PARTICLE-SIZE SELECTION DEVICE FOR USE WITH THE TURBOHALER

Background - Drug deposited within the upper airways of patients using dry powder inhalers does not contribute to the therapeutic effect but can result in unwanted local side effects and, when swallowed, may co ntribute to systemic effects. A chamber has been devised which uses th e centrifugal force generated by the Turbohaler to remove large ''non- respirable'' particles with a view to minimising deposition in the upp er airway. An in vitro study was performed to determine whether such a chamber could reduce the dose contained in coarse particles without h aving a significant effect on the ''respirable dose''. Methods - The m outhpiece of a 200 mu g Turbohaler was modified to allow a small volum e chamber to be attached. The particle size distribution generated by the Turbohaler was assessed using a multistage liquid impinger with a flow rate of 60 l/min. The quantity of drug on each stage was quantifi ed using an ultraviolet spectrophotometric technique. For each experim ent 10 actuations were used to ensure adequate quantities of drug on e ach stage. Particles depositing on stages 3 + 4 have a diameter of <6. 8 mu m and are arbitrarily referred to as the ''respirable dose''. The particle size distribution obtained using the Turbohaler (n = 10) was compared with that from the Turbohaler + chamber (n = 11). Results - The addition of the chamber resulted in the mean (SD) dose contained i n larger ''non-respirable'' particles depositing on stages 1 + 2 being reduced from 52.2 (12.3) to 29.6 (6.9) mu g per actuation. However, t he chamber did not affect the ''respirable'' dose. The dose contained in particles with a diameter of <6.8 mu m from the standard Turbohaler was 91.1 (8.9) mu g compared with 82.4 (18.6) mu g when used with the chamber. Conclusions - These results indicate that it is possible to devise an effective particle size selection device for the Turbohaler. It may be possible to produce such devices for other dry powder inhal ers, although the design would need to be tailored to each particular device.