Page 275 - Pharmaceutics IV (02-06-01305)
P. 275
3/30/24
Particle size, shape and density as
Formulation factors
Generally, particles in the size range of 1–5 μm are considered respirable
(have significant lung deposition).
• The smaller particle size drug migrates to the lung alveoli, whereas the larger particle size
excipient deposits in the back of the throat and in the major respiratory airways.
• Particle shape and density determine the proportion of inhaled particles that deposit in deep lung
alveoli versus major airways.
Thus, optimized performance of both the device and the formulation is
critical to ensuring high and consistent lung deposition. (spacer!!)
Most of the therapeutic dry powders for DPIs are currently made with
particles of small aerodynamic particle diameter (e.g., 90% particles below 5
μm) and density of 1 ± 0.5 g/cm3.
Prof Alyaa Ramadan, ceutics, AU
57
What is aerodynamic diameter?
aerodynamic diameter, dA, is defined as the
diameter of spheres of unit density, which
undergo the same acceleration in the air stream
as non-spherical particles of arbitrary density,
therefore moving along the same streamlines.
Prof Alyaa Ramadan, ceutics, AU
58
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