Prostaglandin-endoperoxide synthase (also known as cyclooxygenase) (COX (for the enzyme family), PTGS (for the gene/protein family); specific isoforms are COX-1, COX-2, and sometimes COX-3)

Prostaglandin-endoperoxide synthases (cyclooxygenases, COXs) are key enzymes that catalyze the conversion of arachidonic acid into prostaglandins and thromboxanes via an intermediate step involving formation first of prostaglandin G₂, then reduction to prostaglandin H₂, which serves as a precursor for all other biologically active prostanoids. There are two main functional human isoforms—COX‑1/PTGS1 is constitutively expressed for physiological “housekeeping” roles like gastric protection; while inducible COX‑2/PTGS2 mediates inflammatory responses. These enzymes are primary targets for NSAIDs used widely against pain and inflammation. The term “Prostaglandin G/H synthase 3” refers either to a non-functional splice variant (“COX‐3”) or an obsolete/unrecognized entity in humans—it does not represent a distinct therapeutic target.[1][6]

Other names

CyclooxygenaseCOXProstaglandin G/H synthasePGHSCOX‑1PTGS1PGHS‑1COX‑2PTGS2PGHS‑2

Drugs typically act by reversible or irreversible inhibition of cyclooxygenases, thereby blocking conversion of arachidonic acid to prostaglandins/thromboxanes—reducing inflammation, pain, fever. NSAIDs cause non-selective/reversible inhibition. Aspirin causes irreversible acetylation/inhibition. Coxibs cause selective reversible inhibition of COX‑2.