Xylazine is metabolized by liver cytochrome P450 enzymes.  When it reaches the liver, xylazine is metabolized and proceeds to the kidneys to be excreted as urine.  Around 70% of a dose is excreted by urine.  Thus, urine can be used in detecting xylazine administration because it contains many metabolites , which are the main targets and products in urine.   Within a few hours, xylazine decreases to undetectable levels.  Other factors can also significantly impact the pharmacokinetics of xylazine, including sex, nutrition, environmental conditions, and prior diseases.