The selection of an inhaler device is a key component of respiratory disease management. However, there is a lack of clarity surrounding inhaler resistance and how it impacts inhaler selection. The most common inhaler types are dry powder inhalers (DPIs) that have internal resistance and pressurised metered dose inhalers (pMDIs) that use propellants to deliver the drug dose to the airways. Inhaler resistance varies across the DPIs available on the market, depending largely on the design geometry of the device but also partially on formulation parameters. Factors influencing inhaler choice include measures such as flow rate or pressure drop as well as inhaler technique and patient preference, both of which can lead to improved adherence and outcomes. For optimal disease outcomes, device selection should be individualised, inhaler technique optimised and patient preference considered. By addressing the common clinically relevant questions, this paper aims to demystify how DPI resistance should guide the selection of the right device for the right patient.
Selection of the right inhaler is important to ensure that patients with respiratory diseases get the most benefit from their treatment. Dry powder inhalers and pressurised metered dose inhalers are the most common inhaler types. Pressurised metered dose inhalers use propellants to deliver the drug to the lungs. In contrast, dry powder inhalers deliver the drug to the lungs by having internal resistance. This restricts the flow of air through the inhaler. As the patient inhales through the inhaler, the resistance against the air flow generates the power to separate the drug molecules and carry them to the lungs. While there are many factors to be considered for inhaler selection, there is often confusion around how resistance should guide selection of inhaler. With low-resistance devices, patients must inhale faster to generate the power to separate the drug molecules, which may be difficult in patients with poor lung function. With high-resistance devices, patients do not need to inhale as fast to separate the drug, and most patients can effectively use the inhaler. This article addresses the common clinically relevant questions to clarify how the internal resistance of the inhaler should be used to help guide the selection of the right device for the right patient.
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