Effect of oropharyngeal length in drug lung delivery via suspension pressurized metered dose inhalers.

Purpose: To determine the effect of the oropharyngeal length in adults on the lung dose of a suspension pressurized metered dose inhaler, and whether employing small volume spacers can alter this role.

Methods: Depositions of Ventolin Evohaler (100) microg in the oropharyngeal models of two healthy adult subjects with 17.1 cm (short cast) and 19.9 cm (long cast) centerline lengths via three small volume spacers [two spacers with 3 cm effective length but one with 6.5 cm2 (L3) and the other with 24.6 cm2 (L3W) cross sections, and the Optimiser] were studied.

Results: Without using spacers, lung dose of the long cast (19.52 +/- 2.32 microg, mean +/- standard deviation) was significantly larger than that for the short cast (8.08 +/- 1.01 microg, p < 0.006). However, using the L3 spacer with the short cast made the lung dose (18.59 +/- 3.33 microg) similar to that for the long cast alone. Lung doses of the short cast (20.43 +/- 1.42 microg) and the long cast (30.81 +/- 1.84 microg) with the L3W spacer were similar to those with the L3 spacer. However, using the Optimiser spacer increased the lung dose for the short cast (22.27 +/- 6.03 microg) and significantly for the long cast (35.61 +/- 2.19 microg, p < 0.006) compared to those for the L3 spacer. Using spacers increased drug deposition in the oropharynx part of the short cast, and this reduced the lung dose compared to that for the long cast.

Conclusion: The oropharyngeal length in adults may affect the lung dose via the pMDIs, which may not be eliminated by using small volume spacers.