An Investigation of Carrier Particle Type, Electrostatic Charge and Relative Humidity on In‐vitro Drug Deposition from Dry Powder Inhaler Formulations

Deep lung deposition from dry powder inhaler (DPI) devices represents a small proportion (5–16% w/w) of the drug dose. In this work, some of the factors which may affect drug delivery, for example, carrier excipient type, electrostatic charge and relative humidity, have been investigated using a cascade impactor. The respirable fraction of salmeterol xinofoate was affected by excipient type and relative humidity of inspired air. The lactose formulation produced a higher respirable fraction than formulations containing sucrose or spray-dried sorbitol. Inspired air (r.h. 97–99%) reduced the respirable fraction for each drug-excipient formulation when compared with experiments using ambient conditions. The percent (w/w) drug retained in the DPI was also dependent on excipient type (32% for lactose, 57% for spray-dried sorbitol and 71% for sucrose formulations at 97–99% r.h. inspired air). The respirable fraction of lactose formulations was reduced by electrostatic charging of the drug and carrier particles before DPI filling, whereas that for sucrose and sorbitol spray-dried formulations was unaffected. The results indicate that carrier excipient type, relative humidity and electrostatic charging can have an effect on in-vitro drug deposition and further detailed investigations should be undertaken in relation to DPI formulation and use.