Pharmacology: Pharmacodynamics: Acetylcysteine is a mucolytic, expectorant drug, derivative of cysteine amino acid. Due to presence of free sulfhydryl group, acetylcysteine breaks disulfide bonds of mucoproteins leading to decrease in the viscosity of bronchial mucous. It relieves sputum discharge due to increase of mucociliary clearance. Acetylcysteine also has antioxidant and pneumoprotective properties, this is due to the ability of sulfhydryl groups to bind free radicals. Besides, acetylcysteine stimulates the increase of glutathione, which is an important factor of detoxification. This property of acetylcysteine gives a potential to use it as an antidote in acute intoxications of Paracetamol and other substances (aldehydes, phenols, etc).
Pharmacokinetics: After oral administration, acetylcysteine is rapidly and almost fully absorbed in the digestive tract. The bioavailability of acetylcysteine after oral administration is about 10%. Maximal concentration after oral administrations achieved in 1-3 hours.
In the liver, it is metabolized to cysteine (pharmacologically active metabolite) and diacetylcysteine, cystine and so on until mixed disulphides. In the body, acetylcysteine and its metabolites are determined in various forms: partially-as free substance, partially-flowing to blood plasma proteins, partially-as incorporated amino acids. It is practically fully excreted as inactive metabolites (inorganic sulphates, diacetylcysteine) with urine. Only small amount of acetylcysteine is excreted unchanged with feces. The blood plasma half-life is approximately 1 hour and depends on biotransformation rate of liver.