In vitro aerosol performance and dose uniformity between the Foradile Aerolizer and the Oxis Turbuhaler

Dry powder inhalers for eformoterol fumarate dihydrate, a long-acting beta-2 agonist for bronchodilation, are currently available as the Foradile Aerolizer and the Oxis Turbuhaler. The two products are different in the formulation, the aerosol production mechanism, and the device resistance to air flow. These disparities are likely to lead to different aerosol characteristics. Our objective was to compare the in vitro performance of these two inhalers in producing eformoterol aerosols. Emitted dose uniformity was measured using a sampling apparatus described in the British Pharmacopaeia. Ten individual doses (dose number 2, 3, 15, 16, 30, 31, 45, 46, 59, and 60) of the entire content (60 doses) were collected from the Aerolizer and the Turbuhaler (six inhalers each). Particle size distribution of the aerosols generated by the two inhalers were measured by a multiple stage liquid impinger at four different air flows (30-120 L/min). Eformoterol collected from the sampling devices was measured by HPLC. Fine particles are those of < or = 1.7-5.0 microm in size in the aerosols obtained by interpolation of the data at the specified air flow. The Aerolizer showed a slight dependence of the emitted dose on the air flow, with the average emitted dose increased from 80% (at 30 L/min) to 90% (at higher flows) of the 12-microg label claim as compared with 60% for the Turbuhaler. When the emitted dose was normalized by the average emitted dose value, the Aerolizer showed less variation in the normalized emitted dose uniformity than the Turbuhaler. At high air flows, 90 and 120 L/min, both inhalers produced similar amounts (4 microg) of fine particles in the aerosol per dose discharged. As the flow as decreased to 30 and 60 L/min, both inhalers produced significantly less fine particles (p < 0.05), with the Oxis Turbuhaler producing lesser amounts than the Foradile Aerolizer. However, due to the different device resistance, comparing the inhaler performance at the same inspiratory effort may be more appropriate. At a comfortable effort of 40 cm H2O, the Foradile Aerolizer would produce a significantly higher fine particle mass in the aerosols. We conclude that the two inhalers were dissimilar in the emitted dose uniformity. The fine particle mass of eformoterol produced by the two inhalers was equivalent at high but not at low air flows. The disparities may be due to the difference in the formulation and the aerosol generation mechanism of the inhalers.