Additional studies on nicotine exposure in horses: Accurate quantification and elimination profiles of potential biomarkers in plasma and urine.

N'-Hydroxymethylnorcotinine and trans-3'-hydroxycotinine were detected longest in plasma and urine samples after both nicotine and tobacco leaf administrations, and N'-hydroxymethylnorcotinine was deemed most appropriate as a monitoring target due to its relatively higher abundance and slower elimination rate. These two biomarkers could also be used to differentiate sample contamination by tobacco products and genuine nicotine exposure to horse regardless of intentionality.