In-vitro studies of tizanidine controlled-release microcapsular matrices

Oral microencapsulated controlled release preparations of tizanidine (TIZ) were tried. The designed system is able to maintain plasma concentration without the need of frequent dosing and reduce side effects unlike in case of conventional dosage form. Microcapsules were prepared by modified solvent evaporation technique using different proportions of cellulose acetate. The microcapsules (TIZ1, TIZ2 and TIZ3) were compressed in to tablets (T-TIZ1, T-TIZ2 and T-TIZ3) for oral delivery. The prepared microcapsules were white, free flowing and spherical in shape with the particle size varying from 175.92 +/- 9.82 to 194.94 +/- 14.28 mu. The t60% of TIZ release from microcapsules was found to be 2.39+/-0.6, 3.39+/-0.6 and 4.55+/-0.8 h respectively for formulation TIZ1, TIZ2 and TIZ3 while their tablets i.e., T-TIZ1, T-TIZ2, T-TIZ3 and marketed SR were in 5.28+/-1.5, 6.86+/-0.6, 8.25 +/-0.6 and 3.75+/-1.20 h respectively indicating more extension of time in tablet than microcapsules. The mechanism of drug release from tizanidine microcapsules and their tablets were studied by using Higuchi and Korsmeyer-Peppas models. The r-value for TIZ1, TIZ2 and TIZ3 indicates diffusion controlled with first order kinetic. The value of exponent coefficient (n) for T-TIZ1, T-TIZ2 and T-TIZ3 were found to be 0.844, 0.901 and 0.914 indicating anamolous, case-II and case-II transport release mechanism respectively.