N-acetyl-L-cysteine
Meaning of N-acetyl-L-cysteine: The antidote that makes an acetaminophen overdose survivable, by refilling the liver's supply of a protective molecule the drug has burned through.
Definition of N-acetyl-L-cysteine
N-acetyl-L-cysteine is a modified form of the amino acid cysteine, used as a medicine in two quite different ways. Given into a vein or by mouth, it supplies the raw material for glutathione, the molecule the liver uses to neutralize the toxic breakdown product of acetaminophen. Inhaled or dripped into an airway, it breaks the chemical bonds that make mucus thick and stringy.
How does it work in an overdose?
Most of a normal dose of acetaminophen is joined to another molecule and passed out in urine. A small share takes a different route and becomes a highly reactive compound, which glutathione mops up before it can do harm. In overdose the ordinary routes saturate, far more of the reactive compound is made, and the glutathione reserve runs out. What is left attacks liver cells directly. This drug carries cysteine into the liver, and cysteine is the ingredient that limits how fast glutathione can be rebuilt. Its protective effect is greatest when it is started before injury takes hold, which is why the timing of treatment matters more than the size of the dose swallowed.
How does it thin mucus?
The strands of protein that give mucus its stringiness are stitched together by sulfur bridges. This molecule carries a free sulfur group that breaks those bridges apart, so the mesh loosens and the secretion becomes runnier and easier to clear. The effect is chemical and immediate, and it happens in a specimen pot as readily as in an airway.
How is it given, and what are the drawbacks?
| Route | Given for | Common problem |
|---|---|---|
| Into a vein | Acetaminophen overdose | Flushing, rash and wheeze during the infusion |
| By mouth | Overdose where infusion is unsuitable | A sulfurous smell, nausea and vomiting |
| Inhaled or instilled | Thick airway secretions | Can tighten the airways in asthma |
The reaction seen during an infusion looks alarming but is driven by the rate of delivery rather than by a true allergy, and it does not usually prevent the course from being completed. The same compound, also sold as acetylcysteine, is marketed as a supplement for a long list of unrelated claims that rest on far weaker evidence than its two established uses.
Also known as
Used in a sentence
N-acetyl-L-cysteine was started on presentation following the overdose.
Good to know
The reaction of flushing, rash and wheeze during an infusion is related to the rate of delivery rather than to true allergy, and the antidote effect depends heavily on how early treatment begins rather than on the amount swallowed.