Inhaler devices

Three types of inhaler devices exist to deliver inhaled corticosteroids to the lungs:

• Pressurized metered-dose inhalers (pMDIs) – These dispense a measured dose of drug through the use of a propellant. Suspensions and solutions are both delivered using pMDIs, which, compared with DPIs, produce smaller particles of a more consistent size. Suspensions contain particles of the order 2.4μm in diameter, while solutions contain particles with an average diameter of 1.1μm. pMDIs yield high drug deposition in the lungs^1,2 and only these devices (Figure 1) are capable of producing a large fraction of fine particles that are small enough to be deposited in the small airways. As with all types of inhaler, it is important to use correct technique and coordination to ensure a consistent dose is delivered.

Figure 1: Pressurized metered-dose inhaler

• Dry powder inhalers (DPIs) – Correct inhaler technique is essential for patients to inhale an accurate dose of ICS using a DPI. This is because the particle size distribution of these inhalers may be related to the rate at which peak inspiratory flow (PIF) is achieved.³ PIF has to be reached within 1 second to ensure that a reasonable proportion of small particles is inhaled (Figure 2). Some patients may not be able to generate enough force to properly activate these devices.
  

DPI: dry powder inhaler; PIF: peak inspiratory flow

Figure 2: Particle size distribution with DPIs is influenced by inhalation technique.³

• Wet nebulizers – These devices dispense a fine mist of drug-filled droplets, which are inhaled through a mask or mouthpiece over 5–10 minutes. Nebulizers are not easily portable and are most often restricted to clinical environments.

It is important to select the correct inhaler device according to a patient’s abilities and preferences (Table 1).

pMDI: pressurized metered-dose inhaler; DPI: dry powder inhaler; SMI: soft mist inhaler
Table 1: Suitability of the main device types, categorized by patient ability⁴

References

1. Newman S, Salmon A, Nave R, et al. High lung deposition of 99mTc-labeled ciclesonide administered via HFA-MDI to patients with asthma. Respir Med 2006;100:375-84
2. Leach CL, Bethke TD, Boudreau RJ, et al. 2-D and 3-D imaging show ciclesonide has high lung deposition and peripheral distribution: a nonrandomized study in healthy volunteers. J Aerosol Med 2006;19:117-126
3. Everard ML, Devadason SG, Le Souëf PN. Flow early in the inspiratory manoeuvre affects the aerosol particle size distribution from a Turbuhaler. Respir Med 1997;91:624-8
4. Adapted from Chapman KR, Voshaar TH, Virchow JC. Inhaler choice in primary practice. Eur Respir Rev 2005;14:117-122