DRUG-RELEASE FROM HYDROCOLLOID EMBEDDINGS WITH HIGH OR LOW SUSCEPTIBILITY TO HYDRODYNAMIC STRESS

Purpose. The subject of the study was the influence of hydrodynamic st ress on the drug release from direct compressed hydrocolloid embedding s. Additionally a correlation between the release kinetics and differe nt polymer characterising parameters was attempted. Methods. The drug release was fitted to an expanded Korsmeyer equation to describe the r elease kinetics. The influence of the stirring rate of the paddle in t he USP paddle apparatus on the Mean Dissolution Time (MDT) was express ed as quotient of the MDT's at the stirring rate of 200 and 100 min(-1 ) Results. If the drug release followed the square root of time kineti cs, nearly no effect of the agitation speed on the release rate was ob served. To achieve this diffusion controlled drug release the developi ng gel layer had to be hydrated very well and resistant against erosio n (viscosity of at least 4000 mPa . s of the 2% polymer solution and a small expansion of the swelling gel especially at the beginning of th e release). The erosion controlled zero order release was generally mu ch affected by the hydrodynamic stress except for some hydrocolloids w ith incomplete swelling. Thus, it was possible to define a new release mechanism, the polymer particle erosion. The drug release was control led by the attrition of partially swollen polymer particles and not by the polymer dissolution or drug diffusion. Conclusions. Polymer parti cle erosion or diffusion control should be the release controlling mec hanisms for negligible influence of hydrodynamic stress.