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. 
Naphazoline (in the hydrochloride form) is the common name for 2-(1-naphthylmethyl)-2-imidazoline hydrochloride. It is a sympathomimetic agent with marked alpha adrenergic activity. It is a vasoconstrictor with a rapid action in reducing swelling when applied to mucous membrane . It acts on alpha-receptors in the arterioles of the conjunctiva to produce constriction, resulting in decreased congestion. It is an active ingredient in several over-the-counter formulations including Clear Eyes and Naphcon eye drops .