Liposomes Flashcards
(50 cards)
What is the size of small unilamellar vesicles (SUVs)
20 - 100nm
What is the size of large unilamellar vesicles (LUVs)
> 100nm
What is the size of giant unilamellar vesicles (GUVs)
> 1000nm
What is the size of oligolamellar vesicles (OLVs)
100 - 1000nm
What is the size of multilamellar vesicles (MLVs)
> 500nm
What lecithins could you use for lipids in liposome formulation?
- Egg yolk, soybean
- Derivatives of glycerol
- Not a single compound - mix
What phospholipids could you use for lipids in liposome formulation?
Phosphatidylcholine
Phosphatidylethanolamine
Phosphatidylglycerol
Phosphatidylserine
What does Tc depend on?
Lipid composition
Anions/cations present
What is Tc of phospholipids?
Tc is phase transition temperature
Phospholipids in a bilayer undergo a temperature dependent phase transition from a gel (lower temps) to a more fluid state (higher temps)
During phase transition, fatty chains expand and permeability increases
Tc close to ambient or body temp - very leaky PLs
At body temp, a fluid state will make the liposomes leaky and the encapsulated drugs are likely to escape before reaching the site of action
How could you formulate a liposome to control liposome vesicle permeability
Use at least 2PL with different Tc values
Choose phospholipids with gel states at physiological conditions
Use cholesterol to fill in the gaps between adjacent PL chains
What is the critical packing parameter of amphiphile shape which will form vesicles
0.5 - 1
What would you add to make a liposome negatively charged?
Oleic acid
What would you add to make a liposome positively charged?
DOTAP
Where are drugs with a log p ~1.7 stored?
These are aqueous soluble drugs which are stored in central aqueous compartments and compartments between bilayers
Drugs with intermediate logP (between this and 5) present greater challenges for incorporation
Where are drugs with a log p > 5 stored?
These are lipid soluble drugs
They are stored within the membrane bilayer +/- interacting with bilayer surface
Drugs with intermediate logP (between this and 1.7) present greater challenges for incorporation
Give 3 examples of liposomal systems where the drug was loaded using active loading
Caelyx/Doxil - doxorubicin HCl is loaded using ammonium sulfate derived chemical potential gradient
Myocet - loading of doxorubicin using citric acid derived chemical potential gradient
DaunoXome - daunorubicin loaded using citric acid derived chemical potential gradient
What size filter should liposomes be prepared with?
200nm membrane filter
What is the problem with steam sterilisation of liposomes?
Heat may result in gel-fluid phase transition and hydrolysis
What is the problem with chemical sterilisation of liposomes?
It uses ethylene oxide - how is this removed post sterilisation?
When is gamma irradiation especially suitable?
When lyophilised
How would particle size be measured in QC?
DLS - dynamic light scattering
SEC - size exclusion chromatography
NMR - nuclear magnetic resonance
TEM - transmission electron microscopy
Cryo-TEM - cryogenic TEM
AFM - atomic force microscopy
What is zeta potential?
Measures charge and provides important information on aggregation and membrane interaction
What is encapsulation efficiency measured?
Remove unencapsulated drug
Use organic solvent to remove entrapped drug and quantify it using UV/HPLC analysis
What material would you use if you wanted to make a pH sensitive liposome?
DOPE - dieoleoylphosphatidylethanolamine
