Mucolytic agents are drugs designed to reduce the vicosity and the adesivity of the mucus and improve its remotion either by cough, by postural draining or by mechanical means28. The first agent proposed as a mucolytic agent has been N-acetyl-cysteine. Its mucolytic action is due to the presence of free sulfydryl groups wich directly act on the mucoprotein, there by breaking disulfide bonds and thus reducing its viscosity28. Carboxymethyl-cysteine modifies the syntesis of glucoproteins of mucus, increasing the production of syaloglucoproteins. Otherwise, these proteins increase the mucociliar clearance, increasing cough effectiveness. Ambroxol is an amine derivative of dibromophenylcyclohexanol, a bromexine metabolite. It is used in the chlorydrate, the teophylinate or in the free form. Erdosteine is a thiol derivative which shows muco-regulatory and antioxidant properties. Both animal and human studies showed its capability of modulating the production and the viscosity of mucus, besides increasing the mucociliar transport. It has also been shown that erdosteine antagonizes the deleterious effects of free radical production in smoking, through an action on a1-antitrypsin activity. The penetration of antibiotics into the sputum is increased by the action of erdosteine on the reduction of bronchial secretions viscosity and/or control of bronchial inflammation. Thus, the local levels of antibiotics are increased and the therapeutic response is fastened24.