What Acetylcysteine Injection is and what it is used for.

Acetylcysteine Injection is used for the treatment of paracetamol overdose (where you may have taken too much paracetamol). You will be given Acetylcysteine Injection if you have taken a potentially harmful amount of paracetamol. Acetylcysteine protects the liver from damage by the high levels of paracetamol. It is very effective when given during the first 8 hours following paracetamol overdose. The effectiveness is reduced as the time interval increases, but it can still help when given up to 24 hours after the overdose.

What you need to know before you take Acetylcysteine Injection.

The level of paracetamol in your blood should be checked before treatment is started.

Warnings and precautions

Talk to your doctor or nurse before using Acetylcysteine Injection if:

  • you suffer from asthma or breathing difficulties
  • you have had an adverse reaction to Acetylcysteine before
  • you are pregnant or breast-feeding

If you have any doubts about whether this medicine should be given to you, discuss things more fully with the doctor or nurse.

Other medicines and Acetylcysteine Injection

Tell your doctor if you are taking, have recently taken or might take any other medicines.

Pregnancy, breast-feeding and fertility

If you are pregnant or breast-feeding, think you may be pregnant or planning to have a baby, ask your doctor or nurse for advice before being given this medicine.

 Driving and using machines

It is unlikely that after using Acetylcysteine Injection, your ability to drive and use machines will be affected. However, if you feel unwell you must speak to your doctor before driving or operating machinery.

How to take Acetylcysteine Injection

Acetylcysteine Injection will be diluted in glucose or sodium chloride solution and given as an intravenous infusion (a drip into a vein) by a doctor or nurse.


Acetylcysteine Injection is given in three stages. During each stage a different dose of Acetylcysteine will be given. You will be given a total dose of 300mg of Acetylcysteine per kg of your body weight, over a period of 21 hours. Some patients may require longer treatment with acetylcysteine. The doctor will calculate how much to give you in each stage.


Children should be given Acetylcysteine Injection in three stages, like adults. However, the amount of fluid used to dilute Acetylcysteine Injection will be calculated to take into consideration the age and weight of the child, as too much fluid can be harmful. Blood tests may be carried out before, during and after treatment with this medicine.

Possible side effects

Tell your doctor or nurse immediately if you notice any of the following:

  • swelling of the face, lips or tongue
  • wheezing, difficulty in breathing
  • feeling or being sick
  • irritation at the injection site
  • skin rash, itching
  • flushing (red face or feeling hot)
  • low blood pressure resulting in dizziness
  • rapid heartbeat or increased blood pressure. 

 These symptoms often happen 15 to 60 minutes after the start of the infusion, and may be relieved by stopping the infusion. You may need to be treated with antihistamines or corticosteroids. Once the reaction is under control the infusion can be restarted.

Therapeutic indications

N-acetylcysteine is indicated for the treatment of paracetamol overdose in patients:

  • who have taken a staggered overdose irrespective of plasma paracetamol level. Staggered is defined as an overdose where the paracetamol was ingested over a period of 1 hour or more; or
  • where there is any doubt over the time of the overdose, irrespective of plasma paracetamol level; or
  • who present with a plasma paracetamol level on or above a line joining points of 100mg/L at 4h and 15mg/L at 15h (see below nomogram).

Method of administration

The injection should be administered by intravenous infusion preferably using Glucose 5% as the infusion fluid. Sodium Chloride 0.9% solution may be used if Glucose 5% is not suitable.


There are no contraindications to the treatment of paracetamol overdose with N-acetylcysteine.

Special warnings and precautions for use

Intravenous N-acetylcysteine, given within 24 hours of ingestion of a potentially hepatotoxic overdose of paracetamol, is indicated to prevent or reduce the severity of liver damage. It is most effective when administered within 8 to 10 hours of a paracetamol overdose. Although the efficacy of N-acetylcysteine diminishes between 10 and 24 hours post-overdose, it should be administered up to 24 hours as it can still be of benefit. It may still be administered after 24 hours in patients at risk of severe liver damage.

Anaphylactoid reactions

Anaphylactoid hypersensitivity reactions occur with N-acetylcysteine, particularly with the initial loading dose. The patient should be carefully observed during this period for signs of an anaphylactoid reaction. Nausea, vomiting, flushing, skin rash, pruritus and urticaria are the most common features, but more serious anaphylactoid reactions have been reported where the patient develops angioedema, bronchospasm, respiratory distress, tachycardia and hypotension. In very rare cases these reactions have been fatal. There is some evidence that patients with a history of atopy and asthma may be at increased risk of developing an anaphylactoid reaction.

Most anaphylactoid reactions can be managed by temporarily suspending the N-acetylcysteine infusion, administering appropriate supportive care and restarting at a lower infusion rate. Once an anaphylactoid reaction is under control, the infusion can normally be restarted at an infusion rate of 50 mg/kg over 4 hours, followed by the final 16 hour infusion (100 mg/kg over 16 hours).


Changes in haemostatic parameters have been observed in association with N-acetylcysteine treatment, some leading to decreased prothrombin time, but most leading to a small increase in prothrombin time. An isolated increase in prothombin time up to 1.3 at the end of a 21 hour course of N-acetylcysteine without an elevated transaminase activity do not require further monitoring or treatment with N-acetylcysteine.

Fluid and electrolytes

Use with caution in children, patients requiring fluid restriction or those who weigh less than <40 kg because of the risk of fluid overload which may result in hyponatraemia and seizures which may be life threatening.

Each 10ml of N-acetylcysteine for Infusion contains 322.6mg sodium. To be taken into consideration with patients on a controlled sodium diet.

Possible side effects

The most common adverse reactions reported with N-acetylcysteine are nausea, vomiting, flushing and skin rash.

Less commonly, more serious anaphylactoid reactions have been reported that include angioedema, bronchospasm/respiratory distress, hypotension, tachycardia or hypertension.

Adverse reactions to N-acetylcysteine usually occur between 15 and 60 minutes after the start of infusion and, in many cases, symptoms are relieved by stopping the infusion. An antihistamine drug may be necessary, and occasionally corticosteroids may be required. Once an adverse reaction is under control, the infusion can normally be restarted at the lowest infusion rate (100mg/kg in 1 litre over 16 hours).

Other reported adverse reactions include: injection site reactions, pruritus, cough, chest tightness or pain, puffy eyes, sweating, malaise, raised temperature, vasodilation, blurred vision, bradycardia, facial or eye pain, syncope, acidosis, thrombocytopenia, respiratory or cardiac arrest, stridor, anxiety, extravasation, arthropathy, arthralgia, deterioration of liver function, generalised seizure, cyanosis, lowered blood urea.

Case reports of fatalities with N-acetylcysteine have been reported very rarely.

Hypokalaemia and ECG changes have been noted in patients with paracetamol poisoning irrespective of the treatment given. Monitoring of plasma potassium concentration is, therefore, recommended.

If any adverse reactions to N-acetylcysteine develop, advice should be sought from the National Poisons Centre to ensure that the patient receives adequate treatment of the paracetamol overdose.

Reporting of suspected adverse reactions

Reporting suspected adverse reactions after authorisation of the medicinal product is important. It allows continued monitoring of the benefit/risk balance of the medicinal product.