Characterization of pharmaceutical powder inhalers: estimation of energy input for powder dispersion and effect of capsule device configuration

Abstract

The present study was aimed to examine (i) the overall energy input ( E dispersion) into two capsule-type pharmaceutical powder inhalers, the Dinkihaler ® and the Rotahaler ®, and (ii) the effect due to the presence of capsule, on powder dispersion using mannitol as a model compound. Powder dispersion was assessed by a liquid impinger with the fine particle fraction (FPF) defined as the wt. % of particles ⩽5 μm in the aerosol. The overall energy input is given by E dispersion=Δ PV af t dispersion, where Δ P is the total pressure drop across the inhaler, V af the volume air flow through the inhaler, and t dispersion the time taken for powder to empty out of the capsule. The overall energy input, E dispersion, was found to correlate with the FPFs generated by either inhaler. Compared with the Rotahaler ® at the same air flows, the Dinkihaler ® had larger E dispersion values, due to higher Δ P and longer t dispersion. The larger E dispersion was consistent with the higher FPFs. For both inhalers, the presence of a capsule improved the FPFs, presumably via collision between the powder and capsule during dispersion. For the Dinkihaler ® the capsule-end apertures also affected the FPF, powder emptying and impaction loss. The optimal aperture size was found between 1.00 and 2.38 mm to deliver a high FPF (50– 60 wt. % ) with minimal impaction loss and capsule and device retention at a moderate air flow (0.0015 m 3/ s) .