B. Prothrombin time – Explanation

An elevated prothrombin time signifies liver failure in paracetamol overdose and is a marker of poor
prognosis. However, arterial pH, creatinine and encephalopathy are also markers of a need for liver
transplantation
Paracetamol overdose: management

Management
The following is based on the current BNF guidance. The National Poisons Information
Service/TOXBASE should always be consulted for situations outside of the normal parameters.

Activated charcoal should be given if:

• paracetamol dose is in excess of 150 mg/kg (75 mg/kg if high-risk, see below) or 12 g, whichever is
  the smaller, and;
• the paracetamol was ingested in the previous hour

Patients presenting within 8 hours

• paracetamol levels (along with U&Es, LFTs and prothrombin time) should be checked 4 hours after
  ingestion (earlier samples may be misleading)
• the value should be plotted on a paracetamol treatment graph (see below)
• if the value is above the relevant treatment line intravenous acetylcysteine should be given

Patients presenting 8-24 hours after ingestion

• take an immediate blood sample for paracetamol levels, U&Es, LFTs and prothrombin time
• start acetylcysteine immediately if it is thought that more than 150 mg/kg body weight has been
  ingested. If the high risk (see below) consider treatment at a lower dose (75 mg/kg)
  xotherwise wait for the paracetamol leve, give intravenous acetylecysteine if the value is above the
  relevant treatment line.

The following groups of patients are at an increased risk of developing hepatotoxicity following a
paracetamol overdose and hence are considered ‘high-risk’:

• patients taking liver enzyme-inducing drugs (rifampicin, phenytoin, carbamazepine, chronic alcohol
  excess, St John’s Wort)
• malnourished patients (e.g. anorexia or bulimia, cystic fibrosis, hepatitis C, alcoholism, HIV
• patients who have not eaten for a few days

King’s College Hospital criteria for liver transplantation (paracetamol liver failure) Arterial pH < 7.3, 24 hours after ingestion or all of the following: prothrombin time > 100 seconds creatinine > 300 μmol/l grade III or IV encephalopathy