Semisolid topical formulations containing nimesulide-loaded nanocapsules, nanospheres or nanoemulsion: development and rheological characterization.

The objective of this work was to develop and characterize semisolid topical formulations containing nimesulide-loaded nanospheres, nanocapsules or nanoemulsion. The nanoprecipitation and spontaneous emulsification methods were used to prepare the colloidal suspensions and the nanoemulsion. The hydrodynamic diameters were 282 nm for the nanoemulsion, 293 nm for the nanocapsules and 191 nm for the nanospheres containing nimesulide. The encapsulation efficiencies were close to 99% in all cases and pH values ranged between 5.1 and 5.3. Each drug-loaded nanocarrier formulation was incorporated in Carbopol 940 gels. The semisolid dosage forms showed yellowish, glossy and homogeneous aspect after the incorporation of the colloidal suspensions and nanoemulsion. The recovery of nimesulide and the pH values for the gels containing nanoemulsion, nanospheres or nanocapsules remained constant during storage (120 days). For all formulations, the rheograms exhibited a non-Newtonian behavior presenting pseudoplastic characteristics and shear thinning. The rheograms were adjusted to Ostwald's model showing regression coefficients higher than 0.9900. None thixotropic phenomenon was experimentally detected under the test conditions for all formulations.