Acetaminophen toxicity/overdose

The answer is c. (Hardman, pp 632-633.) Nausea, vomiting, abdominal pain, and diarrhea are early signs of the severe liver toxicity caused by high levels of acetaminophen other symptoms of acetaminophen toxicity include dizziness, excitement, and disorientation. N-acetyl-L-cysteine is the appropriate treatment for acetaminophen overdose. 

Large doses of acetaminophen can cause renal and hepatic toxicity in rats and mice. Toxicity is characterized by renal tubular necrosis in the proximal tubules (Schnellmann, 2001). Acetaminophen toxicity has also been reported in humans. Generally, toxicosis is a result of large overdoses which result in proximal tubular necrosis. Aspirin, ibuprofen, and acetaminophen are the important analgesics, which are reported to cause toxicosis in veterinary medicine. Renal lesions including renal tubular necrosis and papillary necrosis have been reported in dogs. 

A large body of evidence is available examining the acute toxicity of acetaminophen in animal models. Mice and rats have been widely used to study the toxic effects of acetaminophen. Since the rat is relatively resistant, the mouse has been the most widely used species to study both the mechanisms of acetaminophen toxicity and to examine chemicals that potentiate or protect from the toxicity. Hepatotoxic-ity and nephrotoxicity are the two main effects associated with acute overdose of acetaminophen. Of these, death in most species is due to acute hepatic failure. LD50 values range from 350 to 4500mgkg depending on the species and the route of acetaminophen administration, mice (LD50 350-... 

Another issue is drug metabolism and toxicity. Acetaminophen overdose remains a major cause of liver failure in the United States. Several P450s are involved in the oxidation to the reactive imi-noquinone . Studies with P450 2E1 knockout mice indicate that P450 2E1 is a major determinant of acetaminophen toxicity, because the toxicity was considerably attenuated in null animals ... 

Acetaminophen (paracetamol) is a commonly used analgesic which is hepatotoxic at high doses in humans and in laboratory animals. Toxicity is believed to be mediated by the reactive metabolite N-acetyl-p-benzoquinone imine which binds to protein thiols as 3-(cystein-S-yl)acetaminophen adducts. Ultrasensitive immimoassays for 3-(with parallel elevations in serum adducts and serum levels of the liver-specific transaminase ALT. This suggested that the serum adducts were of hepatic origin and could be monitored as a biomarker of acetaminophen toxicity. Analysis of serum samples from acetaminophen overdose patients demonstrated a positive correlation between immunochemically detectable serum adducts and hepatotoxicity. 

Chronic ethanol use increases the risk of hepatotoxicity when acetaminophen is used in high doses however, acute ingestion of alcohol along with an acetaminophen overdose decreases the toxicity of acetaminophen. 

Acetaminophen is usually well tolerated, but potentially fatal hepatotoxicity with overdose is well documented. It should be used with caution in patients with liver disease and those who chronically abuse alcohol. Chronic alcohol users (three or more drinks daily) should be warned about an increased risk of liver damage or GI bleeding with acetaminophen. Other individuals do not appear to be at increased risk for GI bleeding. Renal toxicity occurs less frequently than with NSAIDs. 

Acetaminophen overdose Initially 140 mg/kg, then 70 mg/kg q4h orally x 17 doses. All 17 doses must be given, even if acetaminophen levels have declined to non-toxic range. 

Tylenol CH3CONHC6H4OH N-acetyl-p-aminophenol (acetaminophen, APAP) colourless, slightly bitter crystals can be toxic if an overdose is taken pain reliever (analgesic)... 

Used in mild-to-moderate pain May use in conjunction with opioid agents to decrease doses ot each Regular alcohol use and high doses of acetaminophen may result in liver toxicity Care must be exercised to avoid overdose when combination products containing these agents ate used Drug ot choice in severe pain Use immediate-release product with SR product to control breakthrough pain in cancer patents... 

Cytochrome P-450 and cysteine conjugate p-lyse are primarily localized in the proximal tubules, and these enzymes also contribute to the susceptibility of the proximal tubule to toxicant injury. Specifically, widely used industrial solvents such as chloroform produce tubular nephrotoxicity via cytochrome P-450 activation, and haloaUcanes and haloalkenes (e.g. trichloroethylene) are rendered toxic by cysteine conjugate (3-lyse activation [24,24a]. In addition, overdoses of acetaminophen (APAP) cause nephrotoxicity that is characterized by proximal tubular necrosis [25]. APAP undergoes cytochrome P-450-mediated activation to produce a toxic electrophile, N-acetyl-p-benzoquinon-eimine (NAPQI) [25a]. Although NAPQI is extremely reactive, it is detoxified by conjugation with reduced GSH unless NAPQI is formed in excess of the cellular capacity for GSH conjugation. The excess NAPQI is available to bind to critical cellular proteins and to induce oxidative stress, resulting in disruption of cellular homeostasis and tubular injury [26]. 

A special mention of interaction of acetaminophen with alcohol consumption is warranted. Large numbers of reports in scientific literature and public media suggest that a potentially high risk of liver toxicity due to acetaminophen exists when consumed following alcohol intake. In a recent review, however. Dr. Barry Rumack suggests that only chronic heavy drinkers may be at greater risk following an overdose of acetaminophen and that no potentiation of toxicity occurs at therapeutic doses. 

N-Acetylcysteine is used primarily in the treatment of acetaminophen overdose and/or toxicity. It is also nebulized for mucolytic effects and less often used to treat corneal ulcers. It has a very low potential to cause acute toxicity in either animals or humans. 

CNS depression is the most frequently reported clinical effect. The typical overdose patient may present with extreme somnolence that may progress to frank coma. Miosis is usually present unless the individual is acidotic or has suffered hypoxic brain injury. Respiratory depression can occur and may progress to respiratory arrest. Pulmonary edema may be seen. Bradycardia, hypotension, and hyperthermia can develop. Hydrocodone is often combined in products with acetaminophen therefore, patients should be evaluated for hepatotoxicity secondary to acetaminophen overdose. Available opiate immunoassays cross-react unreliably with hydrocodone. Peak therapeutic serum levels are 0.024 mg 1 toxic levels have been reported to reach 0.1-1.3 pgml , but are of little prognostic or therapeutic value. 

Acute overdose with acetaminophen (>300 mg kg ) results in hepatotoxicity and/or nephrotoxicity. Although hepatotoxicity is frequently the predominant toxicity, acetaminophen nephrotoxicity can occur in the absence of marked hepatic toxicity. In these cases, liver function returns to normal or near normal levels before the onset of nephrotoxicity. Acute acetaminophen nephrotoxicity is generally characterized as oliguric acute renal failure with acute tubular necrosis. Acetaminophen can also induce acute nephrotoxicity in therapeutic doses, but chronic alcohol intake usually accompanies renal toxicity in these patients. 

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