Vol-7 (1) 2006 BSM.Pmd
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J MEDICINE 2006; 7 : 20-31 REVIEW ARTICLES NON STEROIDAL ANTI INFLAMMATORY DRUGS- AN OVERVIEW M MATIUR RAHMAN1, MD. BILLAL ALAM2, LT. COL. MD. AZIZUL ISLAM3, AKM AMINUL HAQUE4 Epidemiology from the cell membrane phospholipids by a cascade of More than 20 million Americans use various different enzymes. The sequence starts with release of nonsteroidal anti-inflammatory drugs (NSAIDs) on a arachidonic acid from the cell membrane by regular basis, making this class of drugs one of the Phospholipase-A2. Arachidonic acid is then converted most commonly used. Approximately 1 to 2 percent by cyclo oxygenase to prostaglandins, prostacyclin, and of patients taking NSAIDS will develop serious thromboxanes 8. The Cox-1 gene was cloned and gastrointestinal toxicity, which has resulted in 100,000 sequenced in 1988 and in 1991, a second cyclooxygenase to 400,000 hospitalizations per year in the United gene was identified. Celecoxib, the first Cox-2 selective States at a cost of over 2 billion dollars 1-3. In the NSAID got the US FDA approval in 19988-9. United States, 10 to 20,000 peoples died every year of NSAID complications. There are at least 2600 excess Mechanism of action deaths in the United States each year related to Cyclooxygenase inhibition – The primary effect of NSAIDs gastrointestinal toxic reactions in patients with is to inhibit cyclooxygenase (prostaglandin synthase), Rheumatoid Arthritis (RA) who are treated with thereby impairing the ultimate transformation of NSAIDs 4-5. A variety of NSAIDs are readily available arachidonic acid to prostaglandins, prostacyclin, and (at least 20 in the United States and more elsewhere) thromboxanes. The extent of enzyme inhibition varies 6-7 and widely used throughout the world . Although, among the different NSAIDS, although there are no steroid and some other drugs (e.g. Tramadol) have studies relating the degree of cyclooxygenase inhibition value in reducing pain of RA, the content of this article with antiinflammatory efficacy in individual will be limited to NSAIDs only. patients 10. History Two related isoforms of the cyclooxygenase (COX) The first effective analgesic documented in history was enzyme have been described: COX-1 (PGHS-1); and the powder of dried myrtle leaves used in Egypt in COX-2 (PGHS-2). The most important differences 1500 BC. Hippocrates recommended the use of the juice between the two isoforms are the regulation and of the willow and poplar bark for this purpose. In 1763, expression of the enzymes in various tissues: Edward Stone established the efficacy of willow bark • COX-1 is expressed in most tissues, but variably. extract in relieving pain with the help of a clinical trial. It is described as a “housekeeping” enzyme, Salicylic acid was first synthesized in 1860 and it was regulating normal cellular processes (such as shown that all these myrtle leaves, willow and poplar gastric cytoprotection, vascular homeostasis, barks contained salicylic acid. Aspirin, the magic drug platelet aggregation, and kidney function), and of this age, was first synthesized in 1899. Several is stimulated by hormones or growth factors. reports published almost simultaneously in 1971 established that aspirin acted by reducing the • COX-2 is usually undetectable in most tissues; concentration of prostaglandins. More than 25 years its expression is increased during states of ago, Sir John Vane showed that NSAIDs inhibited the inflammation, or experimentally in response to biosynthesis of prostaglandins - mediators of mitogenic stimuli. COX-2 is constitutively inflammation, by inhibiting the key enzyme, expressed in the brain, kidney, bone, and probably prostaglandin endo peroxide synthase or in the female reproductive system. Another cyclooxygenase (Cox) and proposed this as their distinguishing characteristic of COX-2 is that its mechanism of action. He proposed that the same expression is inhibited by glucocorticoids. This mechanism was responsible for the various beneficial observation may contribute to the significant anti- and toxic effects of NSAIDs. Prostaglandins are derived inflammatory effects of the glucocorticoids. 1. Assistant Professor, Department of Medicine, Sir Salimullah Medical College, Dhaka. 2. Associate Professor, Department of Medicine, Dhaka Medical College, Dhaka. 3. Medicine Specialist, CMH, Bogra Cantonment, Bogra. 