Suspension Part 1 Flashcards
Contains undissolved or immiscible drug distributed (dispersed phase) throughout a vehicle (dispersing phase/
dispersion medium)
Dispersion system
Preparations of Dispersion
Liquid or semi solid
Types of dispersion system
Coarse dispersion
Fine dispersion
Colloidal dispersion
Dispersed particles have a greater tendency to separate from the dispersion medium then settles at the bottom.
Coarse dispersion
Particle size of Coarse dispersion
10-50 um
Example of coarse dispersion
Suspensions and Emulsions
Particle size of Fine Dispersion
0.5 to 10 um
Particle size of Colloidal dispersion
1.0nm and 0.5 um
A two-phase system containing insoluble or immiscible drug distributed throughout a vehicle.
Suspensions
2 phases of suspension
Internal and external phase
They are distributed evenly (usually the solid part); contains the active
ingredient
Internal phase aka suspensoid
Usually the liquid part; the vehicle/ solvent
External phase aka suspending phase
Characteristics of a suspension:
murky/cloudy, semi-transparent, usually thick/viscid like syrups but flowy in solutions
Reasons for creating suspensions
- Certain drugs are chemically unstable in solution but stable when suspended
- Ideal dosage forms for patients who have difficulty of swallowing oral solid dosage forms
- Can mask unpleasant taste of drugs because of the decreased contact of the drug that is unpalatable.
- Some drugs are insoluble in all acceptable media
- The liquid character ensures some uniformity of dosage
- More stable than solutions
Features Desired in a Pharmaceutical Suspension
- Suspensoid should settle slowly
- Suspensoid should be readily redispersed
- The particle size of the suspensoid should remain fairly constant
- The suspensoid should pour readily and evenly from its container
- Should be acceptable to the patient
Disadvantage of suspensoid settling down slowly
when it settles down, there will be an increase in the particle’s affinity forming now a hard mass. If this happens, the mass will not break up easily once the drug is shaken and if it will be broken it is in an irregular dose.
settling of the suspended phase
Sedimentation Rate
Stoke’s Equation
was derived for an ideal situation in which uniform, perfectly spherical particles in a very dilute suspension settles without producing turbulence, without colliding with other particles of the suspensoid, and without chemical or physical attraction or affinity for the dispersion medium.
Factors Affecting Sedimentation Rate
1.Dispersion medium
2.Particle size of the suspensoid
3.Density of the suspensoid
4.Solid content
The rate of sedimentation may be appreciably reduced by increasing the viscosity of the dispersion medium
(external phase).
Dispersion medium
The velocity of fall of a suspended particle is greater for larger particles than it is for smaller particles (the smaller the particle size of the suspensiod, the easier the suspension will be poured)
Particle size of the suspensoid
Particle size of the suspensoid
↑ particle size of a suspensoid:
↓ velocity of the suspended particle
The density of the suspended particle should be greater than the density of the dispersion medium
Density of the suspensoid
When density is decreased what happens to the suspensoid?
The suspensoid tends to float
