It has been documented that tiotropium is less likely to induce oxygen desaturation in stable COPD patients compared to long-acting beta2-agonists (LABAs) and combined administration of a LABA and an inhaled corticosteroid (ICS) reduces the potential for acute effects of LABA on blood-gas tensions. In this study, we have compared the acute effects of tiotropium 18 microg and salmeterol/fluticasone combination (SFC) 50/250 microg on arterial blood gases in 20 patients with stable COPD. Each subject was studied on 2 days, separated from one another by at least 4 days. Blood specimens were taken just before the inhalation and at 15, 30, 60, 180 and 360 min after inhalation of each treatment, and spirometry was performed at the same time points. As expected, both treatments significantly improved FEV1 (greatest changes were 0.20 L, 95% CI: 0.13-0.27 at 360 min after tiotropium; and 0.13 L, 95% CI: 0.06-0.19 at 180 min after SFC). The greatest mean changes from baseline in PaO2 were -1.7 (95% CI: -4.0 to 0.6)mmHg, p=0.134, after tiotropium; -0.8 (95% CI: -2.2 to 0.6)mmHg, after SFC. Both changes were observed after 15 min. Both drugs caused a small decrease in PaCO2 (greater changes: -1.9 (95% CI -3.2 to -0.6)mmHg, p=0.005 at 60 min after tiotropium; and -2.4 (95% CI: -3.5 to -1.3) mmHg, p=0.0002 at 180 min after SFC). These results indicate that both tiotropium and SFC are able to induce a significant long-last bronchodilation without affecting arterial blood gases. Moreover, they confirm that the impact of tiotropium on PaO2 is small and without clinical significance and the addition of a LABA to an ICS can reduce the potentially dangerous acute effect of the LABA on blood gases.
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