Modelling of drug release from ensembles of aspirin microcapsules of certain particle size distribution

Purpose: In order to determine the drug release profile of an ensemble of aspirin crystals or microcapsules from its particle distribution a mathematical model that considered the individual release characteristics of the component single particles was developed. The model assumed that under sink conditions the release from individual (component) particles would be independent of each other and hence simply additive. Method: The release parameters, mt = the amount of drug released in time t, m∞ = the maximum release and t∞ = the time to attain it were determined for each single particle by simulation using previously derived mathematical models. To obtain the cumulative release curve for the ensemble the individual releases were summed up at each time scale and for the various time intervals. Values of m∞ and t∞ for the ensemble were obtained from the simulated cumulative curves. The release profiles of the ensembles were also determined experimentally and their m∞ and t∞ values deduced from the release curves. Results: The observed cumulative curves of the ensembles compared favourably with the simulated data. The % difference in the observed and the simulated m∞ and t∞ values of the ensembles was within ± 20%, which indicated that the modelling was valid. Conclusion: The study showed that the release profile of an ensemble can be determined from its particle distribution which has application in controlled release studies.