Naproxen (naproxen sodium, NAPROSYN®) is a propionic acid derivative related to the arylacetic acid group of nonsteroidal anti-inflammatory drugs (NSAIDs). It is an anti-inflammatory agent with analgesic and antipyretic properties. Both the acid and its sodium salt are used in the treatment of rheumatoid arthritis and other rheumatic or musculoskeletal disorders, dysmenorrhea, and acute gout. The mechanism of action of the naproxen (naproxen sodium, NAPROSYN®), like that of other NSAIDs, is not completely understood but involves inhibition of cyclooxygenase (COX-1 and COX-2).

6-Methoxy-2-Naphthylacetic acid (6-MNA), an active metabolite of non-steroidal anti-inflammatory drug nabumetone has long half-life and has the tendency to penetrate well into synovial fluid. 6-MNA is a competitive inhibitor of Cox (cyclooxygenases).

(R)-Naproxen is an enantiomer of the more active (S)-Naproxen, the last belongs to the class of Non-Steroidal Anti-Inflammatory Drugs. (S)- and (R)-naproxen represent useful substrates to distinguish different glucuronosyl transferases isozymes.