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Review
. 2024 Feb;44(2):109-114.
doi: 10.1007/s40261-023-01330-2. Epub 2024 Jan 10.

Demystifying Dry Powder Inhaler Resistance with Relevance to Optimal Patient Care

Toby G D Capstick  1 , Sanjay Gudimetla  2 , David S Harris  3 , Rachel Malone  2 , Omar S Usmani  4
Affiliations
Review

Demystifying Dry Powder Inhaler Resistance with Relevance to Optimal Patient Care

Toby G D Capstick et al. Clin Drug Investig. 2024 Feb.

Abstract

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.

Plain language summary

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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Conflict of interest statement

TGDC is a member of the UK Inhaler Group and has received non-financial support from Napp for attendance at ERS conference; TGDC’s employer has received payment for his participation in advisory boards or for providing teaching sessions from AstraZeneca, Chiesi, GSK, Novartis, Boehringer Ingelheim and Insmed, outside the submitted work. SG and RM are employees of Chiesi Ltd, UK. DSH is a member of Drug Delivery to the Lungs organising committee since 2013 (unpaid). OSU reports grants and personal fees from AstraZeneca, Boehringer Ingelheim, Chiesi and GlaxoSmithKline; grants from Edmond Pharma; personal fees from NAPP, Mundipharma, Sandoz, Takeda, Cipla, Covis Pharma, Novartis, Mereo BioPharma, OrionPharma, Menarini, UCB, Trudell Medical, Deva Pharmaceuticals, Kamada and Kyorin, outside the submitted work.

Figures

Fig. 1
Fig. 1
Impact of high versus low dry powder inhaler (DPI) resistance on differential pressure. DPI resistance (√Pa min L −1) is defined as the ratio of the square root of the differential pressure (Pa) across it to the flow rate through it.
Fig. 2
Fig. 2
Inspiratory power curves for adults and children against volumetric flow rate (A) demonstrating the non-linear relationship between airflow and power, with maximum power achieved below maximum airflow. The power for deagglomeration of the active substance is generated by the patient’s inspiratory manoeuvre. As power is the result of flow rate and differential pressure, inhalers must have some resistance for there to be power in the airflow through them. Estimated operating points of dry powder inhalers (DPIs) when used by healthy adults and children (B). Pressure-flow curves of three example DPIs and average operating points for adults and children are shown, illustrating that healthy adults can achieve higher pressure drops than healthy children. Cyclohaler® (Plastiape S.p.A., Osnago LC, Italy) is a low-resistance DPI, Advair® Diskus® (GSK, Brentford, UK) is a medium-resistance DPI and HandiHaler® (Boehringer Ingelheim, Ingelheim, Germany) is a high-resistance DPI. Reproduced with permission from Harris D. The Advantages of Designing High-Resistance Swirl Chambers for Use in Dry-Powder Inhalers. ONdrugDelivery Magazine, Issue 57 (Apr 2015):10–13.
See this image and copyright information in PMC

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