In the master’s thesis, we studied the influence of a poorly water-soluble model drug substance and granulation liquid addition on the release from granules.
We granulated two laboratory batches or twelve sub-batches of a poorly water-soluble model drug substance with two different particle size distributions in a high-shear granulator under the same conditions. We used water as the granulation liquid. To calculate the addition of granulation liquid at the endpoint, we used the equation correlating model drug substance particle size with the required amount of granulation liquid that was determined in preliminary experiments. Based on the equation, more granulation liquid had to be used in case of larger model drug substance particles (MU19) compared to smaller particles (MU20). During granulation, samples were taken at six points with different amounts of added granulation liquid and further processed.
The produced granules and both batches of the drug substance were evaluated for wettability (contact angle measurement), specific surface area, and morphological properties (scanning electron microscope). We also determined loss on drying of granules (after granulation and after drying), their particle size distribution, and release in an aqueous medium with polysorbate 80.
Morphologically, both active ingredients have a needle-like structure. The wettability of the drug substance with smaller particles MU20 was higher (smaller contact angle) than the wettability of the drug substance with larger particles MU19. In addition, MU20 had a higher specific surface area and higher surface energy. Contact angle of the final blend containing MU19 was larger than the one containing MU20. With these results we explained the difference in required water for granulation between both batches of drug substance.
Dissolution tests showed that the fraction of smaller granules dissolved significantly faster than the fraction of larger granules from the same granulation point. In addition, granules with a smaller amount of added granulation liquid dissolved faster than those with a higher amount.
However, we also encountered surprising results, as 019G granules with larger drug substance particles dissolved faster than 020G granules with smaller drug substance particles, which could be due to less dense structure and better wettability of 019G granules and greater hydrophobicity of 020G granules.
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