Pressurised Metered Dose Inhalers and Nebulisers Flashcards
what is a pMDI?
a solid drug dissolved/suspended in a non-polar volatile propellant
how does a pMDI deliver drugs to the lungs?
- drug in solution or suspension in pressurised canister
- actuation of metering valve so pre-determined dose releases
- volume expansion of formulation so droplet released
- enters airways as fine spray droplets
- deposition depends on inspiratory flow and separation
- dissolution
- absorption into lungs
what are pMDI containers made from?
aluminium or tin-plated steel (so they’re inert)
what is used to control the dose of drug being released?
the metering valve
what is the actuator of a pMDI made of?
polyethylene or polypropylene
what is the role of the actuator?
determines shape and speed of emitted aerosol cloud
what are propellants and give examples of them?
they’re liquefied gases e.g. Chlorofluorocarbons (CFCs) and Hydrofluoroalkanes (HFA’s) (liquefied due to high pressure in canister)
why have HFA’a replaced CFCs as propellants?
as CFCs cause ozone depletion
what is the role of propellants?
provide required pressure to atomise the drug formulation into micron-scaled droplets as upon actuation the propellant expands and vaporises under ambient conditions with associated dispensing of the metred dose as an aerosol spray.
what excipients are included in a pMDI?
co-solvent (ethanol)
surfactants (tween80)
suspending agents (prevents caking of suspension)
what are the 5 key components of a pMDI?
- container
- metering valve
- actuator
- propellant
- excipients
what 6 factors must you consider when formulating a pMDI?
- drug solubility in propellant
- propellant density
- particle size
- valve clogging
- stability
- moisture content
what two key conditions are required for filling pMDI canisters?
- cold (so fill at low temp. drug formulation pre-chilled at -60 degrees)
- high pressure (fill canister at elevated pressure passing the vapour through the valve)
explain how aerosol generation pMDIs work?
- patient presses down on can which opens the channel b/w the metering chamber and atmosphere
- propellants boil in expansion chamber
- propellant droplet form at actuator nozzle ready to disperse at an initial size of 20-30uM and speed of 30m/s.
what pMDI’s are used in the clinic?
- SABA (salbutamol)
- SAMA (ipratropium bromide)
- LABA (salmeterol)
- LAMA (tiotropium)
- ICS (beclometasone, fluticasone)
what are the pros and cons of pMDIs?
pros:
- relatively low cost
- reproducible dose delivered from device
- convenient many doses in one canister
- inert environment protects drug from oxidation and contamination
cons: - patient use errors
- inefficient drug delivery (more drug loss)
what is used to overcome breath-hand co-ordination difficulties when using pMDIs?
- Breath-activated pMDIs (inhaling triggers aerosol activation)
- Inhalation aids (i.e. spacers. This reduces aerosol velocity and allows more time for evaporation of propellant.)
how often do you:
a) wash your spacer?
b) replace your spacer?
a) once a week with warm soapy water and leave to air dry
b) once every 6-12 months
which of the two require more co-ordination, DPI or pMDI?
pMDIs
which of the two depends more on patient’s IFR, DPI or pMDI?
DPI
why do pMDIs have more stability issues than DPIs?
because the pMDI is a 2 phase system whilst DPIs are single phase systems
what are nebulisers?
drugs dissolved/suspended in polar solvents and aerosolised. polar solvent is usually water
how does a nebuliser deliver drug to the lungs?
- drug in solution added to nebuliser drug reservoir
- nebuliser connected to power source
- drug solution aerosolised
- enters the airways as a fine spray of droplets
- deposition independent of IFR
- dissolution
- absorption into lungs
three ways, through which, drugs are delivered, to the lungs, from a nebuliser?
- mouthpiece
- face mask (but not for steroids)
- ventilator
why is the pH of the drug solution buffered ?
to match the pH of the lungs
why are salts added to the drug solution?
to match the tonicity
why are surfactants added to the drug?
to increase solubility
what diluent is included in the nebuliser formulation?
sodium chloride
how do you administer oxygen to COPD patients requiring oxygen and jet nebulisation?
-uses air to administer via a nasal cannula
what is the Bernoulli and Venturi effect?
- compressed gases move through narrow capillary tube
- increased air velocity creates low pressure zone around the nozzle (venture effect)
- fall in pressure causes the formulation to rise from liquid reservoir (Bernoulli effect)
- large droplets impact on baffles ad break into smaller droplets or remain in device.
downside to using a jet nebuliser?
- compressors are quite noisy
2. continuous operation means large proportion of emitted aerosol is released into the air and not inhaled
how do ultrasonic nebulisers work?
- sound waves created from vibration of piezoelectric crystals at high frequency. this requires a power source. no gas flow required.
- this creates crests that break the liquid particles into small droplets to be inhaled
- not suitable for all meds and suspensions though
How does a passive Vibrating Mesh Nebuliser (VMN) work?
- piezoelectric crystal generates vibration from electrical force to transducer horn that’s in contact with the formulation
- vibration creates waves in nebuliser reservoir that travel towards a perforated plate in front of the horn
- aerosols are created when formulation flows through the membrane and drops detach
How does an active VMN work?
- dome-shaped membrane directly connected to vibrating piezoelectric element
- following application of electric current, membrane vibrates up and down causing formulation to extrude through the mesh as droplets
SUMMARY!!
Look at table on side 40!
