pMDIs (323)
How does the Autohaler work?
- lifting lever on top of inhaler triggers a vane - Inhalation moves the vane which releases a spring that in turn actuates the device to release the dose
What are the advantages of pMDI compared to dry powder inhaler?
1) Aerosol formation in independent of inhalation effort 2) Often better dose uniformity 3) Regulatory approval time shorter 4) Better protection against moisture and pathogens 5) Performance is independent of ambient humidity 6) Same handling and inhalation technique for all pMDIs 7) Relatively inexpensive
What are the advantages of pMDI compared to nebulizers
1) Compact, portable, robust, convenient, unobtrusive 2) Multi-dose 3) Shorter treatment time 4) Easier to prepare for treatment 5) Lower dose required 6) Relatively inexpensive
What are 5 disadvantages of spacers?
1) Cost 2) Not convenient - bulky, less portable 3) Requires cleaning 4) Optimal technique not known for many spacers 5) May not fit all actuators
Describe the 4 steps in the production of aerosolized particles from a pMDI.
1) Depression of the canister opens the metering chamber to the atmosphere; the low atmospheric pressure causes the LGP to rapidly expand and evaporate ("flash") 2) Flashing of the LGP ejects the liquid out of the sump and orifice, shearing the liquid stream into aerosolized droplets 3) As the droplets travel, the LGP completely evaporates causing size reduction and rapid solidification of the drug particles (and cooling sensation or freon effect) 4) Release of the canister results in refilling of the metering chamber
What are 3 results of using a spacer device?
1) Easier to coordinate actation and coordination 2) Allows particle size to decrease 3) Traps large particles
What are the 4 characteristics of pMDIs?
1) Multidose and versatile 2) Drug is expelled in a metered volume of LGP from pressurized container 3) Formulations are solutions or suspensions 4) Particle sizes range between 0.5-5mcg
What are the disadvantages of pMDI
1) NO breath actuation 2) No dose counter 3) Low lung deposition and high oropharyngeal deposition 4) Not suitable for large doses - valve clogging, particle aggregation, insolubility 5) Challenging to formulate 6) Performance may depend on ambient temperature 7) Present models need priming 8) HFAs still have small potential for global warming
What are 3 advantages of spacers?
1) Reduce actuation/inhalation dys-coordination 2) Reduce systemic and local side effects (irritation, dysphonia, thrush) 3) Larger drug dose delivered to lungs as compared to pMDI alone
What are the 8 steps of proper pMDI technique
1) Remove cap and shake device (if suspension) 2) Hold upright and breath out fully 3) Hold mouthpiece between lips, or 3-4cm in front of open mouth (longer distance = smaller particles) 4) Depress canister while inhaling slowly and deeply (helps deposition) 5) Hold breath for 10sec or as long as possible (helps deposition) 6) Breathe out slowly (don't exhale particles) 7) Wait approximately 1 min between doses 8) If dosing with ICS rinse mouth
How many actuations does a pMDI device provide?
100-400
What is the dose range per actuation from a pMDI?
10mcg - 5mg
What is the typical volume of the metering valve in a pMDI
25-63 microLitres
What is unique about the nozzle of an pMDI?
An atomization nozzle that atomizes dose over 0.1 - 0.5 sec
Give an example of a breath activated pMDI
Autohaler
What is problem with Freon effect for patient?
Cooling sensation - pt stops inhaling when propellant hits throat
What is the impact of ethanol in pMDI solution formuation
Lowers vapour pressure - won't boil as fast = bigger droplets
What is a major drawback of pMDIs?
Poor lung deposition - 10-15% with CFC - ~50% QVAR
What do spacers do?
Slow aerosol velocity Increase transit time between actuator and mouth
What is the role of ethanol in pMDI formulation with oleic acid?
Solvent for oleic acid
What is the role of citric acid in Atrovent HFA?
anti-oxidant
What is the role of ethanol in QVAR (solution)?
solvent
What is the role of oleic acid in pMDI?
wetting agent/dispersant
