Mechanism of action erdosteine, an orally mucolytic agent. erdosteine is a thiol derivative developed for the treatment of chronic obstructive bronchitis, including acute infective exacerbation of chronic bronchitis. erdosteine contains 2 blocked sulfhydryl groups which are released following first-pass metabolism. the 3 active metabolites exhibit mucolytic and free radical scavenging activity. erdosteine modulates mucus production and viscosity and increases mucociliary transport, thereby improving expectoration. it also exhibits inhibitory activity against the effects of free radicals produced by cigarette smoke. clinical studies in patients with chronic obstructive lung disease have demonstrated the efficacy and tolerability of erdosteine. erdosteine 300mg twice daily reduced cough (both frequency and severity) and sputum viscosity more quickly and more effectively than placebo and reduced the adhesivity of sputum more effectively than ambroxol 30mg twice daily.