Paracetamol Overdose Flashcards
What is the recommended therapeutic dose of paracetamol for an adult?
24 hours is 4 g
What is another name for paracetamol commonly used in other countries?
Acetaminophen
The National Poisons Information Service (NPIS) in the UK defines different types of paracetamol overdose (acute, staggered and therapeutic)
Briefly describe each one
Acute overdose: excessive amounts of paracetamol ingested over a period of less than 1 hour; usually in the context of self-harm
Staggered overdose: excessive amounts of paracetamol ingested over longer than 1 hour; usually in the context of self-harm
Therapeutic excess: excessive paracetamol taken with intent to treat pain or fever and without self-harm intent
Briefly describe the pathophysiology of paracetamol overdose
When the production of NAPQI exceeds the capacity to detoxify it, the excess NAPQI binds to cellular components, causing mitochondrial injury and ultimately the death of the hepatocyte. If a sufficient dose is taken, hepatocyte death may be massive and produce acute liver failure.
What are the risk factors for paracetamol overdose?
- History of self-harm
- History of frequent or repeated use of medications for pain relief
- Glutathione deficiency
- Long-term treatment with drugs that induce liver enzymes (cytochrome P450 inducers)
What are the signs of paracetamol overdose?
Examination can be normal unless signs of acute liver failure are present
- Jaundice
- Tender hepatomegaly
- Altered conscious level (hepatic encephalopathy)
- Asterixis
What are the symptoms of paracetamol overdose?
- Nausea and vomiting
- RUQ abdominal pain
What investigations should be ordered for paracetamol overdose?
- Serum paracetamol concentration
- LFTs
- Prothrombin time and INR
- Blood glucose
- Urea, creatinine and electrolytes
- Venous or arterial blood gas
- FBC
Why investigate serum paracetamol concentration? And what may this show?
- Use serum paracetamol concentration to risk-stratify the likelihood of liver injury and to determine whether treatment with acetylcysteine is needed
- May be positive
Why investigate LFTs? And what may this show?
- Suspect acute liver injury if alanine aminotransferase (ALT) is above the upper limit of normal
- May be elevated
Why investigate prothrombin time and INR? And what may this show?
- May indicate acute liver injury as prothrombin is produced by the liver
- Prothrombin time may be prolonged; INR may be increased
Why investigate blood glucose? And what may this show?
- If hypoglycaemia is present as this may indicate acute liver injury
- <3.3 mmol/L
Why investigate urea, creatinine and electrolytes? And what may this show?
- Creatinine will be raised in acute kidney injury, this may occur as part of acute liver injury (hepatorenal syndrome)
- Creatinine may be acutely elevated
Why investigate venous or arterial blood gas? And what may this show?
- A blood gas may show lactic acidosis in 2 scenarios:
- Early- lactic acidosis is commonly severe and associated with coma, most patients do not develop liver damage if treated with acetylcysteine
- Late- elevated lactate in these patients strongly predicts high mortality
Why investigate FBC? And what may this show?
- This may show leukocytosis, anaemia, or thrombocytopenia
