investigation into the drug release from ibuprofen matrix tablets with ethylcellulose and some poly-acrylate polymers

This study was performed to achieve sustained-release Ibuprofen matrix tablets with a zero-order release kinetic while most of the previous formulations have shown Higuchi release kinetic. Considering the results from previous studies, ethyl cellulose, Carbopol 934P, Carbopol 974P, and Pemulen TR-1 were used at different amounts for preparation of the tablets by direct compression. The release profiles were studied in a two-stage release test using nonlinear regression analysis. Carbopols 934P and 974P could not sustain the release adequately while Pemulen TR-1 had too strong sustaining effect. Therefore, combination formulations were considered and studied. The release profiles of ethyl cellulose formulation and the combination formulation consisting Carbopol 934P and Pemulen TR-1 best fitted in Higuchi model, although the zero-order model was not completely rejected. However, the kinetic model of release from the combination formulation consisting Carbopol 974P and Pemulen TR-1 changed to zero-order indicating the most constant release rate among formulations. This was speculated to be due to some erosion of the gel, as well as some interaction of the hydrophobic chain of Pemulen TR-1 with Ibuprofen. Therefore, this formulation is suggested for directly compressed sustained-release matrix tablets of Ibuprofen with a more constant release rate.

investigation into some effective factors on encapsulation efficiency of alpha-tocopherol in MLvs and the release profile from the corresponding liposomal gel

Vitamin E [alpha-tocopherol] is a natural antioxidant very useful for preventing the harmful effects of UV sun rays as skin aging and cancers. In this study, different MLV formulations were made using egg lecithin and varying molar ratios of alpha-tocopherol and/or cholesterol, and their encapsulation efficiencies were determined. The best liposomal product was incorporated into a carbomer 980 gel. The resulting preparation was then studied with regard to the rheology and release profile using r[2] values and Korsmeyer-Peppas equation. The encapsulation efficiency was dramatically decreased when using alpha-tocopherol at molar ratios of 1:10 or more, which is suggested to be due to the defect in regular linear structure of the bilayer membrane. Addition of cholesterol to formulations caused a decrease in encapsulation efficiency directly related to its molar ratio, which is due to the condensation of the bilayer membrane as well as competition of cholesterol with alpha-tocopherol. The liposomal gel showed a yield value of 78.5 +/- 1.8 Pa and a plastic viscosity of 27.35 +/- 2.3 cp. The release showed a two-phase pattern with the zero-order model being the best fitted model for the first phase. However, the "n" and r[2] values suggested a minor contribution of Higuchi model due to some diffusion of alpha-tocopherol from the outermost bilayers of the MLVs to the gel. The second phase showed a non-Fickian release indicating a more prominent role for diffusion. This combinational release profile provides a high initial concentration of alpha-tocopherol followed by a slow release throughout a 10 h period

Preparation of urea-containing stable plurilamellar liposomes and studying the effect of cholesterol on their encapsulation efficiency and release rate

Liposomes have attracted much attention as a novel drug delivery system for controlled and/or targeted release of drugs. In reverse-phase evaporation, which is a well-known method of preparation for LUVs and SPLVs, the phospholipid concentration affects the preparation process, as well as characteristics of the resulting liposomes. Drug release rate from liposomes depends on permeability of the liposomal membranes. Cholesterol [CH] is quite often included in liposomal membranes to reduce their permeability to water-soluble molecules. In this study, the required concentration of the phospholipid Ovotin' 160 [O160] for the preparation of urea-containing stable plurilamellar vesicles, and the effect of different percentages of cholesterol on the encapsulation parameters and release rate of urea as a water-soluble model drug were investigated. The results show that there is a critical concentration of the phospholipid, under which the capability for the formation of a stable emulsion [in the emulsification part of the preparation process] sharply decreases. The release rate and encapsulation parameters increased when the molar ratio of cholesterol to O160 was 5% and decreased with the ratios of 50% and 100%. Therefore, in preparation of the optimum samples a balance between the encapsulation parameters as well as the release pattern should be considered carefully