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Elijah Bailey
Elijah Bailey

Mechanism Of Action Of Paracetamol Pdf Free


According to its FDA labeling, acetaminophen's exact mechanism of action has not been fully establishedLabel - despite this, it is often categorized alongside NSAIDs (nonsteroidal anti-inflammatory drugs) due to its ability to inhibit the cyclooxygenase (COX) pathways.14 It is thought to exert central actions which ultimately lead to the alleviation of pain symptoms.14




Mechanism Of Action Of Paracetamol Pdf Free



One theory is that acetaminophen increases the pain threshold by inhibiting two isoforms of cyclooxygenase, COX-1 and COX-2, which are involved in prostaglandin (PG) synthesis. Prostaglandins are responsible for eliciting pain sensations.13 Acetaminophen does not inhibit cyclooxygenase in peripheral tissues and, therefore, has no peripheral anti-inflammatory effects. Though acetylsalicylic acid (aspirin) is an irreversible inhibitor of COX and directly blocks the active site of this enzyme, studies have shown that acetaminophen (paracetamol) blocks COX indirectly.24 Studies also suggest that acetaminophen selectively blocks a variant type of the COX enzyme that is unique from the known variants COX-1 and COX-2.6 This enzyme has been referred to as COX-3. The antipyretic actions of acetaminophen are likely attributed to direct action on heat-regulating centers in the brain, resulting in peripheral vasodilation, sweating, and loss of body heat.24 The exact mechanism of action of this drug is not fully understood at this time, but future research may contribute to deeper knowledge.24


Paracetamol is an effective analgesic and antipyretic agent, but has only weak anti-inflammatory properties. Its mechanism of action is not fully understood. It has been suggested that it may act predominantly by inhibiting prostaglandin synthesis in the CNS and to a lesser extent through a peripheral action by blocking pain-impulse generation. The peripheral action may also be due to inhibition of prostaglandin synthesis or to inhibition of the synthesis or actions of other substances that sensitise pain receptors to mechanical or chemical stimulation. Paracetamol probably produces an antipyretic action by a central effect on the hypothalamic heat-regulating centre to produce peripheral vasodilation resulting in increased blood flow through the skin, sweating and heat loss. The central action probably involves inhibition of prostaglandin synthesis in the hypothalamus. The drug has no effect on the cardiovascular and respiratory systems, and unlike salicylates it does not cause gastric irritation or bleeding.


A minor hydroxylated metabolite (N-acetyl-p-benzoquinoneimine) which is usually produced in very small amounts by mixed-function oxidases in the liver and which is usually detoxified by conjugation with liver glutathione may accumulate following paracetamol overdosage and cause liver damage. The time to peak plasma concentration of paracetamol is 0.5 to 2 hours, the time to peak effect 1 to 3 hours and the duration of action 3 to 4 hours.


In therapeutic doses paracetamol is a safe analgesic, but in overdosage it can cause severe hepatic necrosis. Following oral administration it is rapidly absorbed from the gastrointestinal tract, its systemic bioavailability being dose-dependent and ranging from 70 to 90%. Its rate of oral absorption is predominantly dependent on the rate of gastric emptying, being delayed by food, propantheline, pethidine and diamorphine and enhanced by metoclopramide. Paracetamol is also well absorbed from the rectum. It distributes rapidly and evenly throughout most tissues and fluids and has a volume of distribution of approximately 0.9L/kg. 10 to 20% of the drug is bound to red blood cells. Paracetamol is extensively metabolised (predominantly in the liver), the major metabolites being the sulphate and glucuronide conjugates. A minor fraction of drug is converted to a highly reactive alkylating metabolite which is inactivated with reduced glutathione and excreted in the urine as cysteine and mercapturic acid conjugates. Large doses of paracetamol (overdoses) cause acute hepatic necrosis as a result of depletion of glutathione and of binding of the excess reactive metabolite to vital cell constituents. This damage can be prevented by the early administration of sulfhydryl compounds such as methionine and N-acetylcysteine. In healthy subjects 85 to 95% of a therapeutic dose is excreted in the urine within 24 hours with about 4, 55, 30, 4 and 4% appearing as unchanged paracetamol and its glucuronide, sulphate, mercapturic acid and cysteine conjugates, respectively. The plasma half-life in such subjects ranges from 1.9 to 2.5 hours and the total body clearance from 4.5 to 5.5 ml/kg/min. Age has little effect on the plasma half-life, which is shortened in patients taking anticonvulsants. The plasma half-life is usually normal in patients with mild chronic liver disease, but its prolonged in those with decompensated liver disease.


