Characteristics of inhaler devices3,7

Device typeMechanism of action
HFA pMDIPressurized suspension of micronized drug particles distributed in propellant; others are ethanolic solutions
Precise amount (20–100 μL) dispensed with each press of canister
Shaking not required as with CFC pMDIs
Pressing canister releases drug
Breath-actuated pMDIPressurized canister with flow-triggered system driven by a spring
Inhalation drives spring to trigger inhalation
Requires higher PIF than HFA pMDIs, but lower than DPIs
DPIDry powder inside capsule (manual loading) or inside device
Micronized drug particles (1–5 μm) blended with inactive excipient (40 μm) or used alone
Inhalation deaggregates medication particles and disperses them within airways
Minimum PIF rate required for deaggregation (varies by DPI device)
Passive (breath-actuated)
Drug stored inside cartridge (loaded on first use)
Spring releases dose into micropump; dose released when button is pressed "Uniblock" passes dose through minute channels releasing jet streams of drug solution
Breath-enhanced jet nebulizerAir stream moves through jet causing drug solution to be aerosolized; powered by compressor
Additional room air taken into nebulizer during inhalation drives aerosolization
Nebulizer drug solution cools during nebulization
Vents the expired air outside device
Tabletop and portable models available
Breath-actuated jet nebulizerAir stream moves through tube causing drug solution to be aerosolized; powered by compressor
Patient inhalation drives aerosolization (does not occur unless patient inhales)
Tabletop and portable models available
Ultrasonic nebulizerPiezoelectric crystals vibrate causing aerosolization
Nebulized drug solution gets heated during nebulization
Vibrating mesh nebulizerPiezoelectric crystals vibrate a mesh plate causing aerosolization
Very fine droplets
No significant change in temperature of the solution during nebulization
Lower residual drug remaining in chamber compared with jet nebulizers
  • Abbreviations: CFC, chlorofluorocarbon; DPI, dry powder inhaler; HFA, hydrofluoroalkane; PIF, peak inspiratory flow; pMDI, pressurized metered-dose inhaler; SMI, soft mist inhaler.