Chitosan in situ gelation for improved drug loading and retention in poloxamer 407 gels.

A method for the in situ gelation of poloxamers and the mucoadhesive polymer chitosan has been developed by exploiting the tendency of poloxamer solution to form gel at physiological temperatures and of chitosan (CT) to form ionotropic gel structures in the presence of sodium tripolyphosphate (TPP). Novel poloxamer gels containing CT-TPP complex formed in situ during the administration were prepared by mixing poloxamer-CT and poloxamer-TPP solutions in double syringes. The micellization and gelation of poloxamer 407 in the presence of chitosan and/or TPP were studied using differential scanning calorimetry and tube inversion; both additives were found to reduce the critical micellization temperature and critical gelation temperature of poloxamer aqueous solution. The poloxamer gels containing CT-TPP complex formed in situ were found to exhibit reduced dissolution rate and superior release characteristics with three different drugs--metoprolol, doxycycline and flufenamic acid. Furthermore, by varying the compositions of the two solutions independently, it is possible to control the pH in a way to suit the solubilization of a drug as well as the specific environment of a particular application site. By varying the concentrations of chitosan, TPP and poloxamer, the delivery system can be fine-tuned to afford gels with specific properties, ranging from nanoparticle suspensions to semisolid gels. These in situ gels have the potential to increase the utility of thermo-reversible poloxamers in drug delivery.