Acetaminophen toxicity91.8.10
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Acetaminophen toxicity can cause liver damage and failure if too much is ingested. It is metabolized in the liver and toxic metabolites can accumulate if pathways are saturated from overdose. Treatment involves assessing risk using a nomogram plotting acetaminophen levels drawn 4 hours after ingestion. N-acetylcysteine is given if above the risk line to replenish glutathione and prevent toxicity. It is administered orally or intravenously in a multi-dose regimen over days. Outcomes depend on prompt treatment to prevent liver failure and possible need for transplant.
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Acetaminophen toxicity91.8.10
- 1. Acetaminophen Toxicity BY : MOHAMED RAMEEZ ASLAM SUJAH 5TH YR TSMU 1
- 2. Pharmacokinetics • Absorption – Rapidly absorbed from the GI tract – Peak concentration usually occurs between 60 and 120 minutes – Peak plasma levels almost always occur within 4 hours
- 3. Distribution • Vd 1.0 - 2.0 L/Kg • Approximately 20% plasma protein bound may increase to 50% in overdose • Has been reported to cross the placenta
- 6. Half life • Average 2 hours – range 0.9 to 3.25 hours • No age related differences • No change in patients with renal disease • With liver dysfunction, may increase to 17 hours
- 7. Risk factors • • • • Chronic excessive alcohol consumtion Fasting Isoniazid usage Antiepileptics (carbamazepine,phenytoin and barbiturates) 7
- 8. Toxicity • Factors involved in predicting hepatotoxicity – – – – – total quantity ingested time from ingestion to treatment age of the patient alcoholism enzyme inducing medications
- 9. • Toxic dose – In adults, threshold for liver damage is 150 to 250 mg/kg – Children under 10 appear to be more resistant
- 10. • Potential liver damage – Adults: > 150 mg/kg in acute dose – Adults: > 7.5 Grams in 24 hours (chronic) – Children (<10 yrs): > 200 mg/kg
- 11. 4 Stages of Acetaminophen Poisoning • Phase I (30 minutes to 24 hours) – Within a few hours after ingestion, patients experience anorexia, nausea, pallor, vomiting, and diaphoresis. Malaise may be present. Patient may appear normal
- 12. • Phase II (24 to 48 hours) – clinical signs of hepatotoxicity. – Right upper quadrant pain due to hepatic damage – hepatomegaly, AST/ALT/bill/lipase elevation. – Prothrombin times may be prolonged – Renal function may begin to deteriorate.
- 13. • Phase III (3 to 5 days) – Fulminant hepatic failure +/- death – Associated lactic acidosis, coag-ulopathy, encephalopathy; possible pancreatitis, hypoglycemia, jaundice, and renal failure . – Marked elevation of liver enzymes (with AST typically >3,000), – Elevation of NH3, coags, lactate Characterized by symptoms of hepatic necrosis.
- 14. • Phase IV (4 days to 2 weeks) – Complete resolution or death
- 15. Symptoms Stage Time Labs I ½ –24 hrs Usually normal N/V, pallor, lethargy II 24-72 hrs Coags out, AST/ALT up by 36 hrs, incr Cr Initially improve, then RUQ pain, HM III 72-96 hrs Abnormalities peak Jaundice, confusion, bleeding, N/V IV 4d-2 wks Slow return to normal (if pt survives) recovery
- 16. Treatment • GI decontamination – Syrup of Ipecac • return usually 30-40% at best • best if used early (first 1-2 hours) – Gastric lavage • effectiveness diminishes with time
- 17. • Activated charcoal – Most effective method – Dose 50-100 Grams • Cathartic – Utilized to speed transit time
- 18. Extracorporeal elimination • Hemodialysis – Limited benefit – Damage occurs quickly • Hemoperfusion – No benefit • Peritoneal dialysis – No benefit
- 19. • 4 hour post ingestion Acetaminophen level – levels drawn earlier may be erroneous – levels may be accurate out to 18 hours
- 20. • Plot level on Rumack-Matthews nomogram –150 mg/dl at 4 hours is possibly toxic – Do not use therapeutic “normal” values to determine potential toxicity!
- 21. Rumack and Matthew Nomogram 500 Late 150 100 50 Not valid after 24 hours 10 5 mcg/ml 4 8 12 16 20 Hours After Acetaminophen Ingestion 24
- 22. Also management based on • Baseline CBC • creatinine, BUN, blood sugar, electrolytes • prothrombin times • AST, ALT – repeat q 24 hours – elevations typically seen 24-36 hours post ingestion
- 23. • If APAP level plots above the possible risk line administer N-acetylcysteine (NAC). • If NAC is indicated, full regimen should be followed. Do not stop NAC early if nomogram indicates toxic possibility
- 24. N-acetylcysteine (NAC) • Mechanism of action – glutathione substitute – may supply inorganic sulfur, altering metabolism • Route of administration – Orally or IV
- 25. • NAC dosing – Oral 72 hour protocol • Loading dose is 140 mg/kg • Maintenance doses: 70 mg/kg – Given every 4 hours x 17 doses starting 4 hours after loading dose
- 26. • Intravenous acetylcysteine is given as a continuous infusion over 20 hours for a total dose 300 mg/kg • Recommended administration involves infusion of a 150 mg/kg loading dose over 15 to 60 minutes, followed by a 50 mg/kg infusion over four hours; the last 100 mg/kg are infused over the remaining 16 hours of the protocol 26
- 27. • NAC supplied as 10 or 20% oral solution – dilute to 5% final concentration with juice or soft drink – May be administered via NG tube – If emesis occurs within 1 hour of administration, repeat the dose
- 28. • If emesis persists, antiemetics may be used – (metoclopramide) • 0.1 to 1.0 mg/kg iv is often effective – If emesis is refractory, may consider (ondansetron) or ® (granisetron) • Expensive, but very effective
- 29. Pediatric overdoses • More resistant to toxicity vs. adults – if a child plots in the possible risk category on the Rumack nomogram, do not resist using NAC because of this greater tolerance to APAP – Administer full course of NAC if nomogram indicates that it is needed
- 30. Special considerations with NAC • NAC administered on basis of nomogram plot • if initial level indicates need for NAC do not discontinue
- 31. NAC side effects • Relatively free of side effects when given orally • Emesis may occur – extremely offensive sulfur odor
- 32. Liver transplant • In patients who develop fulminant hepatic failure › an arterial blood pH less than 7.3 after fluid resusiation › if a patient has Grade III or IV encephalopathy › a prothrombin time greater than 100 seconds, and a serum creatinine greater than 300 mmol/L In a 24 hour period
- 33. ED Admission Estimate time of ingestion Less than 4 hours since overdose Less than 2 hours since overdose More than 2 hours since overdose Gastric emptying 4 or more hours since overdose Activated charcoal Activated charcoal Draw blood plasma 4 hours after overdose for plasma acetaminophen assay Acetaminophen concentration available within 8 hours of overdose Wait for acetaminophen assay result Draw blood ASAP for plasma acetaminophen assay Acetaminophen concentration not available within 8 hours of overdose Start NAC pending assay result Loading does: 140 mg/kg APAP level below risk line on nomogram APAP level on or above risk line DC NAC if started Treat with full course of NAC No further medical management needed Daily LiverFT’s, prothrombin times Treat other med or psychiatric problems Provide supportive care