Dry-powder inhalers: evaluation of testing methodology and effect of inhaler design

Process for overcoming drug retention in hard gelatin inhalation capsules

The quantity and consistency of drug delivery from dry powder inhalation devices that incorporate a pre-measured dose in a hard shell capsule of gelatin or other compatible material can be negatively affected by mold release lubricants used in capsule manufacturing. This paper describes a novel process employing supercritical CO2 for selective extraction of the fraction of lubricant responsible for the observed high and inconsistent drug retention in capsules and the ensuing lack of reproducibility of drug delivery. The process allows for lubricant removal from seemingly inaccessible interior surfaces of assembled capsule shells without altering the structural or chemical properties of the capsules. Diffusion limitations are overcome through repeated pressure increase and decrease to generate significant convective flow of dissolved lubricant out of the capsule. Drug retention is alleviated only if nearly all the retentive fraction of the lubricant is removed. The effect of extraction with supercritical CO2 on the structure of the internal surfaces of the capsules is investigated using scanning electron microscopy. Key performance parameters such as drug and carrier retention and fine particle mass are investigated using simulated inhalation tests. Laboratory and pilot scale extractions yielded similar results.

Time-of-flight aerodynamic particle size analyzers: their use and limitations for the evaluation of medical aerosols

Time-of-flight (TOF) aerosol analyzers are a class of instruments that measure the aerodynamic diameter of individual particles following a controlled acceleration in a well-defined flow field. Two instruments have been used to analyze the size of medical aerosols: Aerosizer particle size analyzer (TSI Particle Instruments/Amherst, Amherst, MA), Aerodynamic Particle Sizer (APS) aerosol spectrometer (TSI) Both instruments are capable of sizing several thousand particles a second, making it possible to obtain aerodynamic particle size distributions in a few seconds compared with up to 1 hour per measurement using compendial methods that are based on either the multistage liquid impinger or cascade impactor. This rapidity makes TOF analysis attractive for product development, as many different variables can potentially be investigated during a short period of time. The data thus obtained should be used with caution, however. Several issues, most notably the lack of a direct relationship with the mass of drug substance present and the vulnerability of the measurements to coincidence effects when sampling concentrated aerosols, may severely limit the value of data from many aerosol delivery systems, especially pressurized metered dose inhalers (pMDIs). A review of the literature illustrating the issues that are involved and providing guidance on the most appropriate uses of these analyzers is presented.