Non-steroidal antiinflammatory drugs (NSAIDs) R. B. Janani Buddhika Dept. of Health Sciences The Open University of Sri Lanka
Non-Steroidal Anti-inflammatory Drugs (NSAIDs) Used in mild to moderate pain Provide symptomatic relief from pain & swelling in, chronic joint disease - osteo- & rheumatoid arthritis acute inflammatory conditions - sport injuries fractures, sprains & other soft tissue injuries postoperative pains dental & menstrual pain pain of headaches & migraine
(NSAIDs) cont. Often taken without prescription for other types of minor aches & pains Different formulations -tablets, injections, gels All NSAIDs, particularly the 'classic' NSAIDs, can have significant unwanted effects- especially in elderly Newer agents- fewer adverse actions
MECHANISM OF ACTION OF NSAIDs
NSAIDs - Mechanism of action NSAIDs are inhibitors of cyclooxygenase Most NSAIDs inhibit both cox1 & cox2 iso enzymes Cyclooxygenases catalyse the formation of prostaglandins (PG) & thromboxanes from arachidonic acid Therefore NSAIDs inhibit the formation of prostaglandins & thromboxanes (TX) from arachidonic acid
NSAIDs - Mechanism of action cont. Reduced synthesis of PGE2 & PGF2 is associated with their anti inflammatory action Reduced thromboxane synthesis is associated with platelet aggregation & adhesiveness NSAIDs does not inhibit lipoxygenase NSAIDs does not alter production of leukotrienes
Membrane phospholipids For Maintenance Arachidonic acid In Induced situations COX-1 COX-2 NSAIDs Coxibs thromboxane / prostaglandins prostaglandins Primarily support platelet function Primarily protect GI mucosa Primarily mediate inflammation, pain & fever
NSAIDs - Mechanism of action cont. Aspirin and traditional NSAIDs inhibit both COX 1 & COX 2 Prostaglandin Local hormones produced in body, have diverse effects in the body Transmit pain information to the brain Modulate hypothalamic thermostat & inflammation Thromboxane Responsible for aggregation of platelets from blood clots
For understanding the concept Prostaglandins, & the related compounds thromboxanes & leukotrienes collectively known as eicosanoids to reflect their origin from polyunsaturated fatty acids with 20 carbons extremely potent compounds that elicit a wide range of responses, both physiologic & pathologic produced in very small amounts in almost all tissues rather than in specialized glands act locally not stored short half-life as rapidly metabolized to inactive products
For understanding the concept Inhibition of prostaglandin synthesis by a number of unrelated compounds Cortisol (a steroidal anti-inflammatory agent) inhibit phospholipase A 2 activity (therefore arachidonic acid, precursor of the prostaglandins,is not available) NSAIDS inhibit both COX-1 and COX-2 and, therefore, prevent the synthesis of the parent prostaglandin, PGH 2. [Note: Systemic inhibition of COX-1, with subsequent damage to the stomach and the kidneys, and impaired clotting of blood, is the basis of aspirin's toxicity.] Inhibitors specific for COX-2 (for example, celecoxib) reduce pathologic inflammatory processes while maintaining the physiologic functions of COX-1; however, their use has been associated with increased risk of heart attacks.
COX-1 (synthesized in normal physiological conditions) a constitutive enzyme (constantly produced by cells) expressed in most tissues (esp. GI, kidneys, endothelial cells) & blood platelets COX-1 required for maintenance of healthy gastric tissue renal homeostasis platelet aggregation required for maintenance of tissue homeostasis initiation of delivery
COX-2 - (synthesized especially in pathological conditions) found in brain, bone, kidneys, GI tract, & the female reproductive system responsible for production of prostanoid mediators of inflammation COX-2 - inducible in a limited number of tissues in response to products of activated immune & inflammatory cells increase in prostaglandin synthesis subsequent to the induction of COX-2 mediates the pain, heat, redness, & swelling of inflammation, & the fever of infection.
COX-3 Discovered in 2002.
PHARMACOKINETICS
Pharmacokinetics Most NSAIDs are weak acids Well absorbed from the stomach & intestinal mucosa Do not undergo 1 st pass metabolism Highly plama protein bound(>95%) usually to albumin. Vd small Most NSAIDs are metabolised in liver By oxidation & conjugation to inactive metaboiltes Excreted in urine
PHARMACOLOGICAL ACTIONS
Pharmacological actions NSAIDs 3 major pharmacologically desirable actions, An anti-inflammatory action: Decrease in prostaglandin E2 & prostacyclin reduces vasodilatation &, indirectly, oedema Accumulation of inflammatory cells is not reduced An analgesic effect: Decrease prostaglandin generation means less sensitisation of nociceptive nerve endings to inflammatory mediators such as bradykinin and 5-hydroxytryptamine Relief of headache by decreasing prostaglandin-mediated vasodilatation
Pharmacological actions NSAIDs cont. An antipyretic effect: interleukin-1 releases prostaglandins in the CNS, where they elevate the hypothalamic set point for temperature control causing fever. NSAIDs prevent this.
