Selective COX-2 inhibitor

Selective COX-2 inhibitor

The PG that mediates inflammation, fever, and pain are produced solely via COX-2 (highly inducible by inflammatory response), and the PGs that are important in GIT, platelets, uterus, and adrenal function are produced solely via COX-1 (constitutively expressed). Selective COX-2 inhibitors (Celecoxib, Rofecoxib, and Valdecoxib) are devoid of side effects, such as gastric ulcer. It does not affect the normal functioning of platelets, uterus, and renal system.

i. Celecoxib (Celact, Cobix, Revibra)

Metabolism: Metabolism of celecoxib occurs in the liver, involves hydroxylation of 4-methyl group to primary alcohol, which is subsequently oxidized to its corresponding carboxylic acid.

Properties and uses: It exists as pale yellow crystals, sparingly soluble in water. Celecoxib is used to treat arthritis, pain, menstrual cramps, and colonic polyps, and also for the relief of pain, fever, swelling, and tenderness caused by osteoarthritis, rheumatoid arthritis and ankylosing spondylitis.

Synthesis

Dose: For osteoarthritis, the adult dose is 200 mg as a single dose or in two divided doses that may be increased to 200 mg two times a day, if necessary. For rheumatoid arthritis, the adult dose is 100–200 mg two times a day. For elderly people the dose is 100 mg two times a day. For dysmenorrhoea, initially the dose is 400 mg by 200 mg, if necessary, on the 1st day and maintenance dosage is 200 mg two times a day.

ii. Rofecoxib

Synthesis

Metabolism: The metabolic route of Rofecoxib appears to follow the reduction of dihydrofuranone ring system by cystolic enzyme to cis and trans hydroxy derivatives.

Properties and uses: It exists as white to light yellow powder, sparingly soluble in acetone, methanol, very slightly soluble in 1-octanol. It is a COX-2 inhibitor with greater potency and a longer half-life than celecoxib. Rofecoxib is used to relieve the pain, tenderness, inflammation (swelling), and stiffness caused by arthritis, and to treat painful menstrual periods and pain from other causes.

iii. Valdecoxib

Synthesis

Metabolism: It is metabolized by hydroxylation of 5-methyl group and it is further metabolized to inactive carboxylate and N-Hydroxylation at the sulphonamide function, leading to the formation of corresponding sulphinic acid and suphomic metabolites.

Properties and uses: It is soluble in most organic solvents, insoluble in water. It is a NSAID drug that exhibits anti-inflammatory, analgesic, and antipyretic activities.

Dose: For dysmenorrhoea the dose is 20 mg twice a day. For osteoarthritis and rheumatoid arthritis the dose is 10 mg once daily.