Xylazine Exacerbates Fentanyl-Induced Respiratory Depression and Bradycardia

Area of Science:

• Pharmacology and Toxicology
• Respiratory Physiology
• Neuroscience

Background:

• Fatal opioid overdoses have surged, with synthetic opioids like fentanyl implicated in over 92% of cases.
• Illicit fentanyl is increasingly adulterated with xylazine, a veterinary anesthetic, raising overdose concerns.
• Xylazine potentiates fentanyl's lethality, but the underlying mechanisms remain unclear.

Purpose of the Study:

• To investigate the respiratory and cardiovascular effects of fentanyl, xylazine, and their combination.
• To elucidate the mechanisms by which xylazine exacerbates fentanyl-induced respiratory depression and lethality.

Main Methods:

• Whole-body plethysmography was used to measure respiratory rate and patterns in mice.
• Pulse oximetry assessed blood oxygen saturation and heart rate.
• Effects of fentanyl, xylazine, and their combination were evaluated in male and female CD-1 mice.

Main Results:

• Xylazine significantly decreased breathing rate by prolonging expiration, while fentanyl primarily inhibited inspiration.
• The combination of fentanyl and xylazine exacerbated fentanyl-induced respiratory inhibition.
• Fentanyl, but not xylazine, reduced blood oxygen saturation; xylazine did not alter fentanyl-induced hypoxia levels but reduced heart rate.

Conclusions:

• Xylazine worsens fentanyl-induced respiratory depression by exacerbating inspiratory inhibition.
• Reduced blood oxygen saturation correlated with fentanyl-induced apneas, not breathing rate.
• These findings offer mechanistic insights into the increased overdose risk associated with fentanyl-xylazine adulteration.