A model for the analysis of membrane-type dissolution tests for inhaled drugs.

Impactor-type dose deposition is a common prerequisite for dissolution testing of inhaled medicines, and drug release typically takes place through a membrane. The purpose of this work is to develop a mechanistic model for such combined dissolution and release processes, focussing on drug that initially is present in solid form. Our starting points are the Noyes-Whitney (or Nernst-Brunner) equation and Fick's law. A detailed mechanistic analysis of the drug release process is provided and approximate closed-form expressions for the amount of drug that remain in solid form and the amount of drug that has been released are derived. Comparison with numerical data demonstrated the accuracy of the approximate expressions. Comparisons with experimental release data from literature demonstrated that the model can be used to establish rate-controlling release mechanisms. In conclusion, the model constitutes a valuable tool for the analysis of in vitro dissolution data for inhaled drugs.