Acetylcysteine, also known as N-acetylcysteine (NAC), is a medication that is used to treat paracetamol (acetaminophen) overdose, and to loosen thick mucus in individuals with cystic fibrosis or chronic obstructive pulmonary disease. It can be taken intravenously, by mouth, or inhaled as a mist. Some people use it as a dietary supplement.
Common side effects include nausea and vomiting when taken by mouth. The skin may occasionally become red and itchy with either form. A non-immune type of anaphylaxis may also occur. It appears to be safe in pregnancy. For paracetamol overdose, it works by increasing the level of glutathione, an antioxidant that can neutralise the toxic breakdown products of paracetamol. When inhaled, it acts as a mucolytic by decreasing the thickness of mucus.
Acetylcysteine was initially patented in 1960 and licensed for use in 1968. It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system. It is available as a generic medication and is not very expensive.
Video Acetylcysteine
Uses
Paracetamol overdose
Intravenous and oral formulations of acetylcysteine are available 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, thereby damaging liver cells. This may lead to severe liver damage and even death by acute liver failure.
In the treatment of acetaminophen overdose, acetylcysteine acts to maintain or replenish depleted glutathione reserves in the liver and enhance non-toxic metabolism of acetaminophen. These actions serve to protect liver cells from NAPQI toxicity. It is most effective in preventing or lessening hepatic injury when administered within 8-10 hours after overdose. Research suggests that the rate of liver toxicity is approximately 3% when acetylcysteine is administered within 10 hours of overdose.
Although both IV and oral acetylcysteine are equally effective for this indication, oral administration is poorly tolerated because high oral doses are required due to low oral bioavailability, because of its very unpleasant taste and odour, and because of adverse effects, particularly nausea and vomiting. Prior pharmacokinetic studies of acetylcysteine did not consider acetylation as a reason for the low bioavailability of acetylcysteine. Oral acetylcysteine is 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. Repeated doses of intravenous acetylcysteine will cause these allergic reactions to progressively worsen in these people.
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.
Mucolytic therapy
Inhaled acetylcysteine has been used for mucolytic ("mucus-dissolving") therapy in addition to other therapies in respiratory conditions with excessive and/or thick mucus production. It is also used post-operatively, as a diagnostic aid, and in tracheotomy care. It may be considered ineffective in cystic fibrosis. A 2013 Cochrane review in cystic fibrosis found no evidence of benefit.
Kidney disease
Some reviews found that prior administration of acetylcysteine decreases radiocontrast induced kidney disease, whereas another found questionable effects.
Despite the conflicting research outcomes, the 2012 Kidney Disease: Improving Global Outcomes Guidelines suggest the use of oral acetylcysteine for the prevention of contrast-induced nephropathy in high-risk individuals, given its potential for benefit, low likelihood of adverse effects, and low cost.
Haemorrhagic cystitis
Acetylcysteine has been used for cyclophosphamide-induced haemorrhagic cystitis, although mesna is generally preferred due to the ability of acetylcysteine to diminish the effectiveness of cyclophosphamide.
Obstructive lung disease
Acetylcysteine is used in the treatment of obstructive lung disease as an adjuvant treatment.
Psychiatry
Acetylcysteine has been successfully tried as a treatment for a number of psychiatric disorders. A systematic review from 2015, and several earlier medical reviews, indicated that there is favorable evidence for N-acetylcysteine efficacy in the treatment of Alzheimer's disease, bipolar disorder, major depressive disorder, obsessive-compulsive disorder, schizophrenia, specific drug addictions (cocaine), and a certain form of epilepsy (progressive myoclonic). Tentative evidence also supports use in cannabis use disorder.
