Acetylcysteine (N-acetylcysteine — Paracetamol Overdose)

Source: eMC SPC for Acetylcysteine 200mg/ml Injection (each ampoule = 200 mg/mL). Dosage should be calculated using the patient's actual weight, subject to the 110 kg ceiling in obese patients. Continued treatment with acetylcysteine, given at the dose and rate used in the third infusion, may be necessary depending on the clinical evaluation of the individual patient. Timing (SPC §4.4): indicated within 24 hours of ingestion of a potentially hepatotoxic paracetamol overdose; most effective when given within 8 to 10 hours; efficacy diminishes between 10 and 24 hours but it should still be given up to 24 hours, and may still be administered after 24 hours in patients at risk of severe liver damage. Anaphylactoid reactions occur particularly with the initial loading dose — observe the patient carefully during this period; most can be managed by temporarily suspending the infusion, giving supportive care and restarting at a lower infusion rate, normally 50 mg/kg over 4 hours followed by the final 100 mg/kg over 16 hours. Use with caution in children, patients requiring fluid restriction and those weighing less than 40 kg because of the risk of fluid overload, which may cause hyponatraemia and life-threatening seizures. Each 10 mL of the injection contains 322.6 mg sodium. Monitoring of plasma potassium is recommended — hypokalaemia and ECG changes occur in paracetamol poisoning irrespective of the treatment given. An isolated rise in prothrombin time up to 1.3 at the end of a 21-hour course without elevated transaminase activity does not require further monitoring or treatment.

SPC §4.2: 'Children should be treated with the same doses and regimen as adults; however, the quantity of intravenous fluid used should be modified to take into account age and weight, as fluid overload is a potential danger.' Dose 1 — 150 mg/kg over 1 hour (150 mg/kg/h), given as a 50 mg/mL solution at 3 mL/kg/h. Dose 2 — 50 mg/kg over 4 hours (12.5 mg/kg/h), given as a 6.25 mg/mL solution at 2 mL/kg/h. Dose 3 — 100 mg/kg over 16 hours (6.25 mg/kg/h), given as a 6.25 mg/mL solution at 1 mL/kg/h. Preparation: Dose 1 — dilute each 10 mL ampoule (200 mg/mL) with 30 mL glucose 5% or sodium chloride 0.9% to a total volume of 40 mL; Doses 2 and 3 — dilute each 10 mL ampoule with 310 mL to a total volume of 320 mL. Caution: risk of fluid overload, hyponatraemia and seizures in children and in patients weighing less than 40 kg. Verify against a children's formulary.