Dosage forms 2 Flashcards
Disperse system
- One phase (a disperse phase) is distributed throughout a second phase (a continuous phase or dispersant)
- Two immiscible phases in contact
Solutions
- Dissolving a solute into a solvent
- Molecular dispersion
- Contain small particles (ions or molecules)
- Transparent
- Do not separate
- Cannot be filtered
- Do not scatter light
Disperse systems
- One phase (a disperse phase) is distributed throughout a second phase (a continuous phase or dispersant)
Solutions examples
- Saline solution
- Multi-purpose contact lens solutions
- Hydrogen peroxide contact lens solutions
Disperse systems examples
- Droplets of pine oil containing dissolved active germ‐killing ingredient (para‐chloro‐meta‐xylenol or PCMX), held dispersed in water by a layer of surfactant molecules
What are colloids?
- A colloid or colloidal dispersion = a two-phase system of matter; a type of mixture intermediate between homogeneous mixtures and heterogeneous mixtures (size < 1 μm)
- In a phase colloid, small droplets or particles of one substance (the disperse phase) are dispersed in another (the continuous phase)
In a molecular colloid, macromolecules are dispersed in a continuous phase
Properties of colloids:
- Tyndall effect
- Brownian motion
- Adsorption
- Dialysis
- Electrophoresis
- Thixotropy
Tyndall effect
- Colloids scatter light
- Light beam path through colloid is visible due to light scatter
Brownian motion
- Under a microscope, the molecules of the liquid are in motion
- Because of the motion, the larger particles of the colloid are being constantly bombarded by the smaller particles of the liquid
- This motion and bombardment keeps the colloid particles suspended
Adsorption
- A chemical is associated to the surface of a second agent
Often reversible - Can lead to conformational changes
- Manipulate physicochemical properties
- Examples:
Adsorption of gases on solids
Adsorption of surfactants, polymers or proteins
Dialysis
- Separation of suspended colloidal particles from dissolved ions or molecules of small dimensions
- By means of their unequal rates of diffusion through the pores of semi-permeable membranes
Process of Electrophoresis
- Migration of charged particles
- Surface dependent
Thixotropy
Types of colloids
- Gas
- Liquid
- Solid
Based on nature of the interaction between the dispersed phase and the continuous phase:
4. Lyophobic
5. Lyophilic
How to distinguish between a solution and a colloidal dispersion?
Three types of colloids:
- Sol (Gel)
- Foam (Defoamer)
- Emulsion
Lyophobic
Solvent hating (hydrophobic when the solvent is water)
Lyophilic
Solvent liking (hydrophilic when the solvent is water)
Properties of lyophobic
- Inorganic molecules or particles (insoluble)
- Little or no interaction between particles and dispersion medium
- Do not disperse spontaneously, special procedures needed
- No effect on viscosity unsolvated
- Electrolytes: low concentrations may stabilise,
higher concentration causes instability
Example of lyophobic colloids
Calcium phosphate
Lyophilic
- Large organic molecules in colloidal size range
Solvated by medium (H2O – this is hydrated) - Disperse spontaneously
- Increase viscosity, forming gels at higher concentrations
- Electrolytes: generally stable but “salted out” by very high concentrations due to desolvation
Examples of Lyophilic colloids
- Starch
- Gelatin
Particles in colloids, how big?
Less than 1 um (micrometer)
Colloids - Sol
a colloidal suspension of small solid particles in a continuous liquid medium
Colloids - Gel
- a colloidal suspension in which the liquid medium has become viscous enough to behave more or less as a solid
- Solid particles will arrange themselves into a 3D structure within the liquid solvent, giving the solution a rigid, definite shape as in a jelly
Examples of Gels
- Nail polish
- Styling gel
- Eye gel
Examples of PHARMACEUTICAL Gels
- Aloe Vera gel
- ‘Burncare’ - relieve burn gel
- Ibuprofen Gel
Gels: what phase?
- Lyophobic - two-phase system
- Lyophilic - one-phase system
Lyophobic - two-phase system
a) Flocculated particles in a two-phase gel structure
b) Network of elongated particles or rods forming a gel structure
Lyophilic - one-phase system
c) Matted fibres as found in soap gels
d) Crystalline and amorphous regions in a gel of carboxymethylcellulose
Gels formulation:
Gelling agents:
-natural gums (tragacanth, carrageen, pectin, agar, alginic acid)
-Semisynthetic material
-synthetic
Humectants; prevent drying out (glycerol, sorbitol)
-preservatives
-water
Whats are foams?
Gases dispersed in a liquid/solid
- formed by trapping many gas bubbled
What are foams normally used for?
Delivery of enemas and topical drugs
Why are foams sometimes troublesome in manufacture?
Produced as UNWANTED by-products
(if foam forms on shaking)
What instructions/directions are common when using foams?
Shake well before use
Defoamers/ antifoaming agents:
Foam breakers and preventers
- Act as small droplets forming in the foam lamellae
- Displaces surfactants (which stabilise the thin films) at the air-water interface
Example of a defoamer
Silicone fluids
Emulsions
A ‘pseudo-stable’ dispersion of at least two immiscible liquids, one of which is dispersed throughout the other in the form of fine droplets (generally oil and water) stabilised by the presence of an emulsifying agent (known as emulsifier
Suspensions (not a colloid)
Course dispersion in which insoluble particles, generally > 1 μm, are dispersed within a liquid medium which is usually aqueous
Directions to use suspensions
- Settle out
- Shake to stay suspended
solution v colloid v suspension
Consider properties:
1. particle size
2. appearance
3. separation
4. filtration
5. effect of light
6. visibility
Sizes
Solution : less than 10^-9
Colloid : less than 10^-6
Suspension : more than 10^-6
