The IV injection and inhalation preparations are generally prescription only, while oral solution is available over the counter in many countries.

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.

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 tracheostomy care. It is considered ineffective in cystic fibrosis (Rossi, 2006). 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 overdose

Intravenous acetylcysteine is indicated for the treatment of paracetamol (acetaminophen) overdose. Oral acetylcysteine for this indication is uncommon as it is poorly tolerated owing to the high doses required (due to poor oral bioavailability), unpleasant taste/odour and adverse drug reactions (particularly nausea and vomiting).

For this indication, acetylcysteine acts to augment glutathione reserves (depleted by toxic paracetamol metabolites) in the body and, together with glutathione to directly bind to toxic metabolites. These actions serve to protect hepatocytes in the liver from toxicity due to paracetamol overdose.

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 (Tepel et al 2000), while others appear to cast doubt on its efficacy (Hoffman et al., 2004; Miner et al., 2004) Nevertheless, acetylcysteine continues to be commonly used in individuals with renal impairment to prevent the precipitation of acute renal failure.

Other uses

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