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).

Naproxen etemesil is a lipophilic, non-acidic, inactive prodrug of the non-steroidal anti-inflammatory drug (NSAID) naproxen that is hydrolysed to pharmacologically active naproxen once absorbed. Naproxen etemesil was in development with Logical Therapeutics for the treatment of osteoarthritis. However, no recent development has been reported. It is also in phase I clinical trials for the treatment of inflammation and arthritis.The compound was originally developed by Medinox, licensed to Logical Therapeutics in 2006 for partial rights.

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.

Naproxen methyl ester, a mixture of two isomers R and S, is the precursor of therapeutically important nonsteroidal anti-inflammatory drug naproxen. Naproxen methyl ester can be enantioselectively hydrolyzed by lipases or (S)-enantioselective esterase could catalyze the selective hydrolysis of the (S)-Naproxen methyl ester, giving optically pure (S)-naproxen. In addition, S-naproxen methyl ester is used as a tool for identification and determination of new stereo selective carboxylesterase activities.