Evidence to date does not support the efficacy for N-acetylcysteine in treating addictions to gambling, methamphetamine, or nicotine, although pilot controlled data are encouraging. Based upon preclinical evidence and limited clinical evidence, NAC appears to normalize glutamate neurotransmission into the nucleus accumbens and other brain structures, in part by upregulating the expression of excitatory amino acid transporter 2 (EAAT2), a.k.a. glutamate transporter 1 (GLT1), in individuals with addiction. While NAC has been demonstrated to modulate glutamate neurotransmission in adult humans who are addicted to cocaine, NAC does not appear to modulate glutamate neurotransmission in healthy adult humans.
NAC has been hypothesized to exert beneficial effects through its modulation of glutamate and dopamine neurotransmission as well as its antioxidant properties.
Microbiological use
Acetylcysteine can be used in Petroff's method i.e. liquefaction and decontamination of sputum, in preparation for recovery of mycobacterium. It also displays significant antiviral activity against the influenza A viruses.
Acetylcysteine has bactericidal properties and breaks down bacterial biofilms of clinically relevant pathogens including Pseudomonas aeruginosa, Staphylococcus aureus, Enterococcus faecalis, Enterobacter cloacae, Staphylococcus epidermidis, and Klebsiella pneumoniae.
Other uses
Acetylcysteine is commonly sold as a dietary supplement for antioxidant and purported liver protecting effects.
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-catalyzed coupling reactions.
Maps Acetylcysteine
Side effects
The most commonly reported adverse effects for IV formulations of acetylcysteine are rash, urticaria, and itchiness. Up to 18% of patients have been reported to experience anaphylaxis reaction, which are defined as rash, hypotension, wheezing, and/or shortness of breath. Lower rates of anaphylactoid reactions have been reported with slower rates of infusion.
Adverse effects for inhalational formulations of acetylcysteine include nausea, vomiting, stomatitis, fever, rhinorrhea, drowsiness, clamminess, chest tightness, and bronchoconstriction. Although infrequent, bronchospasm has been reported to occur unpredictably in some patients.
Adverse effects for oral formulations of acetylcysteine have been reported to include nausea, vomiting, rash, and fever.
Large doses in a mouse model showed that acetylcysteine could potentially cause damage to the heart and lungs. 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, the equivalent of about 20 grams per day. Nonetheless, positive effects on age-diminished control of respiration (the hypoxic ventilatory response) have been observed previously in human subjects at more moderate doses.
Although N-acetylcysteine prevented liver damage when taken before alcohol, when taken four hours after alcohol it made liver damage worse in a dose-dependent fashion.
Pharmacology
Pharmacodynamics
Acetylcysteine serves as a prodrug to L-cysteine.
L-cysteine is a precursor to the biologic antioxidant glutathione. Hence administration of acetylcysteine replenishes glutathione stores.
- Glutathione, along with oxidized glutathione (GSSG) and S-nitrosoglutathione (GSNO), have been found to bind to the glutamate recognition site of the NMDA and AMPA receptors (via their ?-glutamyl moieties), and may be endogenous neuromodulators. At millimolar concentrations, they may also modulate the redox state of the NMDA receptor complex. In addition, glutathione has been found to bind to and activate ionotropic receptors that are different from any other excitatory amino acid receptor, and which may constitute glutathione receptors, potentially making it a neurotransmitter. As such, since N-acetylcysteine is a prodrug of glutathione, it may modulate all of the aforementioned receptors as well.
- Glutathione also modulates the NMDA receptor by acting at the redox site.
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.
Acetylcysteine also possesses some anti-inflammatory effects possibly via inhibiting NF-?B and modulating cytokine synthesis.
Pharmacokinetics
Acetylcysteine is extensively liver metabolized, CYP450 minimal, urine excretion is 22-30% with a half-life of 5.6 hours in adults and 11 hours in neonates.
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.
N-acetyl-L-cysteine is soluble in water and alcohol, and practically insoluble in chloroform and ether.
It is a white to white with light yellow cast powder, and has a pKa of 9.5 at 30 °C.
