Acetylcysteine

This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (March 2009)

Acetylcysteine
Systematic (IUPAC) name
(R)-2-acetamido-3-sulfanylpropanoic acid
Identifiers
CAS number	616-91-1
ATC code	R05CB01 S01XA08 V03AB23
PubChem	12035
DrugBank	n/a
ChemSpider	11540
Chemical data
Formula	C5H9NO3S
Mol. mass	163.19
SMILES	eMolecules & PubChem
Synonyms	(R)-2-acetamido-3-mercaptopropanoic acid
Pharmacokinetic data
Bioavailability	6–10% (oral) <3% (topical)
Metabolism	hepatic
Half life	5.6 hours (adults) 11 hours (neonates)
Excretion	renal
Therapeutic considerations
Licence data	US FDA:link
Pregnancy cat.	B2 (Aus)
Legal status	Schedule 4 (Aus) OTC or Rx (U.S.)
Routes	inhalation, IV, oral
Y(what is this?)  (verify)

Acetylcysteine (rINN; pronounced /ˌæsɨtəlˈsɪstiːn, əˌsɛtəlˈsɪstiːn/), also known as N-acetylcysteine or N-acetyl-L-cysteine (abbreviated NAC), is a pharmaceutical drug used mainly as a mucolytic agent and in the management of paracetamol (acetaminophen) overdose.

Trade names

Acetylcysteine is marketed under these trade names:

• ACC (Hexal AG)
• Acetadote (Cumberland Pharmaceuticals)
• Asist (Bilim Pharmaceuticals)
• Lysox (Menarini)
• Mucinac (Cipla, India)
• Mucolysin (Sandoz)
• Mucomelt-A tab (Venus Remedies, India)
• Mucomyst (Bristol-Myers Squibb)
• Parvolex (GSK)
• Trebon N (Uni-pharma).
• Fluimucil (Zambon).
• Flumil (Pharmazam, Spain).
• Rheunac (Tree Of Life, Israel).

Dosage forms

Acetylcysteine is available in different dosage forms for different indications:

• Solution for inhalation (Asist,Mucomyst, Mucosil) – inhaled for mucolytic therapy or ingested for nephroprotective effect (to protect the kidneys)
• IV injection (Asist,Parvolex, Acetadote) – treatment of paracetamol/acetaminophen overdose
• Oral solution – various indications.
• Effervescent Tablets (200 mg) - Reolin (Hochland Pharma Germany), Solmucol (600mg)(IBSA, Switzerland) and Mucinac (Cipla India).
• Ocular solution - for mucolytic therapy
• Sachet (600 mg) - Bilim Pharmaceuticals

The IV injection and inhalation preparations are, in general, prescription only, whereas the oral solution and the effervescent tablets are available over the counter in many countries.

Clinical use

Mucolytic therapy

Inhaled acetylcysteine is indicated for mucolytic ("mucus-dissolving") therapy as an adjuvant in respiratory conditions with excessive and/or thick mucus production. Such conditions include emphysema, bronchitis, tuberculosis, bronchiectasis, amyloidosis, pneumonia. It is also used post-operatively, as a diagnostic aid, and in tracheotomy care. It may be considered ineffective in cystic fibrosis.^[1] However, a recent paper in the Proceedings of the National Academy of Sciences reports that high-dose oral N-acetylcysteine modulates inflammation in cystic fibrosis and has the potential to counter the intertwined redox and inflammatory imbalances in CF.^[2] Oral acetylcysteine may also be used as a mucolytic in less serious cases.

For this indication, acetylcysteine acts to reduce mucus viscosity by splitting disulfide bonds linking proteins present in the mucus (mucoproteins).

Paracetamol (Acetaminophen) overdose

Intravenous acetylcysteine is indicated for the treatment of paracetamol (acetaminophen) overdose. When paracetamol is taken in large quantities, a minor metabolite called N-acetyl-p-benzoquinone imine (NAPQI) accumulates within the body. It is normally conjugated by glutathione, but when taken in excess, the body's glutathione reserves are not sufficient to inactivate the toxic NAPQI. This metabolite is then free to react with key hepatic enzymes, therefore damaging hepatocytes. This may lead to severe liver damage and even death by fulminant liver failure.

For this indication, acetylcysteine acts to augment the glutathione reserves in the body and, together with glutathione, directly bind to toxic metabolites. These actions serve to protect hepatocytes in the liver from NAPQI toxicity.

Although both IV and oral acetylcysteine are equally effective for this indication, oral administration is poorly tolerated, owing to the high doses required (due to low oral bioavailability,^[3]) very unpleasant taste and odour, and adverse effects (particularly nausea and vomiting). Studies conducted by Baker and Dilger^[4] suggest that the prior pharmacokinetic studies of N-acetylcysteine did not include Acetylation as a reason for the low bioavailability of N-acetylcysteine. In the research conducted by Baker,^[4] it was concluded that oral N-acetylcysteine was identical in bioavailability to Cysteine precursors. (However, 3% to 6% of people given intravenous acetylcysteine show a severe, anaphylaxis-like allergic reaction, which may include extreme breathing difficulty (due to bronchospasm), a decrease in blood pressure, rash, angioedema, and sometimes also nausea and vomiting. ^[5] Repeated overdoses will cause the allergic reaction to progressively worsen.)

Several studies have found this anaphylaxis-like reaction to occur more often in people given IV acetylcysteine despite serum levels of paracetamol not high enough to be considered toxic. ^[6][7][8][9]

In some countries, a specific intravenous formulation does not exist to treat paracetamol overdose. In these cases, the formulation used for inhalation may be used intravenously.

