Variability in lung deposition of inhaled drug, within and between asthmatic patients, with a pMDI and a dry powder inhaler, Turbuhaler.

In vitro analysis of inhaled formulations measures, among other parameters, the variability in delivered dose, while a corresponding in vivo analysis also includes the variability caused by patient performance and distribution of drug between the oropharynx and the lungs. In vitro, the dose variability is higher for Turbuhaler(R) than for the corresponding pMDI, whereas in vivo, the converse is true: the variability in lung deposition is significantly higher, both between and within subjects, for pMDI than for Turbuhaler. The observation can be due to several factors such as the non-continuous working principle of inhalation via pMDI as opposed to the continuous working principle of inhalation via Turbuhaler.