4. Associate Professor, Department of Medicine, Mymensingh Medical College, Mymensingh. JM Vol. 7, No. 1 Non Steroidal Anti Inflammatory-An Overview Thus, differences in the effectiveness with which a percent of patients who take both over-the- particular NSAID inhibits an isoform of counter (OTC) and prescription NSAIDs. cyclooxygenase may affect both its activity and • Nausea and vomiting – These symptoms may or toxicity. It has been proposed that the perfect NSAID may not be directly related to a local mucosal would inhibit the inducible COX-2 isoform (thereby irritation. The exact incidence with which they decreasing inflammation) without having any effect occur is unknown. on the constitutive COX-l isoform (thereby minimizing toxicity). Three selective COX-2 • Esophagitis – Esophagitis is a relatively common inhibitors, celecoxib, rofecoxib, and valdecoxib have problem that can lead to stricture formation. received approval from the Food and Drug • Peptic ulcers – Gastric ulcers are far more Administration (FDA). These drugs have at least 200 common than duodenal ulcers in patients treated to 300 fold selectivity for inhibition of COX-2 over with NSAIDs. The point prevalence rate for COX-1. COX-2 inhibitors have not been approved for gastric ulcers among NSAID users as use in children 10-13. determined by endoscopic trials is 15 to 30 percent, 10 times that for duodenal ulcers. Both Classification of NSAIDs types of ulcer are usually asymptomatic, and 1. Drug with analgesic and weak anti inflammatory many do not become clinically significant. effect – Aniline derivative. Paracetamol. • Gastrointestinal hemorrhage – The incidence of 2. Drugs with analgesic and mild to moderate anti- NSAID-induced gastrointestinal hemorrhage is inflammatory effect. difficult to define. The published NSAID-induced a. Propionic acid derivatives : Ibuprofen, gastrointestinal complication rate varies from Fenbufen, Fenoprofen, Ketoprofen, 0.1 to 4 percent per year 14; many of these Neproxen patients are bleeding because of NSAID use. b. Fenamic acid derivative : Mefenamic acid. • Gastrointestinal perforation – Perforation is the 3. Drugs with analgesic and marked anti- rarest of the NSAID-induced gastrointestinal inflammatory effect complications; the exact incidence is unknown. a. Salicylic acid derivatives : Aspirin, Salsalate, Mechanism of gastrodeudenal toxicity – An Sodium salicyclate understanding of the mechanism by which NSAIDs b. Pyrazolone derivatives : Azapropazone, induce gastrointestinal mucosal damage requires an Phenyl butazone understanding of normal gastric anatomy and c. Acetic acid derivatives : Diclofenac, Etodolac, physiology. The stomach is richly endowed with a Fenclofenac multilayered protective barrier which includes 17,20 d. Indole derivatives : Indomethacin, Sulindac • A thick layer of hydrophobic mucous. e. Oxicam derivative : Piroxicam • Substantial glutathione to scavenge any 4. Cox-2 Inhibitors : Celecoxib, Etoricoxib, superoxide radicals generated. Meloxicam • Bicarbonate secreted by the superficial lining Adverse effects cells which serves to buffer acid that penetrates The widespread use of these drugs has led to the through the mucous barrier. recognition of numerous associated adverse effects. The most important complications are: • Tight junctions between cells of the superficial lining. Gastroduodenal toxicity • A significant blood supply, which maintains the NSAIDs can induce both unimportant and important highly metabolic activity of the superficial lining, effects in the gastroduodenum 14-22. A variety of cells. symptoms and signs are commonly associated with NSAID-induced gastrointestinal toxicity. In addition, prostaglandins modulate the amount of gastric acid generated, regulate the integrity of the • Dyspepsia – Some believe that dyspepsia is the mucous barrier, the amount of bicarbonate and most common problem, affecting up to 50 glutathione generated, and the amount of mucosal 21 JM Vol. 7, No. 1 Non Steroidal Anti Inflammatory-An Overview blood flow. Thus, it is not surprising that ulcer are also infected with Helicobacter pylori. There prostaglandin inhibition by a NSAID might lead to is little correlation between the majority of gastrointestinal toxicity. symptoms induced by NSAIDs and pathologic changes 24. However, local esophageal disease due to NSAIDs The NSAIDs are all weak organic acids except for appears to be correlated with symptoms 25. nabumetone. As a result, most of the NSAIDs that are not enteric coated are uncharged in the acid Risk of gastrointestinal toxicity – One important milieu of the stomach lumen. They are therefore determinant is the duration of therapy. The able to rapidly penetrate the hydrophobic mucous administration of NSAIDs for a short period of time barrier and enter the superficial lining cells 17,20. (less than one week) in healthy people is unlikely to Inhibition of prostaglandin synthesis in the mucosa result in any significant gastroduodenal toxicity 25- allows these drugs to degrade the integrity of the 30. In contrast, longer duration of therapy is barrier that normally prevents gastric acid from associated with an increased risk of developing reaching the cells, to reduce