Novel temperature controlled surface dissolution of excipient particles for carrier based dry powder inhaler formulations

The surface of lactose monohydrate was modified by solution phase variable temperature dissolution. Lactose monohydrate crystals were added to a known volume of a saturated solution of lactose monohydrate at 25°C. The temperature of the mixture was then ramped to either 30, 35, 40, or 50°C to produce lactose monohydrate batches with reduced levels of fines and lower surface roughness. A dramatic decrease in surface roughness with increasing dissolution temperature was visually observed using scanning electron microscopy. Particle size analysis suggested that the level of lactose fines was reduced after treatment at the lowest dissolution temperature, 30°C. Evaluation of the samples' drug aerosolization using a twin stage impinger, after blending with salbutamol sulphate, suggested that even though there were dramatic changes in roughness and particle size distribution after surface dissolution at 30°C, there was no significant difference in aerosolization as measured by fine particle fraction. However, after surface dissolution at 35°C, there was an increase in fine particle fraction. Surface dissolution at even higher temperatures did not result in any further increase in fine particle fraction. These observations suggest that surface roughness and fines play an important role in the aerosolization of salbutamol sulphate, but the inter-relationships are not straightforward.