Acetylcysteine

How it works

It replenishes hepatic glutathione stores (and provides cysteine), allowing detoxification of the reactive paracetamol metabolite NAPQI before it binds to and damages hepatocytes, thereby preventing or limiting paracetamol-induced hepatic necrosis.

Prescribing in practice

• Treatment should be started promptly in significant paracetamol overdose, guided by the paracetamol nomogram and timing of ingestion, as efficacy is greatest when given early and benefit falls with delay.
• Anaphylactoid reactions (flushing, rash, bronchospasm, hypotension) can occur, particularly during the initial infusion, and are managed by slowing or pausing the infusion and giving supportive treatment rather than necessarily abandoning the antidote.
• Use with caution in patients with asthma given the risk of bronchospasm, and follow the current MHRA/UK guidance on infusion regimens and continuation criteria.

Monitoring

Monitor liver function tests, INR, renal function and the paracetamol concentration, with continuation of treatment guided by these results and the clinical course.

Counselling the patient

• Explain that this is the antidote that protects the liver after a paracetamol overdose and works best when given early.
• Warn that flushing or a rash during the infusion can occur and is managed by adjusting the infusion rate.
• Encourage engagement with psychosocial assessment and follow-up after the overdose.

Evidence & guidelines

Intravenous acetylcysteine is the established standard-of-care antidote for paracetamol poisoning in UK practice, with use directed by the paracetamol treatment nomogram and national poisons guidance.