Analgesics, Antipyretics, and NSAIDs

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Chapter: Medicinal Chemistry : Analgesics, Antipyretics, and NSAIDs

Nonsteroidal anti-inflammatory drugs (NSAIDs) are used primarily to treat inflammation, mild-to-moderate pain, and fever.


Analgesics, Antipyretics, and NSAIDs

 

INTRODUCTION

Nonsteroidal anti-inflammatory drugs (NSAIDs) are used primarily to treat inflammation, mild-to-moderate pain, and fever. Specific uses include the treatment of headache, arthritis, sports injuries, and menstrual cramps. Aspirin is used to inhibit the clotting of blood and prevent strokes and heart attacks in individuals at high risk. NSAIDs are also included in many cold and allergic preparations.

NSAIDs are associated with a number of side effects. The frequency of side effects varies according to the drugs; the most common side effects are gastro intestinal tract (GIT) disturbances, such as nausea, diarrhoea, constipation, vomiting, decreased appetite, and peptic ulcer. NSAIDs may also cause fluid retention, leading to oedema; the most serious side effects are kidney failure, liver failure, ulcers, and prolonged bleeding after an injury of surgery. Some individuals are allergic to NSAIDs and may develop shortness of breath when NSAIDs are administered. People with asthma are at a higher risk for experiencing serious allergic reaction to NSAIDs. Use of aspirin in children and teenagers with chicken pox or influenza has been associated with the development of Reye’s syndrome. Therefore, aspirin and salicylate should not be used in children and teenagers with suspected or confirmed chicken pox or influenza.

Antipyretics are the drugs that reduce the elevated body temperature. Anti-inflammatory agents are used to cure or prevent inflammation caused by prostaglandin (PGE2). These drugs are widely utilized for the alleviation of minor aches, pains, fever, and symptomatic treatment of rheumatic fever, rheumatoid arthritis, and osteoarthritis. The biosynthetic pathway of prostaglandins (PGs) is depicted in Figure 3.1


 

General Structure of PG

PG is a naturally occurring 20-carbon cyclopentano fatty acid derivative, derived from arachidonic acid.


Mode of action: NSAIDs inhibit cycloxygenase (COX), the enzyme that catalyses the synthesis of cyclic endoperoxides, from the arachidonic acid to form PGs. The two COX isoenzymes are COX-1 and COX-2. The function of COX-1 is to produce PGs that are involved in normal cellular activity, (protection of gastric mucosa, maintenance of kidney function). While, COX-2 is responsible for the production of PGs at the inflammation sites. Most NSAIDs inhibit both COX-1 and COX-2 with varying degree of selectivity. Selective COX-2 inhibitor may eliminate the side effects associated with NSAIDs due to COX-1 inhibition, such as gastric and renal effect.

 

SIDE EFFECTS

In stomach: Biosynthesis of PGs, especially PGE2 and PGI2, serves as cytoprotective agents in gastric mucosa; these PGs inhibit acid secretion by the stomach, enhance mucosal blood flow, and promote the secretion of cytoprotective mucus in the GIT. Inhibition of the PGs synthesis may make the stomach more susceptible to damage and lead to gastric ulcer.

In platelets: Platelet’s function get disturbed because NSAIDs prevent the formation of Thromboxane A2 (TXA2) in platelets, as TXA2 is a potent platelet-aggregating agent. This accounts for the tendency of these drugs to increase the bleeding time and this side effect has been exploited in the prophylactic treatment of thromboembolic disorder.

In uterus: NSAIDs prolong gestation because of the inhibition of PGF2 in uterus. PGF2 is a potent uterotropic agent and their biosynthesis by uterus increase dramatically in the hours before parturition. Accordingly, some anti-inflammatory drugs have been used as a colytic agent to inhibit preterm labour.

In kidney: NSAIDs decrease renal blood flow and the rate of glomerular filtration in patients with congestive heart failure, hepatic cirrhosis, and with chronic renal disease, in addition, they prolong the retention of salt and water, this may cause oedema in some patients.

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