Pulmonary Drug Delivery [Vitaliy] Flashcards
What is pulmonary drug delivery?
Drug is delivered to the lungs to be absorbed into the blood circuulation
What occurs in the lungs?
The lung is an organ of external respiration
Oxygen and carbon dioxide are exchanged between blood and inhaled air
Why are the lungs an attractive drug target?
Large surface area
Good blood supply
What is the aerodynamic particle diameter (da)
The diameter of a sphere with a density of 1 g/cm3 that has the same aerodynamic behaviour as the particle which shall be characterised
List the 3 processes responsible for particulate deposition in the lungs
- Impaction
- Gravitational sedimentation
- Diffusion
Different particles will deposit differently in the lungs
What is gravitational sedimentation?
Particles settling under gravity will attain a constant terminal settling velocity, Vt
Gravitational sedimentation of an inhaled particle is dependent on its size, density and residence time in the airways
What is inertial impaction?
This is the dominant deposition mechanism for particles > 1um in the upper tracheobronchial regions
A particle with a large momentum may be unable to follow the changing direction of the inspired air as it passes the bifurcations - so it will collide with the airway walls
What is brownian diffusion?
Of little significance for particles > 1um
Particles below this size are displaced by a random bombardment of gas molecules = particle collision in the airways
The probability of particle deposition by diffusion increases as the particle size decreases
How are larger particles (greater then 10um) deposited in the airways?
The particles will impact in the upper airways
They are rapidly removed by coughing, swallowing and mucociliary processes
How are smaller particles (0.5-5um) deposited in the airways?
The particles may escape impaction in the upper airways and will deposit by impaction and sedimentation in the lower airways
Describe the structure of the airways
Trachea > Mainstream bronchus > Lobar bronchus > (Segmental bronchus) > Bronchiole > Aveolar duct > Aveolus
List the 4 physical factors which affect particle deposition in the airways
- Lung morphology = drug particles must pass down a successive series of branching tubes of constantly decreasing size
- Oral vs nasal breathing = for pulmonary, aerosols are inhaled via the mouth
- Inspiratory rate flow = increasing inspiratory rate flow will enhance deposition by impaction in the larger airways
- Breath holding = enhances the deposition of particles by sedimentation and diffusion
How does optimal aerosol deposition occur?
With slow, deep inhalations to total lung capacity
Followed by breath-holding prior to exhalation
List 5 pharmaceutical factors affecting aerosol deposition
- Aerosol velocity
- Size and size distribution
- Shape
- Density
- Physical stability
Describe the journey of the drug particles through the mucus barrier
The drug needs to dissolve in the mucus layer
Once in solution, the drug will then diffuse through the mucus layer and enter the aqueous environment of the epithelial lining liquid