2612 Acetaminophen Acetaminophen, also known as paracetamol, is commonly used for its analgesic and antipyretic effects. Its therapeutic effects are similar to salicylates, but it lacks anti-inflammatory, antiplatelet, and gastric ulcerative effects. The excellent tolerability of therapeutic doses of paracetamol (acetaminophen) is a major factor in the very wide use of the drug. The major problem in the use of paracetamol is its hepatotoxicity after an overdose. Hepatotoxicity has also been reported after therapeutic doses, but critical analysis indicates that most patients with alleged toxicity from therapeutic doses have taken overdoses. Importantly, prospective studies indicate that therapeutic doses of paracetamol are an unlikely cause of hepatotoxicity in patients who ingest moderate to large amounts of alcohol. (A7820). Single doses of paracetamol are effective analgesics for acute postoperative pain and give rise to few adverse effects. (A7821). Acetaminophen (AAP) overdose and the resulting hepatotoxicity is an important clinical problem. In addition, AAP is widely used as a prototype hepatotoxin to study mechanisms of chemical-induced cell injury and to test the hepatoprotective potential of new drugs and herbal medicines. Because of its importance, the mechanisms of AAP-induced liver cell injury have been extensively investigated and controversially discussed for many years. (A7822). 103-90-2 1983 C8H9NO2 151.063330 White powder. 169-171°C 1.4E+004 mg/L (at 25°C) Oral, rapid and almost complete. Paracetamol toxicity is one of the most common causes of poisoning worldwide. The toxic effects of acetaminophen are due to a minor alkylating metabolite (N-acetyl-p-benzo-quinone imine – also known as NAPQI), not acetaminophen itself nor any of the other major metabolites. Cytochromes P450 2E1 and 3A4 convert approximately 5% of paracetamol to NAPQI. This toxic metabolite reacts with sulfhydryl groups on proteins and with glutathione (GSH). NAPQI depletes the liver's natural antioxidant glutathione and directly damages cells in the liver, leading to liver failure. In animal studies, hepatic glutathione must be depleted to less than 70% of normal levels before hepatotoxicity occurs. More specifically, oxidation by NAPQI of GSH to GSSG (oxidized glutathione) and the reduction of GSSG back to GSH by the NADPH-dependent glutathione reductase appear to be responsible for the rapid oxidation of NADPH that occurs in hepatocytes incubated with NAPQI. Risk factors for toxicity include excessive chronic alcohol intake, fasting or anorexia nervosa, and the use of certain drugs such as isoniazid. At usual doses, paracetamol is quickly detoxified by combining irreversibly with the sulfhydryl group of glutathione to produce a non-toxic conjugate that is eventually excreted by the kidneys. The toxic dose of paracetamol is highly variable. Acetaminophen primarily undergoes glucuronidation (45-55% of the dose) in which this process is facilitated by UGT1A1, UGT1A6, UGT1A9, UGT2B15 in the liver or UGT1A10 in the gut. 30-35% of the dose undergoes sulfation. This biotransformation is facilitated by SULT1A1, SULT1A3, SULT1A4, SULT1E1 and SULT2A1. A small percentage of acetaminophen is oxidized by CYP2E1 to form N-acetyl-p-benzo-quinone imine (NAPQI), a toxic metabolite which is then conjugated to glutathione and excreted renally. Studies suggest that CYP3A4 and CYP2E1 are the primary cytochrome P450 isozymes responsible for the generation of toxic metabolites. Accumulation of NAPQI may occur if primary metabolic pathways are saturated. Acetaminophen is metabolized primarily in the liver, where most of it is converted to inactive compounds by conjugation with sulfate and glucuronide, and then excreted by the kidneys. Only a small portion is metabolized via the hepatic cytochrome P450 enzyme system. The toxic effects of acetaminophen are due to a minor alkylating metabolite (N-acetyl-p-benzo-quinone imine), not acetaminophen itself nor any of the major metabolites. This toxic metabolite reacts with sulfhydryl groups. At usual doses, it is quickly detoxified by combining irreversibly with the sulfhydryl group of glutathione to produce a non-toxic conjugate that is eventually excreted by the kidneys. The toxic dose of paracetamol is highly variable. Route of Elimination: Approximately 80% of acetaminophen is excreted in the urine after conjugation and about 3% is excreted unchanged. Half Life: 1 to 4 hours LD50: 338 mg/kg (Oral, Mouse) (A308) LD50: 1944 mg/kg (Oral, Rat) (A308) In adults, single doses above 10 grams or 200 mg/kg of bodyweight, whichever is lower, have a reasonable likelihood of causing toxicity. 25 g for an adult human. (A308) 3, not classifiable as to its carcinogenicity to humans. (L135) An over-the-counter analgesic (pain reliever) and antipyretic (fever reducer). It is commonly used for the relief of fever, headaches, and other minor aches and pains, and is a major ingredient in numerous cold and flu remedies. Skin rashes, blood disorders and a swollen pancreas have occasionally happened in people taking the drug on a regular basis for a long time. When taken at the recommended dose, side-effects of paracetamol are rare. Skin rashes, blood disorders and a swollen pancreas have occasionally happened in people taking the drug on a regular basis for a long time. The signs and symptoms of paracetamol toxicity occur in three phases. The first phase begins within hours of overdose, and consists of nausea, vomiting, pallor, and sweating. Rarely, after massive overdoses, patients may develop symptoms of metabolic acidosis and coma early in the course of poisoning.The second phase occurs between 24 and 72 hours following overdose and consists of signs of increasing liver damage. In general, damage occurs in hepatocytes as they metabolize the paracetamol. The individual may experience right upper quadrant pain. Acute kidney failure may also occur during this phase, typically caused by either hepatorenal syndrome or multiple organ dysfunction syndrome. The third phase follows at 3 to 5 days, and is marked by complications of massive hepatic necrosis leading to fulminant hepatic failure with complications of coagulation defects, hypoglycemia, kidney failure, hepatic encephalopathy, cerebral edema, sepsis, multiple organ failure, and death. In adults, the initial treatment for paracetamol overdose is gastrointestinal decontamination. Paracetamol absorption from the gastrointestinal tract is complete within two hours under normal circumstances, so decontamination is most helpful if performed within this timeframe. Gastric lavage, better known as stomach pumping, may be considered if the amount ingested is potentially life-threatening and the procedure can be performed within 60 minutes of ingestion. Acetylcysteine, when used early in the course of treatment, reduces morbidity and virtually eliminating mortality associated with even a massive acetaminophen overdose. (L1712) In patients who develop fulminant hepatic failure or who are otherwise expected to die from liver failure, the mainstay of management is liver transplantation. 2009-07-05T03:31:24Z 2014-12-24T20:25:43Z Acetaminophen C06804 2386 CPD-7669 D000082 Paracetamol DB00316 TYL 7 true CC(O)=NC1=CC=C(O)C=C1 C8H9NO2 InChI=1S/C8H9NO2/c1-6(10)9-7-2-4-8(11)5-3-7/h2-5,11H,1H3,(H,9,10) InChIKey=RZVAJINKPMORJF-UHFFFAOYSA-N 151.1626 151.063328537 Exogenous Solid 0.46 HMDB01859 CHEMBL112 1906 <p>Jeffrey L. Finnan, Rudolph E. Lisa, Douglass N. Schmidt, &#8220;Process for preparing spray dried acetaminophen powder and the powder prepared thereby.&#8221; U.S. Patent US4710519, issued October, 1975.</p>