Flunixin is a non-steroidal anti-inflammatory drug (NSAID) used in veterinary medicine to treat pain and inflammation in horses and other animals. Flunixin stable isotopes are labeled forms of the drug that contain atoms with different numbers of neutrons. These isotopes are used in biological and pharmacological research to track the absorption, distribution, metabolism, and excretion of the drug in living organisms. The stable isotopes of flunixin can also be used to develop more sensitive and accurate analytical methods for measuring drug levels in biological fluids and tissues.