Acetaminophen- 13 C 2 , 15 N is the 13 C and 15 N labeled Acetaminophen. 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. Acetaminophen is a potent hepatic N-acetyltransferase 2 (NAT2) inhibitor.