The inhaler, or pressurised metered-dose inhaler (pMDI), is a well-known medical device commonly used to help people all over the world with conditions such as asthma. However little is known about the form and phase of particles ejected from the inhaler on their route from the inhaler to the lung. It is important to understand the way that the solid particles behave once they are discharged from an inhaler as the size of a particle affects where it is delivered in the respiratory tract, ultimately determining the efficacy of the treatment.
Experimental setup used to trap and study particles discharged from a Salamon® inhaler.
In a collaboration between the University of Cambridge, Imperial College London, the University of Birmingham and the Central Laser Facility in Oxford, Tong et al. have used an optical trap to stably suspend individual particles discharged from a Salamon® inhaler for the first time. After stably trapping the particles the authors were able to determine the phase of the particles by comparing them to both a solid crystalline sample and nebulised aqueous droplets of the drug used in the Salamon® inhaler (salbutamol sulphate). Particles were also trapped and studied after being passed through a humidity chamber designed to mimic the lungs.
When first dispensed from the inhaler the particles had analogous properties to the solid crystalline sample of the drug. As the particles were exposed to a higher humidity they became more spherical as they absorbed water from the environment around them. Particles trapped at a relative humidity >92% had properties very similar to that of nebulised aqueous droplets of the drug. This change in morphology of the particles was confirmed by a combination of Raman spectroscopy and brightfield images.
Tong et al. have been able to show that once released into the body the crystalline particles take up water, causing the particles to increase in size and sphericity. This information will be of great aid in understanding and improving the efficiency of aerosol-based inhalation products.
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Rapid interrogation of the physical and chemical characteristics of salbutamol sulphate aerosol from a pressurised metered-dose inhaler (pMDI)
H.-J. Tong, C. Fitzgerald, P. J. Gallimore, M. Kalberer, M. K. Kuimova, P. C. Seville, A. D. Ward and F. D. Pope
DOI: 10.1039/c4cc05803h
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