Dosage forms
Acetylcysteine is available in different dosage forms for different indications:
- Solution for inhalation (Assist, Mucomyst, Mucosil) - inhaled for mucolytic therapy or ingested for nephroprotective effect (kidney protection)
- Intravenous injection (Assist, Parvolex, Acetadote) - treatment of paracetamol/acetaminophen overdose
- Oral solution - various indications.
- Effervescent tablets
- Ocular solution - for mucolytic therapy
- Tablets - sometimes in a sustained release formula sold as a nutritional supplement
- Capsules
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. Acetylcysteine is available as a health supplement in the United States, typically in capsule form.
Research
While many antioxidants have been researched to treat a large number of diseases by reducing the negative effect of oxidative stress, acetylcysteine is one of the few that has yielded promising results, and is currently already approved for the treatment of paracetamol overdose.
- In mouse mdx models of Duchenne's muscular dystrophy, treatment with 1-2% acetylcysteine in drinking water significantly reduces muscle damage and improves strength.
- It is being studied in conditions, such as autism, where cysteine and related sulfur amino acids may be depleted due to multifactorial dysfunction of methylation pathways involved in methionine catabolism.
- Acetylcysteine in a double-blind placebo-controlled trial appears to reduce the effects of blast induced mild traumatic brain and neurological injury in soldiers. Animal studies have also demonstrated its efficacy in reducing the damage associated with moderate traumatic brain or spinal injury, and also ischaemia-induced brain injury. In particular, it has been demonstrated to reduce neuronal losses and to improve cognitive and neurological outcomes associated with these traumatic events.
- It has been suggested that acetylcysteine may help people with Samter's triad by increasing levels of glutathione allowing faster breakdown of salicylates, although there is no evidence that it is of benefit.
- It has been shown to help women with PCOS (polycystic ovary syndrome) to reduce insulin problems and possibly improve fertility.
- Small studies have shown acetylcysteine to be of benefit to people with blepharitis. and has been shown to reduce ocular soreness caused by Sjögren's syndrome.
- It has been shown effective in the treatment of Unverricht-Lundborg disease in an open trial in four patients. A marked decrease in myoclonus and some normalization of somatosensory evoked potentials with acetylcysteine treatment has been documented.
- The effect of acetylcysteine in combination with glucocorticoids (combination group) for people who have severe alcoholic hepatitis was examined and showed that the combination of acetylcysteine with prednisolone decreased mortality significantly at one month compared to the prednisolone-only group (8% vs 24%, P=0.006). However, the improvement was not as significant at 3 months or 6 months (22% vs 34%, P=0.06) and (27% vs 38%, P=0.07). Factors that were associated with increased 6-month survival included younger age, shorter prothrombin time, lower levels of bilirubin in baseline studies, and decrease in bilirubin on day 14, all (P<0.001). Death due to hepatorenal syndrome occurred less frequently for the combination group at 6 months (9% vs 22%, P=0.02) and infections were also less frequent in the combination group as well (P=0.001). Six-month survival, the primary outcome, was not improved in conclusion.
- Acetylcysteine has been hypothesized to be beneficial in Parkinson's disease. It is currently undergoing clinical trials.
- Addiction to certain addictive drugs (e.g., cocaine, heroin, alcohol, and nicotine) is correlated with a persistent reduction in the expression of excitatory amino acid transporter 2 (EAAT2) in the nucleus accumbens (NAcc); the reduced expression of EAAT2 in this region is implicated in addictive drug-seeking behavior. In particular, the long-term dysregulation of glutamate neurotransmission in the NAcc of addicts is associated with an increase in vulnerability to relapse after re-exposure to the addictive drug or its associated drug cues. Drugs that help to normalize the expression of EAAT2 in this region, such as N-acetylcysteine, have been proposed as an adjunct therapy for the treatment of addiction to cocaine, nicotine, alcohol, and other drugs.
References
External links
- U.S. National Library of Medicine: Drug Information Portal - Acetylcysteine
Source of the article : Wikipedia
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