Dry powder inhalers have become increasingly attractive for pulmonary delivery of locally and systemically effective medications. In comparison to the liquid counterparts, such as nebulisation and pressurised metered dose inhalers, the powder form generally offers better chemical stability, improved portability and potentially superior patient adherence. Currently, the aerosol performance between dry powder inhalers varies to a large extent due to differences in the design of inhaler device and formulation. The particulate properties have a significant influence on the inter-particle interactions, which impacts on the aerosolisation of the inhaled powder. In this review, critical particulate properties that affect aerosol performance are discussed. Recent advances in powder production and particle engineering techniques are also assessed, aiming to develop new inhaled powder formulations or improve the aerosolisation efficiency of existing products.

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Cohesive powders are problematic in the manufacturing of pharmaceutical solid dosage forms because they exhibit poor flowability, fluidization and aerosolization. These undesirable bulk properties of cohesive powders represent a fundamental challenge in the design of efficient pharmaceutical manufacturing processes. Recently, mechanical dry coating has attracted increasing attention as it can improve the bulk properties of cohesive powders in a cheaper, simpler, safer and more environment-friendly way than the existing solvent-based counterparts. In this review, mechanical dry coating techniques are outlined and their potential applications in formulation and manufacturing of pharmaceutical solid dosage forms are discussed. Reported data from the literature have shown that mechanical dry coating holds promise for the design of superior pharmaceutical solid formulations or manufacturing processes by engineering the interfaces of cohesive powders in an efficient and economical way.

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