PH2107 - Solutions 3 Flashcards
What can be used to enhance solubility using excipients that create disperse systems?
- surfactants
- emulsions
- vesicles / nanoparticles
- chelators / complexants
What is a surfactant?
An amphiphilic organic compound comprised of hydrophobic groups (tails) and hydrophilic groups (heads)
Give some examples of surfactants
- octanol (long chain alcohol, non-ionic)
- sodium dodecyl sulphate (anionic)
- benzalkonium chloride (cationic)
- cocamidopropyl betaine (zwitterionic)
Give examples of amphiphilic biological compounds?
- phospholipids
- cholesterol
- glycolipids
- fatty acids
- saponins
What is solubilisation?
Solubility can be improved by addition of a surface active agent (micellar solubilisation)
What properties must a surfactant have used for solubilisation?
- non-toxic
- non-irritant
- miscible with the solvent system
- compatible with the other ingredients
What effect do surfactants have?
Surfactants lower the surface tension of a liquid, the interfacial tension between two liquids or that between a liquid and a solid
What do surfactants act as?
- detergents
- wetting agents
- emulsifiers
- foaming agents
- dispersants
How do surfactant molecules migrate?
Surfactant molecules will migrate to the water surface, where the insoluble hydrophobic group may extend out of the bulk water phase, either into the air or, if water is mixed with an oil, into the oil phase, while the water soluble head group remains in the water phase
What is an emulsion?
A dispersed system comprised of two or more immiscible liquids
- oily
- aqueous
What are the two phases that make up an emulsion?
Disperse phase
Continuous phase
What state are emulsions in?
Emulsions may be semi solids or liquids
What determines the state of an emulsion?
The oil and water proportions
Route of administration
How is an emulsion formed?
High energy input needed as they are thermodynamically incompatible
What can be added to an emulsion to increase kinetic stability?
An emulsifier (emulgent)
What is propofol?
A short-acting medication that results in a decreased level of consciousness and lack of memory for events. Its uses include the starting and maintenance of general anaesthesia, sedation for mechanically ventilated adults and procedural sedationWhat are microemulsions typically used for?
What are microemulsions typically used for?
To kill microbes (bacteria, viruses), blood and sperm
How much force is needed to make a microemulsion?
The smaller the droplet, the greater the surface tension and thus the greater the force to merge with other lipids
How is a microemulsion made?
The oil is emulsified with a high shear mixer with detergents to stabilise the emulsion, so when they encounter lipids in the membrane or envelope of bacteria/viruses, they force the lipids to merge with themselves, disintegrating pathogen membrane
What is a vesicle?
A supramolecular assembly of lipid molecules in an aqueous environment
What is a bilayer?
A fundamental structural feature of a biological membrane
What is a micelle?
A spherical aggregate, ~150nm of surfactant molecules dispersed in a liquid colloid
What is a normal phase micelle?
A micelle with the headgroups facing away from the centre (oil-in-water micelle)
What is an inverse micelle?
A micelle with the headgroups at the centre with the tails extending out (water-in-oil micelle)
How are micelles useful in pharmacology?
Insoluble species can be incorporated into the micelle core, which is itself solubilised in the bulk solvent by virtue of the head groups’ favourable interactions with solvent species
