D. Colloidal Stability Flashcards
What is an emulsion ?
A liquid-in-liquid colloid
What is a suspension ?
A solid-in-liquid colloid
Why may we have to use dispersed systems ?
- Drug is hydrophobic so cannot be dissolved in water so dissolved in oil and oil is dispersed in isotonic water carrier to dorm an emulsion
- Easier to administer to children
What are the possible emotions ?
W/O/W
O/W/O
True or false?
Dispersion of a liquid in a second immiscible liquid. This created a molecular funk if emulsifier at the interface .
True
What is the purpose of an emulsifier ?
It’s for stability and it is a molecular film that is at the interface of the immiscible liquid particle.
It works by slowing the process of re-separation to the original low energy system.
How are emulsions produced?
They require a large input of energy which is produced by HOMOGENIZATION
What is the most common form of emulsion?
Oil in water
Can re-separation to the original low energy system be prevented ?
No, it can only be slowed down by the emulsifier
How does an emulsifier work ?
The emulsifier positions itself at the interface between the two phases O/W emulsion
The hydrophobic part will position itself in the oil droplet
The hydrophilic part will position itself in the water.
Overall this created a charged layer around the droplet (at the interface)
Repulsion of similar charged prevent droplets from approaching each their and this is what stabilised the emotion and helps slo down re-separation
What a re the applications of emulsions ?
- Intravenous (TPN) for patients who are in intensive care. This can simulate chylomicrons and fats can be absorbed from the GIT
- delivery of hydrophobic drugs
- Oral (enteric feed and oral delivery of hydrophobic drugs)
- Intramuscular (W/O emulsions for sustained release and emulsion vaccine adjuvants)
How would you make a hydrophobic drug into an emulsion ?
Hydrophobic drug will only be soluble in oil.
This is then emulsified
Drug must be very hydrophobic (log p>5)
What could happen if the drug is not very hydrophobic (log p<5) ?
Drug will transfer through the aqueous phase and crystallise out
What can you do to a drug that is insoluble in both oil and water ?
Can solubilise drug in emulsifier solution and then use this to emulsify the oil phase
What is floccuation ?
Particles/droplets cluster together in a open structure.
These particles still maintain their individual identity and can be Reid’s-erased into their single particles/droplets by shaking
What is coagulation or aggregation ?
Small particles aggregate together decreasing the surface area and surface tension is experienced bwtween fewer molecules.
The attraction is very strong
This cannot be redispersed therefore there is a permanent failure of the medicine
What is coalescence/caking ?
Droplet structure is entity list
Impossible for the clinician to redisperse the medicine leading to total failure if the emulsion
What is the kinetic energy of the particles dependant on in dispersed systems ?
Temperature and external forces such as shaking
How big is the diameter of the particles in dispersed systems ?
Less than about 2microns
Are the particles constantly moving in dispersed systems and what is this due to ?
Yes, the particles are constantly moving and this is due to Brownian motion
How may types of forces do the particles in a dispersed system experience. What are they and what are they due to ?
- VR: Energy of electrostatic repulsive interaction
Forces of repulsion due to electrostatic interactions. This is due to forces of attraction due to van der waals forces
- VA energy of attractive interaction due to van der waals forces
Steric interactions but no need to know
What source of charge can the repulsive force be from?
Ion dissolution
Ion adsorption
