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Ceutics II - Exam 5 (Awasthi)
Terms in this set (29)
Reducing dosing frequency
Enhancing patient compliance
Minimizing untoward effects
Being intelligent and responsive
Goals of liposomes in drug delivery
Therapeutic (doxorubicin & Amphotericin)
Liposomes available in commerce
Created by a mixture of phospholipids and cholesterol when hydrated with aqueous solutions (spontaneous)
-Closed - spherical vesicles with aqueous center
-Arranged in concentric bilayer membranes
-Can carry water soluble/lipid soluble drugs
Characteristics of liposomes
Polar phosphate "head"
Non polar "tail"
A phospholipid consists of?
What are the non-polar tails made of?
The longer the fatty acid tail of a liposome is the ---- it will be
Prone to oxidation
Stabilized by Vitamin E & Anti-oxidants
Phospholipids/liposomes are prone to what type of reaction?
What can stabilize this?
-Imparts rigidity to the lipid layer
-added in equal amounts to phospholipids
Characteristics of cholesterol in liposomes
-Passive loading (drug is incorporated into water phase when making liposomes)
-Active loading aka remote loading (Drug is loaded after the liposome is formed)
Ways to load a drug into a liposome
Passive loading wastes alot of drug... The liposomes can only hold a small amount of water - so the rest of the drug will be in the external phase, which has to be discarded
Which loading method is more efficient?
A gradient difference between the inside and outside of the liposome
(typically w ammonium or H+ ions)
What is the basic mechanism used in active loading of drugs into liposomes?
The drugs will keep moving inside the liposome and go from a neutral charge to a positive charge - This charge keeps the drug from moving back out of the liposome
How does the liposome retain the drug inside ?
Lamellarity (how many layers of lipids)
amount of drug loaded per liposome
presence of surface coating
Characteristics of liposomes
Multilamellar vesicles (multiple layers)
Unilamellar vesicles (single bilayer)
Two lamellarities of liposomes
Unilamellar (more efficient in drug encapsulation)
Multilamellar - more lipid will be consumed, which will waste expensive phospholipids
Which lamellarity method is more efficient?
-Range = 80-300 nm
-Reduction achieved by: High shear homogenization or extrusion through pores
-^^can do this multiple times to narrow the size
Characteristics of liposome size
Most liposomes used in clinical practice have what kind of charge?
What charge (+/-) will be less toxic because they have less activity to act with the cell membranes?
They would aggregate and form much bigger particles
What is the negative significance of having neutrally charged liposomes?
-Increase in size upon storage
-Breakdown: loss of structural integrity due to enzymatic of chemical degredation, incompatibility within the formulation, or storage conditions
-Leakage of drugs
What things tend to interfere with the stability of liposomes?
The macrophages present in these organs take up the liposomes and try to metabolize them
Liposomes accumulate in organs of monocytes phagocyte systems such as?
PEG chains are added to the surface of the liposomes to prevent them from accumulating in the RES (liver, spleen, bone marrow) - this will keep them in circulation for a longer period of time (Increase their half-life)
What is the significance of Stealth (long-circulating) liposomes?
How are liposomes administered to a patient?
-10-15 K moles/liposome
-Plasma half-life 2/3 days
-Coated on the outside with a PEG lipid
-Must be compounded
Comes in a 3 vial system
(Doxorubicin, liposomes, buffer)
-Amphotericin B liposomes
-Antifungal is in the
-Prolonged retention of small drugs in the body
-Altered PK of encapsulated drug
-Enhanced drug stability
-IV prep of difficult to admin drug
Benefits of liposome encapsulation confer
Where does most of the liposome therapy occur?
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