Oral powders Flashcards
why can you not just have drugs in the powder form?
usually too sticky as a powder so needs to mix with something else to make it a working tablet
what does “powder” mean in pharmaceutics ?
As a dosage form:
“describes a formulation in which a drug powder has been mixed with other powdered excipients to produce the final product”
As a precursor of a dosage form:
Can be precursor of tablets either
- directly (compressed to form tablets)
- or indirectly (via granules)
What does granules mean in pharmaceutics?
As a dosage form:
“granules as dosage forms are powder particles that have been aggregated to form a larger particle 2 to 4 mm diameter”
As a precursor of a dosage form:
Granules can also be an intermediate of tablet manufacturing
What are advantages of powders/granules vs tablets/capsules/liquids?
- more stable in liquid
- convenient for large doses
- faster dissolution rate that capsule or tablet (material is already in powdered form - small particle sizes dissolve faster)
what are disadvantages of powders/granules vs tablets/capsule/liquids?
- less convenient to carry than tablets/capsules
-difficult to mask (unpleasant taste) - not suitable for administration of potent drugs
- not suitable for drugs inactivated in the stomach or that can cause stomach irritation
what are uses for powders and granules for pharmaceutical use orally?
- bulk powders or granules for internal use
- divided powders or granules (single preparations)
what are other administration routes for powders and granules?
- dusting powders for external use
- insufflation (ear/nose/throat)
- antibiotic syrups to be reconstituted before use
- powders to be reconstituted into injections
- dry powder inhalers
why is particle size so important ?
- Drug bioavailability
- settling rate (suspensions)
- possibility of obtaining homogenous mixtures
- flowability
- tolerability of some dosage forms
what are the 4 different types of particle size distribution?
- Monosized distribution (very unlikely)
- normal distribution
- positively skewed distribution
- bimodal distribution
how do you get the cumulative frequency of particles?
Equivalent particle diameter + percentage
what are forces that favour the affect of powder flow?
Gravity (causes it to flow down)
True density of particles
Angle of surface over which particles are flowing
what are the forces that are against powder flow?
Adhesion forces (particle and container) - might stick to walls
Cohesion forces (particles may become attached to each other )
how does fine powders effect powder flow?
they have higher surface/mass ratio and therefore higher cohesion
what shape particles flow easier?
spherical
How can you measure flowability
Angle of repose
Powder is put through a funnel to form a cone shape
Want a low angle of repose for powder flow (non-cohesive)
What is the bulk/apparent volume?
The volume occupied by a powder including the pores (ie. empty gaps between particles)
What is the tapped volume?
volume occupied by a powder after tapping (tapped density test uses a powder in a measuring cylinder and machine is used to tap powder through to get weight and volume)
what is the true volume?
The volume occupied by a powder excluding the volume occupied by the pores
how do you calculate the bulk density?
Bulk density = mass/Vbulk
how do you calculate the true density?
True density = mass / Vtrue
What value is always less bulk density or true density?
bulk density
how do you calculated the porosity?
1 - volume (particles) / volume of (bulk)
what is porosity and why is it important?
- important not only in powders but tablets too
- measure of spaces between particles
what does a high porosity mean?
water is able to move into the tablet more quickly to be dissolved quicker
what is granulation?
the process in which homogenous mixtures of primary powder particles form larger, still homogeneous particles called granules (process of mixing powders)
what are advantages of granulation?
1) improve powder flow
2) prevent segregation
3) improve compaction
Reduced generation of dust
Granules occupy less volume
what is wet granulation?
Powders are mixed through with a granulating sieve and the mass is forced through a sieve
- popular with tablets that contain large amounts of drugs in it eg. paracetamol
what is the wet granulation mechanism?
1) Adhesion and cohesion forces in immobile films
2) interfacial forces in mobile liquid films
3) solid bridges (hardening binders or crytallisation of dissolved substances)
4) attractive forces between particles
what is the granulation mechanisms of dry granulation?
Attractive forces between solid particles
- solid bridges (by partial melting)
what is the mechanism of dry granule formation?
- applied pressure
- formation of a sheet
- milling and sieving
- granules
