Acetaminophen is a Cox-1, Cox-2, and Cox-3 (cyclooxygenase) inhibitor. Acetaminophen may be selective for Cox-3 (IC50 values are > 1000, > 1000, and 460 μM for murine Cox-1, murine Cox-2, and canine Cox-3, respectively). Acetaminophen is a widely used analgesic and antipyretic agent.