“…The disposition of tramadol in the human body and its eventual association with clinical and toxicological aspects were typically obtained by plasma and urine testing (Nobilis et al, 1996;Levine et al, 1997;Yeh et al, 1999). However, in the last two decades, the quantification of tramadol in other matrices has gained increasing importance, including in oral fluid (Wylie et al, 2005;Moore et al, 2007;El-Sayed et al, 2011), liver, bile, kidney, gastric content, vitreous humor, lung, heart, brain, spleen and muscle (Bogusz et al, 1998;Musshoff and Madea, 2001;Clarot et al, 2003;Oertel et al, 2011). In the case of M1, the quantification studies are scarce compared with conventional samples (blood, plasma and urine).…”