Problem 1 Flashcards
Stokes’ law
Describes Particle sedimentation
v = 2r^2g(Ps-P1) / 9n
v in stokes’ law
Sedimentation velocity
g in stokes’ law
Acceleration due to gravity
r in stokes’ law
Particle radius
Ps in stokes’ law
Solid density
P1 in stokes’ law
Liquid density
n in stokes’ law
Liquid viscosity
Methods to reduce sedimentation rate
Reduce particle size
Match liquid density to that of solid
Use viscous liquid
Add thickener
Problem with suspensions
Particles fall due to gravity + could result in under/over dosing of patient
The smaller the particle…
The longer the particle settles/sediment to the bottom of bottle
Disperse systems
Contain 2phases
Why is amoxicillin sodium (salt) used in injection formulations
Hydrolysis is not a problem
Use of the salt allows rapid dissolution to form IV injection
Amoxicillin sodium paediatric formulation
Oral liquid formulation is stale for at least 7 days
- if drug is hydrolysed then the active drug concentration falls below MIC + treament fails
- risk of accelerating onset of resistance
- no stable liquid formulation is not possible with amoxicillin sodium
Surfaces
Boundary of a material
- in vacuum properties of surface is determined by material
Surface tension
Uneven distribution of forces leads to a net inward force that drives the molecules to decrease the surface area of the system.
- minimises free energy
- thats why drops of liquids are spheres - minimal surface area
