Fentanyl: cause of death or incidental finding? Postmortem peripheral blood concentrations with and without documented transdermal patch use

Abstract

We reviewed postmortem fentanyl cases to compare peripheral blood (PB) concentrations between deaths caused by fentanyl and deaths in which fentanyl was incidental. Furthermore, we describe PB concentrations in fentanyl-caused deaths with and without transdermal (TD) fentanyl use. Our review produced 20 cases with PB fentanyl. Of these, 13 were determined to be fentanyl-caused deaths. Eight of the 13 involved TD fentanyl. The remaining 7 cases were decedents undergoing therapy with fentanyl (TD, n = 3; intravenous, n = 4). In the 13 fentanyl-caused deaths, the mean PB fentanyl level was 30.1 ng/ml. In the deaths involving TD fentanyl use, the mean fentanyl level was 41.7 ng/ml. Deaths without TD fentanyl use had a mean fentanyl level of 21.3 ng/ml. There were 7 other cases with incidental fentanyl. In 3 of these, therapeutic TD fentanyl was used and the mean PB concentration was 16.6 ng/ml. In the remaining 4 deaths in which therapeutic intravenous fentanyl was employed, the mean PB fentanyl level was 8.1 ng/ml. Our review suggests that a PB fentanyl concentration equal to or greater than 25 ng/ml indicates that fentanyl should be considered as being contributory to or the cause of death. However, ranges of measured PB concentrations are once again shown to overlap between subjects who overdose and those who use fentanyl as prescribed. In addition, fentanyl-caused deaths involving TD fentanyl exposure have higher PB fentanyl concentrations than those who did not use transdermal patches. Although enlightening, our study suggests that further evaluation of fentanyl concentration variability among different postmortem blood specimens is needed.