Acetylcysteine has a peripheral mucolytic action. It acts as an inhibitor of the irreversible thiol oxidase complex in lung epithelial cells, resulting in increased mucus clearance from airways. This enzyme catalyses the rate-limiting step in the lysis of mucus-toxin complexes by superoxide and hydrogen ions, and in addition to this, acetylcysteine prevents mitochondrial mediated apoptosis. Acebrophylline is a mucolytic and bronchodilator that promotes deeper breathing, increases oxygen delivery to the lungs, and relaxes the airways.