Evidence of overadditive interaction between fenoterol and ipratropium bromide in the counteraction of cholinomimetic-induced tracheobronchial contractions.

A study was made of the pharmacological interaction between two bronchoselective antispasmodics, the beta2-agonist fenoterol and the antimuscarinic ipratropium bromide, in the counteraction of tracheobronchial smooth muscle contractions. Both the in vitro (isolated guinea-pig trachea stimulated by carbachol) and the in vivo experiments (bronchospasm induced by acetylcholine in the guinea-pig) pointed to an overadditive interaction. The evidence for a synergistic antagonism against cholinergic stimulation points to the potential value of the association between fenoterol and ipratropium bromide in the treatment of bronchial asthma, especially in view of the important role that the cholinergic system seemingly plays in this distance.