Quantification of the synergism between fenoterol and ipratropium bromide in the counteraction of experimental bronchospasm.

The interaction between the beta 2-agonist fenoterol and the antimuscarinic ipratropium bromide in the counter-action of experimental bronchospasm in the guinea-pig was studied qualitatively and quantitatively. Finney's analysis showed a significant overadditive interaction between the two constituents of the association, the 'overadditivity factor' being 2.15 if calculated on the peak activity or 2.68 if calculated on the area under the curve inhibition-time. In addition, the combination possesses both of the advantages of the two components, namely rapid onset of action (characteristic of the beta-agonist) and long duration of action (characteristic of the antimuscarinic). A study of the principal cardiovascular and hemodynamic parameters in the cat ruled out any synergism between the two drugs at these levels.