Pharmacological actions NSAIDs cont. In addition to the desirable pharmacological effects, all the NSAIDs have, to a greater or lesser degree, the same types of mechanism-based side effects. gastric irritation- from simple discomfort to ulcer formation effect on renal blood flow in the compromised kidney tendency to prolong bleeding - by inhibition of platelet function
Clinical uses of NSAIDs For analgesia e.g. headache, dysmenorrhoea, backache, postoperative pain Short-term use- Aspirin, paracetamol or ibuprofen Chronic pain: more potent, longer lasting drugs e.g. naproxen, piroxicam To reduce the requirement for narcotic analgesics e.g. ketorolac postoperatively To lower temperature (antipyretic): paracetamol For anti-inflammatory effects e.g. rheumatoid arthritis and related connective tissue disorders, gout & soft tissue disorders Note -there is substantial individual variation in clinical response to NSAIDs and considerable unpredictable patient preference for one drug rather than another.
ADVERSE EFFECTS
Unwanted effects of NSAIDs By inhibition of the constitutive housekeeping enzyme cyclo-oxygenase (COX)-1 isoform of COX, are common, particularly in the elderly 1. Gastrointestinal Side Effects- Dyspepsia, nausea & vomiting. Gastric damage - chronic users, with risk of haemorrhage. The cause is suppression of gastroprotective prostaglandins in the gastric mucosa. 2. Reversible renal insufficiency. When the compensatory prostaglandin E2-mediated vasodilatation is inhibited. 3. Skin reactions. Mechanism unknown.
Unwanted effects of NSAIDs cont. 4. 'Analgesic-associated nephropathy'. Due to long-continued high doses of NSAIDs (e.g. paracetamol) and is often irreversible. 5. Liver disorders, bone marrow depression. Relatively uncommon. 6. Bronchospasm - in 'aspirin-sensitive' asthmatics.
1. GI side effects Commonest side effect of NSAIDs Inhibition of gastric COX-1, responsible for synthesis of prostaglandins that normally inhibit acid secretion & protect the mucosa Common GI side effects, gastric discomfort, dyspepsia, diarrhoea, nausea & vomiting, gastric bleeding and ulceration Oral administration of prostaglandin analogues (misoprostol) can diminish gastric damage produced by NSAIDs.
2. Renal side effects Therapeutic doses in, Healthy individuals - little threat to kidney function Susceptible patients - cause acute renal insufficiency, reversible on stopping the drug NSAIDs inhibit biosynthesis of prostanoids (PGE2 & PGI2; prostacyclin). Prostaglandins (esp. PGE2 ) normally cause vasodilation of afferent arterioles of glomeruli This helps to maintain normal glomerular perfusion & glomerular filtration rate (GFR) NSAIDs block this effect and may cause renal impairment.
2. Renal side effects cont. Patients at risk Neonates & elderly Patients with heart, liver or kidney disease, or a reduced circulating blood volume Chronic NSAIDs consumption May cause analgesic nephropathy characterized by chronic nephritis and renal papillary necrosis
NSAIDs in Pregnancy & Lactation Contra-indicated during pregnancy, labour & delivery esp. ketorolac (particularly in 3 rd trimester) May cause closure of ductus arteriosus & impaired fetal circulation Use of NSAIDs & aspirin late in pregnancy may increase the risk of postpartum hemorrhage.
