Norcarfentanil: carfentanil misuse or remifentanil treatment?

Purpose Since the early 2010s, deaths due to the use of new synthetic opioids (NSO) including fentanyl and its analogs have been increasing dramatically. As fentanyl analogs bear strong structural similarities, they can share common metabolites. In some clinical or forensic cases, it can be important to demonstrate the presence of both the metabolite and the parent product to confirm that the compound is responsible for the intoxication. Norcarfentanil is a common metabolite of carfentanil (NSO) and remifentanil (widely used in medical care). This article reported the investigation of norcarfentanil origin in three cases. Methods Comprehensive screenings were performed using gas chromatography coupled to mass spectrometry and liquid chromatography coupled to a diode array detection, whereas targeted screening of NSO were performed using liquid chromatography coupled to tandem mass spectrometry. Results Norcarfentanil was detected at concentrations ranging from 0.05 to 15.8 ng/mL in plasma and from 8.8 to 1820 ng/mL in urine, but carfentanil was detected in two out of the three cases. The presence of norcarfentanil has been supposed to be due to the treatment with remifentanil during the medical care of the patient. Conclusions In the first two cases, norcarfentanil was present as the metabolite of carfentanil, whereas in the last case, norcarfentanil was the metabolite of remifentanil. Without the identification of remifentanil, confusion could occur, and norcarfentanil could be attributed to carfentanil misuse.