Protective effect of Duovent on bronchospasm induced by carbachol in comparison with each of its components

The protective effect on bronchospasm, induced by carbachol, of 2 puffs of fenoterol (200 micrograms), ipratropium bromide (80 micrograms) and Duovent (200 micrograms fenoterol + 80 micrograms ipratropium bromide) was compared in a group of 12 asthmatic patients. The double-blind study was always performed at the same time of day, 2 and 5 h after premedication, on 4 consecutive days. After the 1st day, when placebo was given, the drugs were administered randomly. As regards PD20 FEV1 (dose of carbachol necessary to determine a 20% decrease in FEV1), Duovent was found to be the most active drug. A very clear difference was seen 2 h later, not only compared to fenoterol (PD20 placebo, means +/- SD: 90.8 +/- 93.2 micrograms; PD20 Duovent: 1,876.5 +/- 1,103.5 micrograms; PD20 fenoterol: 324.3 +/- 220.7 micrograms) but also with ipratropium bromide (PD20: 1,215.8 +/- 950 micrograms). After 5 h, the three treatments maintained a significant action, but the efficacy of Duovent, while significantly greater than that of fenoterol, was very similar to that of ipratropium (PD20 placebo: 78.4 +/- 92.6 micrograms; PD20 fenoterol: 134.6 +/- 138.2 micrograms; PD20 ipratropium bromide: 295.4 +/- 337 micrograms; PD20 Duovent: 286.7 +/- 181.2 micrograms).