicology.

Illicit psychoactive substances (e.g., synthetic cannabinoids, cathinone derivatives, and synthetic opioids) have become a serious threat worldwide as designer drugs of abuse. Mepirapim is a new and unique synthetic cannabinoid that was first identified in herbal blends in Japan. Acetyl fentanyl is a synthetic fentanyl analogue in which the propionyl group of fentanyl is replaced by an acetyl group.

In forensic toxicology, investigation of the concentrations in biological fluid samples is critical for estimating the cause of death and the time elapsed after dosing. In this study, the investigators encountered a curious case in which two male subjects self-administered mepirapim plus acetyl fentanyl by different routes, i.e., intravenously and by inhalation.

Thus, the investigators have 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.

The concentrations of acetyl fentanyl in heart whole blood, femoral vein whole blood, and urine of the deceased individual with administration by intravenous injection 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.

In conclusion, the investigators said to their 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 the laboratory.