Inhalable therapeutic aerosols Flashcards
What is an aerosol?
A relatively stable suspension of solid or liquid particles in a gaseous medium
What do aerosol aerodynamic properties depend on?
size, shape and density
What 3 shapes do aerosols come in?
Spherical
Fibrous
Aggregates
What is the definition of pharmaceutical aerosols?
Colloidal systems of very finely subdivided liquid or solid pharmaceutical active particles dispersed in and surrounded by a gas
What 6 factors control drug delivery to the lung?
Formulation Device Patient activation Lung deposition Dissolution Absorption
The majority of harmful particles are what size?
3 microns or less
What is the main extrinsic cause of asthma?
House-dust mite faeces
What are the advantages of using inhalation therapy for local delivery?
Drug delivered directly to site of action
Drug action onset is rapid
Less drug in systemic circulation
Lower doses required
What are the advantages of inhalation therapy for systemic delivery?
Extensive blood supply gives potential for rapid absorption into systemic circulation
Avoids first pass metabolism
Increased bioavailability
What size particles deposit in alveoli?
0.5-2 microns
What size particles deposit in the bronchus?
2-7microns
What size particles deposit in the trachea?
7-10microns
What 3 factors control aerosol deposition?
Aerosol properties
Mode of inhalation
Patient relating factors
Impaction occurs for particles of what size?
> 10microns
Sedimintation occurs for particles of what size?
2-3microns
Diffusion occurs for particles of what size?
<1micron
What is inertial impaction?
Impaction caused by the tendency of particles to continue to move in a straight line
Inertial impaction perdominately occurs for what?
Large particles when the gas airstream is fast, changing direction or turbulent
Where does inertial impaction mainly occur?
Oropharynx, larynx or at bifurcations
What is gravitational sedimentation dependent on?
Terminal settling velocity of particle
When does gravitational sedimentation occur?
Where air velocity in respiratory tract is low and residence time is high
What is diffusion (Brownian motion)?
Particles bombarded by air molecules giving rise to a ‘random walk’
When is difffusion dominant?
As particle size approaches the mean free path of the air molecules
What can improve diffusion deposition efficiency?
High residence time (Breath holding)
What is interception?
Deposition where particles contact walls
What is electrostatic deposition?
Charge particles repel-increase in migration towards airway walls
The world market for asthma drugs is expected to exceed what by 2015?
$25 billion
What are the 3 main types of inhalable devices?
pMDI
DPI
Nebuliser
What is the aim of nebulisers?
Reproducibly deliver correct dose to site of action with minumum waste
Many nebulisers deliver as little as what of the target dose?
10%
What was the dominant nebuliser system on the market pre 2000?
Pneumatic nebulisers
What are the 4 componenets of pneumatic nebulisers?
Disposable unit
Compressor
Interfaces
Valves/holding chamber
What are the pros and cons of pneumatic nebulisers?
Cheap Small particle sizes Variable performance Dead volume Lower output Portability
What are the components of high frequency ultrasonic nebulisers?
Electronic power source Liquid reservoir Synthetic piezoelectric ceramic disc Air fan Mouthpiece
What are the pros and cons of ultrasonic nebulisers?
Reproducible Small particle size High output Small and quiet Low aerosol inertia Size increase at end of life Expensive Heats solution to 40degC Poor for suspensions
