Ambroxol-d5 is intended for use as an internal standard for the quantification of ambroxol by GC- or LC-MS. Ambroxol is an expectorant and active metabolite of bromhexine. It decreases short-circuit currents in electrically stimulated isolated canine tracheal epithelial cells when applied submucosally. Ambroxol decreases IL-13-induced production of mucin 5AC (MUC5AC) in primary human airway epithelial cells and inhibits IL-13-induced decreases in the mucociliary transport rate of endogenous particles in the same cells. Ambroxol increases phenol red secretion, a marker of expectorant activity, in mice when administered at doses of 30, 60, or 120 mg/kg. Formulations containing ambroxol have been used in the treatment of acute or chronic respiratory conditions.