Abstract
A novel liposome-in-microsphere (LIM) formulation has been created comprising drug-loaded liposomes within pH responsive Eudragit S100 microspheres. The liposomes contained the model drug 5-ASA and were coated with chitosan in order to protect them during encapsulation within the microspheres and to improve site-specific release characteristics. In vitro drug release studies showed that LIMs prevented drug release within simulated stomach and small intestine conditions with subsequent drug release occurring in large intestine conditions. The formulation therefore has potential for oral colonic drug delivery.
Highlights
Within oral drug delivery, specific targeting of the colon can be advantageous due to near-neutral pH, low enzyme and bile salt activity and long residence time
For both anionic and neutral liposomal formulations no further change in zeta potential was observed once the concentration of the chitosan coating solution had reached 1% indicating that vesicle surfaces were saturated at this point
It is thought that electrostatic interactions dominate in the coating of anionic liposomes with cationic chitosan [21, 22] while hydrophobic interactions are important for neutral liposomes, with hydrogen bonding occurring between the chitosan and phospholipid head groups of the lipid bilayer [22]
Summary
Specific targeting of the colon can be advantageous due to near-neutral pH, low enzyme and bile salt activity and long residence time. It has been shown that specific targeting to the colon is advantageous for systemic treatments for a number of reasons including the potential for protein and peptide drug absorption [1, 2]. Oral drug delivery to the colon is associated with a number of obstacles including dosage form transit through regions of high acidity and digestive activity. Coating them with a polymer is one way that may protect them during transit, but very little work has been done on targeting the colonic region
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