Evaluation of the relationship of xylazine and fentanyl blood concentrations among fentanyl-associated fatalities.

INTRODUCTION: Illicit fentanyl and fentanyl-analogs have produced a devastating increase in opioid fatalities in the United States. Increasingly, xylazine has been found in the illicit fentanyl supply. The role of xylazine in fentanyl intoxication remains unclear. We reviewed coroner records to evaluate trends and effects associated with xylazine in fentanyl-related fatalities.

METHODS: This is a retrospective cohort study of all deaths reported to the Franklin County Coroner's Office in Ohio from 1 January 2019 to 16 March 2023, in which fentanyl was determined causative or contributory to death. Cases identified as fentanyl-associated fatalities were separated into two groups based on whether or not xylazine was also detected.

RESULTS: There were 3,052 fentanyl-related fatalities during the study period. 4.8 percent of these decedents also tested positive for xylazine. There was no meaningful demographic difference between fentanyl-related fatalities in which xylazine was detected versus those without xylazine detected. There was a mean of 726 fentanyl-associated fatalities per year, with a peak of 846 deaths in 2020 and a decline thereafter. The percentage of fentanyl-related fatalities with xylazine detected increased in linear fashion from 2.7 percent in 2019 to 6.6 percent in 2022. The median fentanyl concentration was 17.0 µg/L (inter-quartile range: 7.9, 27.0) in cases with xylazine detected and 10.0 µg/L (inter-quartile range: 5.6, 18.0) without xylazine. The odds of a fentanyl concentration greater than 40 µg/L in cases with xylazine detected was more than twice as great (odds ratio: 2.41; 95% confidence interval: 1.58-3.64) than that in cases without xylazine detected.

CONCLUSIONS: Postmortem fentanyl concentrations were greater in cases with xylazine detected than those without xylazine detected. Though it is unclear why patients who were exposed to xylazine tolerated higher opioid doses prior to succumbing to death, we postulate that xylazine may act to competitively antagonize some degree of mu-opioid receptor binding by opioids.