3. Liposomes are concentric bilayered vesicles in which an
aqueous volume is entirely enclosed by a membranous
lipid bilayer mainly composed of natural or synthetic
phospholipids.
6. The main components of liposomes are :-
1. Phospholipids
2. Cholesterol
Classification of phospholipids
Natural: (e.g. Phosphatidyl choline, Phosphatidyl ethanolamine,
Phosphatidyl linositol etc )
Modified: (To reduce unsaturation, e.g. Hydrogenated
phosphatidyl choline )
Semisynthetic: (e.g. Dipalmitoyl phosphatidyl glycerol)
Synthetic : (e.g. Dioleoyl phosphatidyl choline, Dioleoyl
phosphatidyl ethanolamine )
Phospholipids with non-natural(Head) groups:
PEG chains attached to phosphatidyl ethanolamine
7.
8.
9.
10. Cholesterol
is added to form bilayer structure by incorporating it into the
phospholipid membrane in very high concentration up to 1:1 or
2:1 (cholesterol:phopholipid).
It fills in empty spaces among the phospholipid molecules.
It acts as fluidity buffer, i.e. decreases fluidity or microviscosity of
bilayer.
After intercalation with phospholipid molecules alter the freedom
of motion of carbon molecules in the acyl chain.
It reduces the permeability of the membrane to water soluble
molecules.
It stabilizes the membrane in the presence of biological fluids such
as plasma.( This effect used in formulation of i.v. liposomes)
Charge molecule:
Sometimes liposomes induced with a charge to improve
their absorption.
Diacyl glycerol, stearyl amine and diacetyl phosphate have
been incorporated in the liposomes so as to impart either a
positive or negative charge to these structures.
18.
Provide controlled drug delivery
Biodegradable, biocompatible, flexible
Non ionic
Can carry both water and lipid soluble drugs
Drugs can be stabilized from oxidation
Improve protein stabilization
Provide sustained release
Targeted drug delivery or site specific drug delivery (Flexibility to couple
with site specific ligands to achieve active targetting)
Stabilization of entrapped drug from hostile environment
Alter pharmacokinetics and pharmacodynamics of drugs (reduced
elimination increased circulation life times)
Can be administered through various routes
Can incorporate micro and macro molecules
Act as reservoir of drugs
Therapeutic index of drugs is increased
Site avoidance effect (avoids non-target tissues).
Can modulate the distribution of drug
Reduction in toxicity of the encapsulated agent.
19.
Less stability
Short half life
High production cost
Quick uptake by cells of R.E.S
Allergic reactions may occur to liposomal
constituents
Very high production cost
Drug leakage/ entrapment/ drug fusion
Sterilization
Short biological activity / t ½
Oxidation of bilayer phospholipids and low solubility
Rate of release and altered bio distribution
Extensive clinical and laboratory research to a
certain long circulating liposomes
Repeated i.v. administration problems
