One must draw attention to the impressive effects of tiotropium. It is probably the most potent bronchodilator yet for COPD. In part, its potency may be attributed to its unique selectivity for M1 and M3 muscarinic receptors, a feature that ipratropium and all other available antimuscarinic agents lack. With a nominal duration of action of 24 h, and probably much longer,13–
tiotropium is by far the longest-acting bronchodilator of any class. Apart from the convenience of once-daily dosing for patients, the long duration of action ensures that significant bronchodilation is maintained around the clock. If patients use tiotropium consistently, their FEV1 would never fall to baseline. Out of interest, one can calculate the potential magnitude of this effect in relation to the natural decline in lung function from data provided in Table 3. The trough FEV1 increased by a mean of 115 mL in the group that received tiotropium for 1 year, while that of subjects who received placebo declined by 38 mL, giving an overall treatment effect of 153 mL. If the mean annual decline in FEV1 of this population is 38 mL, an amount which accords with previous reports,15
then an increase in trough FEV1 of 153 mL due to tiotropium use would correspond to the amount the FEV1 would otherwise be expected to decline in 153/38 years, approximately 4 years. It would be as if their FEV1 had been restored to its level 4 years previously. This calculation is quite speculative, of course, and it cannot be said that patients will survive 4 years longer if they use tiotropium; there are no data on the effects of tiotropium on survival at this time. Nor are there definitive data that use of tiotropium decreases the rate of decline of lung function or the frequency of important events such as acute exacerbations; such studies are ongoing. But the data do suggest that tiotropium will become an important addition to our therapy for this common and highly symptomatic disease.