Inhaled Drugs

In the case of inhaled and nasal drug delivery products, the first prerequisite is to deliver an appropriate amount of drug to the target site. For that reason,in vitro testing is concentrated on drug delivery (emitted dose) and lung or nasal deposition (aerodynamic particle size distribution) using a cascade impactor such as the Next Generation Impactor (NGI) or Andersen Cascade Impactor (ACI) as opposed to dissolution or drug release.

Once deposited, the absorption or lung uptake, and hence the therapeutic effectiveness of the drug, depends on the active dissolving in the small amounts of aqueous fluid and lung surfactant available at the target site.

Based on a concept developed by Professor Jason McConville at the University of Texas, the NGI Dissolution Cup and Membrane Holder incorporates a modification of the standard NGI cup which allows size fractionated particles from an aerosol cloud to be collected and then tested in a conventional dissolution tester.

A similar technique can be employed using the Andersen Cascade Impactor, in this case, by applying a 76 mm polycarbonate filter to the collection plates prior to analysis, such that the drug is captured directly on the membrane, and then sandwiching the inverted membrane between the glass and PTFE surfaces of the watch glass/PTFE Assembly normally used for transdermal patches.

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