Formulation and evaluation of novel in situ gel-forming systems for nasal delivery of drug- a review

For locally acting intranasal drugs, an extended residence time in the nasal cavity is desirable and related to a prolonged effect. A gel is a soft, solid or solid like material consisting of two or more components, one of which is a liquid, present in substantial quantity. Gels do not flow under die influence of their own weight. Reversible gels refer to those that have die capacity to make, break and modify the bonds responsible for holding the network together. Gels that do not have this capability because they are held together are termed as permanent gels. Although many gels exhibit shear-thinning behavior, they cannot be easily delivered to the nasal cavity using normal droppers and spray devices because nasal cavity is an irregularly shaped space and it has folded structure. Hiesame limitation is applicable to powdered formulations. Liquid drops given by nasal route have a low nasal residence time, which is insufficient for drug absorption and the formulation sometime gets drained in the oral cavity.
Thus it will be advantageous to use a stimulus sensitive gel system that will provide the advantages of free flowing liquid till it reaches the surface of mucous and get converted into gel form when it is in contact with mucosal surface so that it will have improved nasal residence time for effective absorption of drug. This type of system will provide the patient convenience of application of formulation. Also a sustained release formulation of this nature will reduce the frequency of drug administration and will improve patient compliance.
Poloxamer 407 (Pluronic F - 127) exhibit the phenomenon of reverse-thermal gelation, i.e., the polymer exists a mobile viscous liquid at reduced temperatures, bid forms a rigid semisolid gel network with an increase in temperature. Poloxamer is nontoxic and also it functions as surfactant and solubilizing agent. But it is reported that the rate of gelation and the temperature of the sol-to-gel transition for poloxamer 407 are concentration dependent. Thus to have a thermo reversible gel with gelation temperature in the range of 34°C - 37°C optimization is need with respect to the drug, polymer and other formulation, excipients added to it. The present project involves designing of thermo reversible gel formulations suitable for nasal administration of certain drugs.