Clinical pharmacokinetics of N-acetylcysteine.

N-Acetylcysteine is useful as a mucolytic agent for treatment of chronic bronchitis and other pulmonary diseases complicated by the production of viscous mucus. It is also used as an antidote to paracetamol (acetaminophen) poisoning and found to be effective for the prevention of cardiotoxicity by doxorubicin and haemorrhagic cystitis from oxazaphosphorines. After an oral dose of N-acetylcysteine 200 to 400 mg the peak plasma concentration of 0.35 to 4 mg/L is achieved within 1 to 2 hours. Although the data are conflicting, it appears that the administration of charcoal may interfere with drug absorption, with up to 96% of the drug adsorbed on to the charcoal. Information on absorption in the presence of food or other drugs is not available. The volume of distribution ranges from 0.33 to 0.47 L/kg and protein binding is significant, reaching approximately 50% 4 hours after the dose. Pharmacokinetic information is not available as to whether or not N-acetylcysteine crosses the blood-brain barrier or placenta, or into breast milk. Renal clearance has been reported as 0.190 to 0.211 L/h/kg and approximately 70% of the total body clearance is nonrenal. Following oral administration, reduced N-acetylcysteine has a terminal half-life of 6.25h. Little is known of the metabolism of this agent, although it is believed to be rapidly metabolised and incorporated on to proteins. The major excretory product is inorganic sulphate. Frequently reported side effects are nausea, vomiting and diarrhoea. Biochemical and haematological adverse effects are observed but are not clinically relevant. Drug interactions of clinical significance have been observed with paracetamol, glutathione and anticancer agents.