Tolfenamic acid-d4 is the deuterium labeled Tolfenamic Acid. Tolfenamic Acid (GEA 6414) is a non-steroidal anti-inflammatory and anti-cancer agent, selectively inhibits COX-2, with an IC50 of 13.49 μM (3.53 μg/mL) in LPS-treated (COX-2) canine DH82 monocyte/macrophage cells, but shows no effect on COX-1[1][2].