Acetylcysteine (also known as N-acetylcysteine or N-acetyl-L-cysteine or NAC) is primarily used as a mucolytic agent and in the management of acetaminophen poisoning. It is a derivative of cysteine with an acetyl group attached to the amino group of cysteine.
NAC is essentially a prodrug that is converted to cysteine (in the intestine by the enzyme aminoacylase 1) and absorbed in the intestine into the blood stream. Cysteine is a key constituent to glutathione and hence administration of acetylcysteine replenishes glutathione stores.
N-acetylcysteine is now widely used in the treatment of HIV, and it has reported efficacy in chronic obstructive pulmonary disease and contrast-induced nephropathy. Acetylcysteine is also being successfully used to treat a variety of neuropsychiatric and neurodegenerative disorders including cocaine, cannabis, and smoking addictions, Alzheimer’s and Parkinson’s diseases, autism, compulsive and grooming disorders, schizophrenia, depression, and bipolar disorder.
When inhaled by mouth, acetylcysteine is used to help thin and loosen mucus in the airways due to certain lung diseases (such as emphysema, bronchitis, cystic fibrosis, pneumonia). This effect helps you to clear the mucus from your lungs so that you can breathe easier.
When taken by mouth, acetylcysteine is used to prevent liver damage from acetaminophen overdose.
Mechanism of action
Acetylcysteine protects against acetaminophen overdose-induced hepatotoxicity by maintaining or restoring hepatic concentrations of glutathione. It does this by producing the glutathione precursor L-cysteine. Glutathione is required to inactivate an intermediate metabolite (N-acetyl-p-benzoquinoneimine or NAPQI) of acetaminophen that is thought to be hepatotoxic.
In acetaminophen overdose cases, excessive quantities of this metabolite are formed because the primary metabolic (glucuronide and sulfate conjugation) pathways become saturated. Acetylcysteine may act by reducing the metabolite to the parent compound and/or by providing sulfhydryl for conjugation of the metabolite. Experimental evidence also suggests that a sulfhydryl-containing compound such as acetylcysteine may also directly inactivate the metabolite.
The mechanisms of action for acetylcysteine’s well-known mucolytic effects are different. In particular, when inhaled, acetylcysteine (and its metabolic byproduct cysteine) exerts its mucolytic action through its free sulfhydryl group, which reduces the disulfide bonds in the mucus matrix and lowers mucus viscosity. This action increases with increasing pH and is most significant at pH 7 to 9. The mucolytic action of acetylcysteine is not affected by the presence of DNA.
Acetylcysteine is also an antioxidant and reduces oxidative stress. Acetylcysteine serves as a prodrug to L-cysteine which is a precursor to the biologic antioxidant, glutathione and hence administration of acetylcysteine replenishes glutathione stores. L-cysteine also serves as a precursor to cystine which in turn serves as a substrate for the cystine-glutamate antiporter on astrocytes hence increasing glutamate release into the extracellular space. This glutamate in turn acts on mGluR2/3 receptors, and at higher doses of acetylcysteine, mGluR5. Glutathione also modulates the NMDA receptor by acting at the redox site.
These effects on glutamate and NMDA signaling appear to explain some of the positive neuropsychotropic effects associated with NAC. Acetylcysteine also possesses some anti-inflammatory effects possibly via inhibiting NF-κB through redox activation of the nuclear factor kappa kinases thereby modulating cytokine synthesis
Acetylcysteine Side Effects
Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.
Stop using acetylcysteine inhalation and call your doctor at once if you have: chest tightness; or trouble breathing.
Common side effects may include:
- sticky feeling around the nebulizer mask;
- white patches or sores inside your mouth or on your lips;
- nausea, vomiting;
- fever, runny nose, sore throat;
- drowsiness; or
- Cold and clammy skin.
This is not a complete list of side effects and others may occur
Before using acetylcysteine, tell your doctor or pharmacist if you are allergic to it; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.
Before using this medication, tell your doctor or pharmacist your medical history, especially of: asthma, stomach/intestinal ulcer.
During pregnancy, this medication should be used only when clearly needed. Discuss the risks and benefits with your doctor.
It is unknown if this drug passes into breast milk. Consult your doctor before breast-feeding.
The excretion of Atorvastatin can be decreased when combined with Acetylcysteine.
The excretion of Benzylpenicillin can be decreased when combined with Acetylcysteine.
The excretion of Bosentan can be decreased when combined with Acetylcysteine.
The excretion of Cerivastatin can be decreased when combined with Acetylcysteine.