Acetaminophen-13C2,15N is the 13C and 15N labeled Acetaminophen[1]. Acetaminophen (Paracetamol) is a selective cyclooxygenase-2 (COX-2) inhibitor with an IC50 of 25.8 µM,is a widely used antipyretic and analgesic agent[2][3][4]. Acetaminophen is a potent hepatic N-acetyltransferase 2 (NAT2) inhibitor[5].