It has been shown that some compounds and drugs that are often paired with antibiotics can modulate S. aureus responses that further reduces antibiotic susceptibility17,18. Nonsteroidal anti-inflammatory drugs, like acetylsalicylic acid (aspirin) and ibuprofen, can increase the inhibitory concentration of fusidic acid, an anti-staphylococcal drug17. Many other antibiotics used to treat S. aureus infections, such as beta-lactams and vancomycin, may actually promote biofilm formation6,7,8,9. Furthermore, non-antibiotic drugs like acetylsalicylic acid can even modulate biofilm generation18,19. Paracetamol, another antipyretic drug, is frequently used before and during early infection symptoms and is often given concomitantly with antibiotic treatment once infection has been confirmed. The mechanism of paracetamol remains uncertain on the molecular level and is different from acetylsalicylic acid in that it does not induce anti-inflammatory effects20,21. Until now, it has not been investigated if paracetamol has an influence on biofilm formation and development.


Currently, the mechanism of biofilm modulation by paracetamol has not been elucidated, but there are indications that an impaired iron regulation within cells may influence this phenomenon37,38, probably via iron chelation by paracetamol39. In an iron-restricted condition, biofilm and virulence factor production is increased18,40. Paracetamol has been demonstrated in vivo to reduce excess hepatic iron after administration41. In addition, a previous study on acetylsalicylic acid and biofilm showed that free Fe2+ reduction in culture media by acetylsalicylic acid, via iron chelation, could promote biofilm formation of S. aureus CC5 and CC8 strains, including Newman and USA30018. This observation suggests that iron-modulation by paracetamol may enhance S. aureus biofilm formation.


In summary, this study indicates that current clinical concentrations of an analgesic-antipyretic like paracetamol may have a role in the development and persistence of S. aureus biofilm-related infections, especially, but not limited to, strains belonging to CC8. For clinical practice our data suggest that in patients with a suspected S. aureus infection, the indication for paracetamol administration should be carefully weighed against the risk of increased biofilm formation. The mechanism of action and the effect on an established, mature biofilm by paracetamol need to be investigated in future studies.


There are several mechanisms of action that could have contributed to the positive effects of ashwagandha supplementation on resistance training and performance improvements in this study. These can be viewed from two perspectives: muscle development and muscle recovery.


The most important free radicals in many disease states are oxygen derivatives, particularly superoxide anion and the hydroxyl radical. Radical formation in the body occurs via several mechanisms, involving both endogenous and environmental factors. Superoxide anion is produced by the addition of a single electron to oxygen, and several mechanisms exist by which superoxide can be produced in vivo [3]. Some molecules such as flavine nucleotides and thiol compounds are oxidized in the presence of oxygen to produce superoxide, and these reactions greatly accelerated by the presence of transition metals such as iron or copper. The electron transport chain in the inner mitochondrial membrane performs the reduction of oxygen to water. During this process free radical intermediates are generated, which are generally tightly bound to the components of the transport chain. However, there is a constant leak of a few electrons into the mitochondrial matrix and this results in the formation of superoxide [4, 5]. There may also be continuous production of superoxide anion by vascular endothelium to neutralise nitric oxide, production of superoxide by other cells to regulate cell growth and differentiation, and the production of superoxide by phagocytic cells during the oxidative burst [6, 7].


Any biological system generating superoxide anion also occurs hydrogen peroxide as a result of a spontaneous dismutation reaction. In addition, some enzymatic reactions may produce hydrogen peroxide directly [8]. Hydrogen peroxide itself is not a free radical as it does not contain any unpaired electrons. However, it is a precursor to certain radical species such as peroxyl radical, hydroxyl radical, and superoxide. Its most vital property is the ability to cross cell membranes freely, which superoxide generally can not do. Hence, hydrogen peroxide generated in one location might diffuse a considerable distance before decomposing to yield the highly reactive hydroxyl radical, which is likely to mediate most of the toxic effects ascribed to hydrogen peroxide. Hydrogen peroxide acts as a conduit to transmit free radical induced damage across cell compartments and between cells. In the presence of hydrogen peroxide, myeloperoxidase will produce hypochlorous acid and singlet oxygen, a reaction that plays an important role in the killing of bacteria by phagocytes. Cytochrome P450 (CYP450) is a source of ROS. Through the induction of CYP450, the possibility for the production of ROS, in particular, superoxide anion and hydrogen peroxide, emerges following the breakdown or uncoupling of the CYP450 catalytic cycle. Increasing evidence has indicated that numerous drugs are metabolized by multiple activated oxygen species generated in the CYP450 catalytic cycle [9]. The hydroxyl radical or a closely related species, is probably the final mediator of most free radical induced tissue damage [10]. All of the ROS described above exert most of their pathological effects by giving rise to hydroxyl radical formation. The reason for this is that the hydroxyl radical reacts, with extremely high rate constants, with almost every type of molecule found in living cells such as lipids and nucleotides. Although hydroxyl radical formation can occur in several ways, by far the most important mechanism in vivo is likely to be the transition metal catalysed decomposition of superoxide anion and hydrogen peroxide [11]. All of elements in the first row of the d-block of the periodic table are classified as transition metals. Normally, they contain one or more unpaired electrons and are hence themselves radicals when in the elemental state. However, their main feature from the point of view of free radical biology is their inconstant valence, which allows them to undergo reactions involving the transfer of a single electron [12]. 350c69d7ab


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