A human oral-throat cast integrated with a twin-stage impinger for evaluation of dry powder inhalers

The aim of this study was to investigate the applicability of replacing the glass throat from a twin-stage impinger (TSI) with a human oral-throat cas t. Monodisperse aerosols were used to calibrate the human oral cast-TSI at 60 L min(-1) and cut-off in particle size was compared with that of the TSI described in the British Pharmacopoeia which employs a glass throat. The a mount of salbutamol sulphate land lactose) delivered by the Cyclohaler depo siting on various elements of the in-vitro model were determined. The calibration of the model containing a human oral-throat cast at 60 L mi n(-1) gave a particle size cut-off of 5.2 mu m which was less than that of the TSI (6.3 mu m). The oral-throat cast trapped more drug than the glass t hroat model with a formulation that employed the larger carrier (63-90 mu m ; P<0.05) while it trapped a lesser amount of drug with those filled with t he lower size carrier (Lactochem, micronised lactose). The greater amount o f lactose in the formulation that employed the larger-sized carrier (63-90 mu m) was deposited closer to the inlet of the oral-throat cast than to the inlet of the glass throat model. Replacement of the glass throat in the TSI by the human oral-throat cast, l eads to a change in deposition efficiency, with the cast having a higher fi lter efficiency and hence more aerosol particles being captured before thei r entry into the TSI. This should be investigated further to determine whet her such a model might provide a more realistic assessment of the in-vivo c haracteristics of an aerosol in comparison with the TSI currently being emp loyed, which utilises the glass throat as the portal of entry.