Ipratropium bromide. Molecular model of the anticholinergic drug ipratropium bromide (C20.H30.Br.N.O3). This is used for the treatment of chronic obstructive pulmonary disease and acute asthma. It acts by blocking acetylcholine receptors. Atoms are represented as spheres and are colour-coded: carbon (grey), hydrogen (white), nitrogen (blue), oxygen (red) and bromine (brown, bromine ion at top left).