Estimation of the Deposition of Aerosolized Drugs in the Human Respiratory Tract Due to Hygroscopic Growth

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Abstract
Hygroscopic aerosol particles will grow in the human respiratory tract due to the nearly saturated air. A calculation method had been developed previously to estimate the growth and the deposition in the human respiratory tract of salt particles. This method is adapted here to estimate the growth and the deposition of particles of three drugs during respiration. The relative growth of drug particles is comparable to the growth of salt particles, where different drug particles change their size by a factor of 2.2– 3.5, and salt particles by a factor of 2.0-4.4. Likewise, the deposition in the bronchial and pulmonary regions is enhanced for particles with initial sizes in the range of 0.3-5 μm for both the drug and salt particles. The increase in deposition is about a factor of 2 for particles with initial sizes between 0.5-2 μm. Also, the maximum values for deposition in the bronchial and pulmonary regions at initial particle sizes between 2-4 μm are increased by up to 20% compared to the values for stable particles. An equation is proposed to estimate the deposition of an arbitrary aerosolized drug particle in the bronchial and pulmonary regions. We conclude that the hygroscopicity of drug particles is an important factor for estimating their deposition in the human respiratory tract.