Emergency Medicine

170 Tox icolog y

SPECIFIC POISONS

Paracetamol

DIAGNOSIS

1 Paracetamol overdose is common and potentially lethal.

2 Hepatocellular necrosis is the major complication of paracetamol toxicity.

Factors that enhance the potential for hepatotoxicity, and therefore morbid-

ity and mortality, include:

(i) Late presentation with delayed antidote administration,

especially if over 24 h.

(ii) Staggered overdose: multiple supra-therapeutic ingestions over a

number of days.

(iii) Glutathione deficiency in starvation and debilitating illness such

as AIDS.

(iv) Enzyme-inducing drugs such as carbamazepine, phenobarbitone

(phenobarbital), rifampicin or isoniazid.

(v) Regular alcohol use.

3 Determine the time since ingestion, total paracetamol consumed and the

patient’s weight:

(i) Patients who have taken >10 g (20 tablets) or >200 mg/kg over a

period of <8 h are considered at risk from severe liver damage.

(ii) The greatest risk of hepatotoxicity is related to the extent of delay

beyond 8 h until antidote treatment with N-acetylcysteine (NAC)

is commenced.

(iii) Hepatotoxicity may also occur in patients who take repeated or

staggered doses, or sustained-release preparations.

4 The patient is usually asymptomatic, but can present in fulminant hepatic

failure with abdominal pain, vomiting, hypoglycaemia, tender hepato-

megaly, jaundice and encephalopathy.

5 Gain i.v. access and send bloods for full blood count (FBC), urea and

electrolytes (U&Es), liver function tests (LFTs), prothrombin index (PTI)

(international normalized ratio [INR]) and a blood sugar level.

(i) These bloods become more important if the patient presents over

8 h after ingestion, and are essential if presentation is delayed

beyond 24 h or more.

(ii) Send a paracetamol level once 4 h or more have elapsed since

overdose.

MANAGEMENT

1 Resuscitation is rarely required unless the patient is in fulminant hepatic

failure.

(i) Administer 50% dextrose 50 mL i.v. if the patient is

hypoglycaemic.