acetylcysteine
Meaning of acetylcysteine: One molecule with two unrelated jobs: thinning sticky mucus in the airway, and rescuing the liver after a paracetamol overdose.
Definition of acetylcysteine
Acetylcysteine is a medicine used to thin thick mucus and to treat poisoning by acetaminophen. Inhaled or instilled into the airway, it breaks the chemical bridges that make mucus stiff, so it can be cleared. Given by mouth or by vein after an overdose, it restores the liver supply of glutathione, the molecule that neutralizes the toxic breakdown product of acetaminophen.
How does it thin mucus?
Thick mucus owes its stiffness to long protein chains linked to one another by sulfur bridges, in the way rungs hold a ladder together. Acetylcysteine carries a free sulfur group that attacks those bridges and breaks them, so the network falls apart and the fluid becomes runnier. The effect is chemical and immediate. Its sulfur content also gives the preparation a distinct smell of rotten eggs, which is a frequent complaint about the oral form.
How does it work in acetaminophen poisoning?
| Stage | What happens |
|---|---|
| Normal doses | Most of the drug is inactivated by safe routes |
| A small share | Becomes a reactive toxic compound |
| Glutathione | Neutralizes that compound harmlessly |
| Overdose | Glutathione runs out and the compound attacks liver cells |
| Acetylcysteine | Supplies the raw material to rebuild glutathione |
Its effectiveness falls the longer it is delayed, because the aim is to intercept the toxic compound before it binds to liver proteins. This is why acetaminophen overdose is treated on the basis of the amount taken and the time elapsed rather than waiting for liver damage to appear.
What else should be known about it?
Given by vein it can cause a reaction resembling an allergy, with flushing, rash, wheeze and a fall in blood pressure. It is caused by direct release of histamine rather than by a true allergic mechanism, so it does not necessarily prevent future use. Inhaled forms can trigger airway tightening in people with asthma. The names N-acetylcysteine and N-acetyl-L-cysteine refer to the same substance, which is also sold as a dietary supplement, a form not held to the same manufacturing standards as the medicine.
Also known as
Used in a sentence
Acetylcysteine was started by infusion following the reported overdose.
Good to know
In acetaminophen poisoning the benefit of acetylcysteine declines as time passes, because it works by replenishing glutathione before liver damage occurs rather than by reversing it afterward.