Notes: 4-hydroxy Diclofenac is an active metabolite of the non-steroidal anti-inflammatory drug (NSAID) and COX inhibitor diclofenac (Item Nos. 70680 / 22983).{14145} It is formed from diclofenac by the cytochrome P450 (CYP) isoform CYP2C9 in human liver microsomes.{65583} 4-hydroxy Diclofenac inhibits COX activity (IC50 = 32 nM) and reduces prostaglandin E2 (PGE2; Item No. 14010) production (IC50 = 17 nM) in isolated human rheumatoid synovial cells.{28498}