Aerosols Flashcards
Three advantages of using aerosols for drug delivery.
*non-invasive
*rapid onset of action
*lungs provide-large surface area and readily accessible blood supply
What is an aerosol?
Any system of solid or liquid particles of sufficiently small diameter to maintain some stability as a suspension in air
What 3 factors affect aerosol deposition?
*physical properties of aerosol particle
*ventilation factors
*airway anatomy/lung mechanics
What are the benefits of using smaller drug particles in aerosols?
*greater total lung deposition
*farther distal penetration
*more peripheral lung deposition
What is the definition of aerodynamic diameter?
The diameter of a unit density sphere with the same settling velocity as the particle in question. Used to predict where in respiratory tract aerosol particles deposit.
What is the aerodynamic diameter equation and what does each component mean ?
dpa=dps x square root (pp)
Dpa= aerodynamic diameter
Dps= stokes diameter of particle
Pp= particle density
What is mass median diameter (MMD or Xg)?
Particle diameter that divides frequency distribution of particle in half
*50% of aerosol mass has particles with large diameter
*50% of aerosol mass has particles with smaller diameter
What is the MMAD?
Mass median aerodynamic diameter - aerodynamic diameter around which the mass is centred (shape and density accounted for). Describes deposition of particles in respiratory tract.
What are the 4 mechanisms of deposition?
*Inertial impaction
*gravitational sedimentation
*brownian diffusion
*electrostatic precipitation
What is inertial impaction?
Refers to particles that tend to continue in their present trajectory rather than follow the curvature of the airways. They impact the airway wall. To impact the surface, particles must have enough inertial momentum to overcome drag force of gas flow on the particles.
What is gravitational sedimentation?
Smaller particles (<2um) that are able to follow the airstream and penetrate the more peripheral bronchioles and alveoli. It is enhanced by breath-holding or slow steady breathing.
What is brownian diffusion?
Small particles (<0.5um) are displaced by random bombardment of gas molecules and collide with airway walls. Particles deposit in distal lung.
What is electrostatic precipitation?
The charge on an aerosol which can enhance the deposition of very small aerosols that have high mobility. Cause problems with spacers (plastic).
What do ventilation factors consist of?
*particle velocity
*inspiratory flow- fast =increased upper airway deposition via inertial impaction. Slower=distal deposition via gravitational sedimentation.
*inspired volume= size of inspired vol affects amount of aerosol entering lungs+depth of penetration.
*breath-hold duration= enhance deposition by grav. sedimentation
*timing of aerosol delivery during inspiration
Advantages of aerosol delivery?
*low doses of aerosolised drug can be delivered directly to site of action locally within airways
*drugs can be delivered to systemic circulation via distal lung leading to rapid absorption (anaesthesia)
Advantages and disadvantages of MDI?
Advantages
*convenient
*less expensive than neb
*hard to contaminate
*portable
Disadvantages
*patient needs to have correct actuation
*difficult to deliver high doses
What if cfc?
Chlorofluorocarbons. Non cfc propellants include hydrofluoroalkane-134a. First non cfc pMDI was salbutamol
Advantages and disadvantages of spacers?
Advantages
*less patient coordination needed
*less pharyngeal deposition
Disadvantages
*more complex for some patients
*more expensive than MDI alone
*less portable
When is it important to use a spacer with pMDI?
*children
*steroids-less irritation and infections
Advantages and disadvantages and jet/ultrasonic nebulisers?
Advantages
*patient coordination not required
*high doses
*no cfc released
Disadvantages
*expensive
*not portable
*contamination possible
*needs prepared
Advantages and disadvantages of DPI’s?
Advantages
*less patient coordination
*breath hold not needed
*no propellant needed
Disadvantages
*needs moderate to high inspiratory flow
*hard to deliver high doses
*high pharyngeal deposition
What are the 4 types of DPI’s?
*disposable single unit dose- directhaler
*reusable single unit dose-spinhaler
*multi unit dose- diskus
*multi dose (reservoir)-turbohaler
How are deposited aerosols cleared?
*absorbed into blood stream
*local inactivation through macrophage ingestion-slow
*lymphatic clearance-drug absorbed into lung tissue and cleared through lymphatic drainage
*mucocillary transport
What is deep lung delivery?
Alternative to injection. Enables delivery of larger macromolecules not suitable for oral or transdermal delivery i.e insulin for diabetes. Reduces cost, increases patient compliance.
Disadvantages/challenges of deep lung delivery?
*Barrier- ciliated mucus covered cells of airways.
*Have to deliver mg/dose not ug/dose
*most macromolecules more stable as solids than liquids
