(615f) Evaluation of Shear Induced Hydrophobicity and Drug Release

The purpose of this study was to investigate the effect of shear on hydrophobicity and drug release with respect to blend composition and particle size. A very strong influence of shear on hydrophobicity and drug release was found in the case of blends consisting of magnesium stearate and silica. Four formulations of pharmaceutical powder blends were subjected to three different shear strain conditions (40 rev, 160 rev and 640 rev) in a shear cell rheometer at a shear rate of 80 rpm. A total number of twelve blends were tested for hydrophobicity. Tablets were compressed at 12 kN in a rotary tablet press. During the tablet compression, powder samples were collected after the feed frame and their hydrophobicity was again measured. Dissolution studies were preformed on the tablets pressed from all the sheared blends. Hydrophobicity and dissolution parameters were analyzed to study the influence of shear on drug release of tablets. Results indicated that increase in shear strain could significantly increase hydrophobicity. Interestingly, the increase in hydrophobicity with shear was found to predominantly depend upon the blend composition. Blends with colloidal silica and magnesium stearate were found to show higher hydrophobicity with shear than other blends. Shear caused by feed frame was found to be effective in changing the particle hydrophobicity only in the absence of MgSt. Studies showed that the drug release rates dropped with shear more for the blends with colloidal silica and magnesium stearate than the other blends. Further, the rate of drug release dropped with decrease in particle size of excipient. Surprisingly, the relative increase in hydrophobicity with a corresponding drop in the drug release rate was not found when either of MgSt or colloidal silica was mixed alone in the blends.