MDM: SDF DS Flashcards
- Explain the difference between a drug and a medicine.
A medicine is the drug along with additional excipients which help turn the drug into a medicinal formulation in which the patient is able to take.
The drug is the active substance which has an effect on the body.
- Explain the difference between hydrogen bonds and van der Waals forces in relation to solid particles.
Van der waals forces are fairly weak in contrast with hydrogen bonds which are much stronger. These can occur between H and O, N, F
- State the Noyes-Whitney equation and briefly describe how particle size affects the dissolution of a drug substance.
Dc/dt = DA(C-Cs)/ h
The smaller the particle the greater the dissolution as the greater the surface are so are of the particle in contact with the GI fluid
- Briefly describe what the term ‘equivalent diameter’ means when referring to the measurement of particle size.
It is a method to define size of a particle using one number. It is a hypothetical sphere which represents an approximation to the true size and shape of the particle
What are 6 types of equivalent spheres and what they are equivelent too
- Free falling diameter - the diameter of a sphere which has the same density and free faling speed as the particle in a fluid with the same density and viscosity
- Surface diameter - the diameter of a sphere which has the same external surface area as the particle
- volume diameter - the diameter of a sphere which has the same volume as the particle
- projected are diameter - the diameter of a spheres which has the same area as the projected area of the particle resting in a stable position
- sieve diameter - the width of the minium square apeture which the particle will pass through
- surface volume diameter - the diameter of a sphere which has the same external SA to volume ratio as the particle
- Briefly describe the following methods of particle size analysis:
- Sieve analysis
- microscopic analysis
- electrical stream sensing
- laser diffraction
- photon correlation spectroscopy
- sedimentation methods
- Sieve analysis: Powder placed on top of stack of agitated sieves. Particles smaller than the aperture of the sieve will move down to the next mesh. This process continues until all particles are on the correct mesh and are too big to move any further
- Microscopic analysis:
Light microscopy: Particles put on a microscope slide and analysed using a microscope. Gives a 2-dimetional image of the particle.
SEM/ TEM: Used for much smaller particles and gives a 3-dimensional image of particle
- Electrical stream sensing: Particle suspension is drawn through an orfice accurately drilled into a sapphire crystal set into the wall of a hollow glass tube. Measuring particle size by change in electrical signal generated from the particle passing through the orifice
- Laser light-scattering: Monochromatic light shown at particles causing light to be scattered. The angle of scattering corresponds to the size of particle. Scattered light focused onto a photodetector by a lens. Electrical current is processed into size distribution data.
- Photon-correlation spectroscopy: The intensity of scattered light at a given angle is measured as a function of time for a population of particles
- Sedimentation methods: Using stokes and Reynolds number to determine particle size by the
- There are various factors which influence our ability to particle size reduce a powder. Briefly describe how the following factors affect this:
a. The toughness of a material.
a. Its surface hardness;
a. The type of material (plastic, elastic or brittle).
A. Brittle materials- strained leads to crack propagation
Tough materials (plastic flow) – allow strained energy without crack propagation
b. Hard materials- more difficult to communitae and lead to abrasive ware of metal mill parts therefore contamination
Soft materials (with elastic component) - Soft but difficult to size reduce. Absorb large amounts of energy without crack propagation/ initiation. They resist comminution at ambient (room temp) or elevated temperatures and can be more easily reduces when temperatures are lowered below the glass transition point of the material. At these temperatures the material changes from plastic to britial behaviour and crack propagation can be facilitates
·c. Plastic – cutter mill (shear/ cutting force needed)
Elastic – Cutter mill (elastic/ plastic deformation)
· Brittle – runner mill needed
- State the various ways in which energy is lost from a particle size reduction process, other than that causing a reduction in size.
- · Elastic deformation of particle
- · Plastic deformation of particle without fracture
- · Deformation to initiate cracks without fracture
- · Deformation of metal machine parts
- · Interparticulate fracture
- · Heat
- · Sound
- · vibration
- Briefly describe how the following mills achieve particle size reduction and indicate what type of material each one may be suitable for:
a. Cutter mill.
- Elastic/ plastic materials
- To size reduce dry granules prior to drying
- Set of rotating knives on a horizontal rotator and set of stationary knifes attached to mill casing. Particles fractured between the 2 sets of knives
- Briefly describe how the following mills achieve particle size reduction and indicate what type of material each one may be suitable for:
b. Hammer mill.
- · Size reduction by impact
- · Produce powders of narrow size distriubtion
- · Hammers swing out radially from rotating central shaft fracturing the particles. Particles maintain in screen until small enough to pass through aperture.
- Briefly describe how the following mills achieve particle size reduction and indicate what type of material each one may be suitable for:
c. a. Vibration mill.
- · Impact size reduction
- · During milling the whole body of the mill is vibrated and particle size reduction occurs as a result of repeated impact
Briefly describe how the following mills achieve particle size reduction and indicate what type of material each one may be suitable for:
e. ball mill
- Combined impact and attrition size reduction method
- Particles in ball which is rotated on its horizontal longitudinal axis
- Important factors: amount of particles:
- too much cushioning effect, too little – not effective and abrasive ware too mill parts
- speed
- Briefly describe how the following mills achieve particle size reduction and indicate what type of material each one may be suitable for:
e. FLuid energy mill
- Impaction and attrition combined method
- Fluid injected as as a high pressure jet through nozzle at bottom of loop. High pressure velocity of air gives rise to turbulence zone with high kinetic energy. Causes particles to impact with each ither anf racture
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Why is size reduction required?
- To produce particles of adequate size for certain routes of administration e.g. inhalation methods
- Optimise dissolution rate
- Improve aesthetics and stability
- improved production efficiency
- breakdown of cells to allow extraction of APIs from plants
- Provide appropriate size for drug targeting (respiratory med)
Describe sieving size seperation methods
- · Agitation methods: Mechanically induced vibration of sieve meshes
- Brushing methods: Brush used to reorientate particles on surface of sieve and prevent apertures becoming blocked. Brush shouldn’t force particles through apeture
- Centrifugal:
