TOXBASEŽ - Updated 11/2005

 

Type of product:

Analgesic

 

Synonyms:

Acetaminophen

 

Ingredients:

Paracetamol
Tablet - 500 mg
Mixture - 250 mg/5 mL
Paediatric suspension - 120 mg/5 mL
Solution for infusion - 10 mg/mL (1 vial contains 100 mL)

 

Toxicity:

Risk of severe liver damage (i.e. a peak ALT more than 1000 iu/litre)
Based on the dose of paracetamol ingested (mg/kg body weight):
Less than 150 mg/kg	Unlikely
More than 250 mg/kg	Likely
More than 12 g total	Potentially fatal

If the patient has ingested less than 150 mg/kg paracetamol it is unlikely that serious toxicity will occur. If the patient has risk factors (see below) consider treatment at a lower dose (75 mg/kg).

Note NPIS advises that for very obese patients (> 110 kg) the toxic dose in mg/kg should be calculated using a maximum of 110 kg, rather than the patient's actual weight. Similarly the antidote dose should also be based on a maximum of 110 kg for this very obese group.

Paracetamol Index

Updated 1/2005

Paracetamol - staggered overdoses

Updated 6/2005

If the patient has ingested less than 150 mg/kg paracetamol in 24 hours it is unlikely that serious toxicity will occur. If the patient has risk factors (see below) consider treatment at a lower dose (75 mg/kg). Note that for obese patients (> 110 kg) the toxic dose in mg/kg should be calculated using 110 kg, rather than their actual weight.

All patients who have ingested more than 150 mg/kg in 24 hours should be considered for treatment with N-acetylcysteine.

Patients who may be at special risk include:
(a) those on long term treatment with carbamazepine, phenobarbitone, phenytoin, primidone, rifampicin or St John's Wort
(b) those who regularly consume ethanol in excess of recommended amounts
(c) those who are likely to be glutathione deplete e.g. eating disorders, cystic fibrosis

INR, plasma creatinine and ALT should be monitored. If these are normal 24 hours after the last ingestion significant toxicity is unlikely and N-acetylcysteine can be discontinued.

The plasma paracetamol concentration cannot be directly used on the nomogram but may confirm ingestion. Discuss with your local poisons service: in the UK NPIS 0870 600 6266, in Ireland NPIC (01) 809 2566.



Paracetamol Antidotes

Updated 7/2004

Intravenous therapy with N-acetylcysteine is recommended, particularly if vomiting is a problem or urgent treatment is required.

A previous anaphylactoid reaction to N-acetylcysteine is NOT an absolute contraindication for a further treatment course. If there has been a previous reaction NPIS advice is to pre-treat with an antihistamine (e.g. chlorphenamine 10 mg IV) and to ensure that the first bag of antidote is given no faster than the advised rate. Alternatively, local NPIS centres suggest that an initial infusion given over 1 hour (unlicensed) may be a successful strategy.

Methionine may be a suitable alternative for remote areas, if available, and if there will be delay in transfer to hospital.

Paracetamol - NAC doses

Updated 11/2005

WARNING!

1 Calculate the dose for each patient CAREFULLY and note that:

EACH MILLILITRE OF PARVOLEX CONTAINS 200 mg N-ACETYLCYSTEINE

EACH AMPOULE OF PARVOLEX CONTAINS 2 g N-ACETYLCYSTEINE

2 GET YOUR ARITHMETIC CHECKED BEFORE STARTING THE INFUSION

3. N-acetyl cysteine (Parvolex, NAC) is water soluble and the blood component of an obese patient will not be much different from an average weight patient. According to the manufacturers the maximum dosage of NAC is based on a 110 kg patient. It is therefore suggested that doses of NAC be calculated using a body weight of 110 kg for those patients who weigh more than 110 kg. Using higher doses of NAC may increase the risk of anaphylactoid reactions.

N-ACETYLCYSTEINE (PARVOLEX) DOSES FOR INTRAVENOUS INFUSION

ADULT (>12 YEARS)

Note NPIS advise that for very obese patients (> 110 kg) the antidote dose should be based on a maximum of 110 kg for this very obese group.

Give the following doses in sequence:

	PARVOLEX	Volume of 5% dextrose
Dose	mg/kg body weight	for dilution	Duration of infusion
1	150	200 mL	15 min
2	50	500 mL	4 hours
3	100	1000 mL	16 hours
If for any reason dextrose is unsuitable, 0.9% sodium chloride solution may be substituted.

CHILDREN < 12 YEARS AND 20 KG OR OVER

 

	PARVOLEX	Volume of 5% dextrose
Dose	mg/kg body weight	for dilution	Duration of infusion
1	150	100 mL	15 min
2	50	250 mL	4 hours
3	100	500 mL	16 hours
If for any reason dextrose is unsuitable, 0.9% sodium chloride solution may be substituted.

CHILDREN - BODY WEIGHT LESS THAN 20 KG

(From Alder Hey Book of Children's Doses, Sixth Edition 1996)

 

	PARVOLEX	Volume of 5% dextrose
Dose	(mg/kg body weight)	for dilution	Duration of infusion
1	150	3 mL/kg body weight	15 min
2	50	7 mL/kg body weight	4 hours
3	100	14 mL/kg body weight	16 hours
If for any reason dextrose is unsuitable, 0.9% sodium chloride solution may be substituted.

The patient should be medically fit for discharge when the course of antidote has been completed. If the treatment was started within 8 hours of ingesting the overdose the risk of liver or renal damage is insignificant. When the course of antidote has been completed check the INR, plasma creatinine, plasma bicarbonate and ALT. If they are normal the patient can be discharged with advice to return to hospital if vomiting or abdominal pain occur.

Treatment with N-acetylcysteine has been associated with mild elevation of the INR. Patients who have a marginally elevated INR (1.3 or less) but normal ALT do not require further monitoring or treatment with N-acetylcysteine. If both the INR and ALT are elevated, then continue giving N-acetylcysteine at a rate of 150 mg/kg over 24 hours. It is not necessary to give a further loading dose unless a second overdose has been taken.

If the plasma creatinine is raised continue to check renal function as an inpatient. Isolated renal failure is a rare, but well recognised complication. N-acetylcysteine has not been tested as an antidote for this complication and it should therefore not be continued to treat isolated renal impairment

Methionine