Drug Interactions Concomitant NSAIDs & Low-Dose Aspirin Classic NSAIDs or COX-2 inhibitors with "cardioprotective" lowdose aspirin may increase the likelihood of GI adverse effects. This interaction should not occur with selective COX-2 inhibitors, because mature human platelets lack COX-2. Other Drug Interactions NSAIDs & ACEI NSAIDs may reduce the effectiveness of ACE inhibitors by blocking the production of vasodilator & natriuretic prostaglandins. Can produce marked bradycardia NSAIDs & corticosteroids May increase the frequency or severity of GI ulceration
Drug Interactions cont. NSAIDs & warfarin Increase the risk of bleeding NSAIDs & high plasma protein bound drugs Many NSAIDs are highly bound to plasma proteins and thus may displace other drugs from their binding sites. Dose of such agents may require to adjust to prevent toxicity
SOME IMPORTANT NSAIDS
Cyclo-oxygenase-inhibitory specificity of some common non-steroidal anti-inflammatory drugs & coxibs Group Examples COX-1 Highly COX-1-selective Ketorolac Non selective COX-2 Weakly COX-1- selective Non-selective; full inhibition of both enzymes Non-selective; incomplete inhibition of both enzymes Weakly COX-2- selective Very COX-2-selective Indometacin, aspirin, naproxen, ibuprofen Fenoprofen Salicylate Diflunisal, piroxicam, meclofenamate, diclofenac, celecoxib Valdecoxib, etoricoxib
Aspirin (acetylsalicylic acid) Oldest non-steroidal anti-inflammatory drug Irreversibly inactivate both cyclo-oxygenase (COX)-1 & COX-2 anti-inflammatory action inhibits platelet aggregation main clinical importance -in the therapy of myocardial infarction
Aspirin Pharmacokinetics It is given orally and is rapidly absorbed; 75% is metabolised in liver Elimination follows first-order kinetics with low doses (halflife 4 hours), and saturation kinetics with high doses (halflife over 15 hours)
Aspirin - MOA Mechanism of action Irreversibly inactivate cox enzymes. Aspirin irreversibly inhibits cox1 and modifies the enzymatic activity of cox2 Aspirin acts as an acetylating agent and it covalently attaches its acetyl group to serine residue in the active site of the cox enzyme. This makes aspirin different from other NSAIDs (such as diclofenac and Ibuprofen which are reversible inhibitors)
Aspirin (acetylsalicylic acid) cont. Unwanted effects with therapeutic doses: some gastric bleeding with large doses: dizziness, deafness & tinnitus ('salicylism'); compensated respiratory alkalosis may occur with toxic doses (e.g. from self-poisoning): uncompensated respiratory acidosis with metabolic acidosis may occur, in children - Reye's syndrome concomitant use with warfarin, can cause a potentially hazardous increase in the risk of bleeding
PARACETAMOL
Paracetamol Has potent analgesic and antipyretic actions Weaker anti-inflammatory effects than other NSAIDs. May act through inhibition of a central nervous systemspecific cyclo-oxygenase (COX) isoform such as COX-3, although this is not yet conclusive. Given orally Metabolised in the liver (half-life 2-4 hours).
Paracetamol cont. Toxic doses -cause nausea and vomiting after 24-48 hours-potentially fatal liver damage by saturating normal conjugating enzymes, causing the drug to be converted by mixed function oxidases to N-acetyl-p-benzoquinone imine. If not inactivated by conjugation with glutathione, this compound reacts with cell proteins and kills the cell. Agents that increase glutathione (intravenous acetylcysteine or oral methionine) can prevent liver damage if given early.
Agents selective for cyclo-oxygenase-2 Eg. Celecoxib, etoricoxib Several have been withdrawn, & overall licensing situation is volatile Current advice restricts the use of coxibs to patients for whom treatment with conventional NSAIDs would pose a high probability of serious gastrointestinal side effects, and Coxibs are adviced to prescribed only after an assessment of cardiovascular risk
Other NSAIDs Indomethacin Diclofenac Ibuprofen Mefanamic acid
Indomethacin Prominent antiinflammatory & analgesic-antipyretic properties similar to those of the salicylates (as asprin) More potent inhibitor of the cyclooxygenases than is aspirin but patient intolerance generally limits its use to short-term dosing Inhibits the motility of polymorphonuclear leukocytes & depresses the biosynthesis of mucopolysaccharides Uses - relieving joint pain, swelling, & tenderness, increasing grip strength
Diclofenac Analgesic, antipyretic, & antiinflammatory effect Potency against COX-2 is greater than that of indomethacin, naproxen, or several other classic NSAIDs Reduce intracellular concentrations of free AA in leukocytes Selectivity of diclofenac for COX-2 resembles that of celecoxib
Oxicams- Enolic Acids Eg. Piroxicam, Meloxicam Inhibit COX-1 and COX-2 Have anti-inflammatory, analgesic,& antipyretic activity Generally nonselective COX inhibitors But one member (meloxicam) shows modest COX-2 selectivity comparable to celecoxib Similar in efficacy to aspirin, indomethacin, or naproxen for the long-term treatment of rheumatoid arthritis or osteoarthritis Long half-life - once-a-day dosing
References: 1. Pharmacology by M. P. Rang, M. M. Dale, & J. M. Ritter. 2. Goodman and Gilman 11th edition
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