[Bronchial expectorants : pharmacology of bronchial mucomodifiers]

Prescription of bronchial mucus modifiers has benefited from recent advances in the knowledge of biochemical constituents of bronchial fluids, their regulation and disturbances on the one hand, and the consequences of biochemical changes in these fluids on rheological characteristics of bronchial secretions on the other. In addition, the significance of these characteristics has been evidenced by the study of mucociliary transportation. Drugs which modify bronchial fluids are studied according to their mode of action upon the organized gel phase, mobilized by ciliary activity, and the aqueous sol phase, which enables this ciliary activity. Drugs which modify the gel phase are either true mucolytic agents or muco-regulators. True mucolytic drugs include reducing agents with a free thiol group, chiefly N-acetyl-cysteine which breaks disulfide bonds linking different protein chains, and proteolytic enzymes which break protein chains. The latter also have an appreciable anti-inflammatory effect but are rarely used at present owing to allergic reactions. Mucoregulating drugs are cysteine derivatives whose thiol group is not free. They are headed by carbocysteine which activates the synthesis of sialidized acid mucins. They enable reorganization of bronchial mucus, reversing former drops in viscosity and elasticity, thereby improving mucociliary transportation. They have a complementary anti-inflammatory action.