Oxitropium bromide is an mAChR antagonist used as an anticholinergic bronchodilator drug for the treatment of asthma and chronic obstructive pulmonary disease. IC50 & Target: mAChR^[1] In Vitro: Oxitropium bromide is a muscarinic antagonist which blocks musucarinic acetylcholine receptors (mAChR). Incubation with oxitropium bromide of untreated diaphragm muscle and diaphragm muscle injected with endotoxin does not increase the force-frequency curves dose-dependently in vitro; however, it causes both types of muscle to be fatigue resistant^[1]. In Vivo: Oxitropium bromide inhalation shifts force-frequency curves upward at 2 h after inhalation and inhibits the decrease of force-frequency curves due to endotoxin injection in vivo^[1]. Oxitropium bromide strongly and persistently inhibits the acetylcholine (ACh)-induced resistance. The increase in resistance induced by histamine, serotonin, leukotriene D4 or antigen is prevented by oxitropium bromide oxitropium bromide^[2]. Inhalation of the anticholinergic agent oxitropium bromide at doses of 1.5 μg and higher greatly attenuates the decrease in mucus score produced by intravenous histamine but not by inhaled histamine^[3].