Nephroprotective agent

Oral acetylcysteine is used for the prevention of radiocontrast-induced nephropathy (a form of acute renal failure). Some studies show that prior administration of acetylcysteine markedly decreases (90%) radiocontrast nephropathy,^[10] whereas others appear to cast doubt on its efficacy.^[11][12] Worth considering is the newest data published in two papers in the New England Journal of Medicine and the Journal of the American Medical Association. The authors' conclusions in those papers were:

1. "Intravenous and oral N-acetylcysteine may prevent contrast-medium–induced nephropathy with a dose-dependent effect in patients treated with primary angioplasty and may improve hospital outcome."^[13]
2. "Acetylcysteine protects patients with moderate chronic renal insufficiency from contrast-induced deterioration in renal function after coronary angiographic procedures, with minimal adverse effects and at a low cost"^[14]

Acetylcysteine continues to be commonly used in individuals with renal impairment to prevent the precipitation of acute renal failure.^{[citation needed]}

Microbiological use

N-Acetyl L-Cysteine can be used in Petroff's method i.e. liquefaction and decontamination of sputum, in preparation for diagnosis of tuberculosis.

Interstitial lung disease

Acetylcysteine is used in the treatment of interstitial lung disease to prevent disease progression.^{[citation needed]}

Investigational

The following uses have not been well-established or investigated:

• NAC has been shown to reduce the symptoms of both schizophrenia^[15] and bipolar disorder^[16] in two placebo controlled trials.
• Evidence that NAC and other antioxidants can exert beneficial effects on pancreatic b-cell function in diabetes was published in a 1999 study. The authors conclude that a sufficient supply of antioxidants (NAC, vitamin C plus vitamin E, or both) may prevent or delay b-cell dysfunction in diabetes by providing protection against glucose toxicity.^[17]

• NAC is undergoing clinical trials in the United States for the treatment of obsessive-compulsive disorder.^[18] It is thought to counteract the glutamate hyperactivity in OCD.
• NAC has been shown to reduce cravings associated with chronic cocaine use in a study conducted at the Medical University of South Carolina^[19][20]
• It may reduce the incidence of chronic obstructive pulmonary disease (COPD) exacerbations^[21]
• In the treatment of AIDS, NAC has been shown to cause a "marked increase in immunological functions and plasma albumin concentrations"^[22] Albumin concentration are inversely correlated with muscle wasting (cachexia), a condition associated with AIDS.
• An animal study indicates that acetylcysteine may decrease mortality associated with influenza ^[23]
• Animal studies suggest that NAC may help prevent noise-induced hearing loss. ^[24] A clinical trial to determine efficacy in preventing noise-induced sensorineural hearing loss in humans is currently (2006) being jointly conducted by the US Army and US Navy.^{[citation needed]}
• A human study of 262 primarily elderly individuals indicates that NAC may decrease influenza symptoms. In the study, 25% of virus-infected subjects NAC treatment developed a symptoms, whereas 79% in the placebo group developed symptoms. ^[25]
• It has been suggested that NAC may help sufferers of Samter's triad by increasing levels of glutathione allowing faster breakdown of salicylates, though there is no evidence that it is of benefit ^[26]
• There are claims that acetylcysteine taken together with vitamin C and B1 can be used to prevent and relieve symptoms of veisalgia (hangover following ethanol (alcohol) consumption). The claimed mechanism is through scavenging of acetaldehyde, a toxic intermediate in the metabolism of ethanol.^[27][28]
• It has been shown to help women with PCOS (polycystic ovary syndrome) to reduce insulin problems and possibly improve fertility. ^[29]
• Small studies have shown acetylcysteine to be of benefit to sufferers of blepharitis^{[citation needed]} and has been shown to reduce ocular soreness caused by Sjogren's syndrome.^{[citation needed]}
• Studies in mice models of Ataxia Telangictasia (ATM knockout) indicate that NAC prevents genomic instability and retards lymphomagenesis in these animals.^{[citation needed]} Clinical trials in human AT patients are underway.^{[citation needed]}
• It has been shown to help trichotillomania^[30], a condition causing compulsive hair-pulling.
• It has been shown to help methylmercury poisoning^[31]
• It has been shown effective in Unverricht-Lundborg disease in an open trial in 4 patients. A marked decrease in myoclonus and some normalization of somatosensory evoked potentials with N -acetylcysteine treatment has been documented. http://emedicine.medscape.com/article/1153370-overview

Complexing agent

N-Acetylcysteine has been used to complex palladium, to help it dissolve in water. This helps to remove palladium from drugs or precursors synthesized by palladium-coupling reactions.^[32]

Chemistry

Acetylcysteine is the N-acetyl derivative of the amino acid L-cysteine, and is a precursor in the formation of the antioxidant glutathione in the body. The thiol (sulfhydryl) group confers antioxidant effects and is able to reduce free radicals.

Possible toxicity

Researchers at the University of Virginia reported in 2007 study using very large doses in a mouse model that acetylcysteine, which is found in many bodybuilding supplements, could potentially cause damage to the heart and lungs.^[33] They found that acetylcysteine was metabolized to S-nitroso-N-acetylcysteine (SNOAC), which increased blood pressure in the lungs and right ventricle of the heart (pulmonary artery hypertension) in mice treated with acetylcysteine. The effect was similar to that observed following a 3-week exposure to an oxygen-deprived environment (chronic hypoxia). The authors also found that SNOAC induced a hypoxia-like response in the expression of several important genes both in vitro and in vivo.

The implications of these findings for long-term treatment with acetylcysteine have not yet been investigated. The dose used by Palmer and colleagues was dramatically higher than that used in humans;^[33] nonetheless, the drug's effects on the hypoxic ventilatory response have been observed previously in human subjects at more moderate doses.^[34]

See also

• Glutathione
• Cysteine

References

• CIMS India database "[1]"

References

• British National Formulary 55, March 2008; ISBN 978 085369 776 3