Aspirin, also known as acetylsalicylic acid, is a nonsteroidal anti-inflammatory drug NSAID that is commonly used to relieve pain, reduce inflammation, and lower fever. It works by specifically targeting and inhibiting the enzyme cyclooxygenase-2 COX-2 in the prostaglandin biosynthesis pathway.Cyclooxygenase enzymes, including COX-1 and COX-2, are responsible for the conversion of arachidonic acid to prostaglandins, which are lipid compounds that play a crucial role in mediating inflammation, pain, and fever. COX-1 is constitutively expressed in most tissues and is involved in maintaining normal physiological functions, while COX-2 is induced during inflammation and is responsible for the production of prostaglandins that cause pain and inflammation.Aspirin exerts its anti-inflammatory and analgesic effects by irreversibly inhibiting both COX-1 and COX-2 enzymes through the acetylation of a serine residue Ser-530 in COX-1 and Ser-516 in COX-2 in the active site of the enzymes. This acetylation blocks the access of arachidonic acid to the active site, preventing the formation of prostaglandins.Although aspirin inhibits both COX-1 and COX-2, its selectivity for COX-2 is thought to be responsible for its anti-inflammatory and analgesic effects. This is because COX-2 is primarily involved in the production of prostaglandins that mediate inflammation and pain, while COX-1 is more involved in maintaining normal physiological functions. By inhibiting COX-2, aspirin effectively reduces the production of prostaglandins, leading to reduced inflammation and pain relief.It is important to note that aspirin's inhibition of COX-1 can also lead to some of its side effects, such as gastrointestinal irritation and increased bleeding risk, as COX-1 is involved in maintaining the protective lining of the stomach and promoting platelet aggregation.