The total fraction of API released after 24 h was approximately the same for all compositions–between ∼80 and ∼95%, with the values for Fentanyl being somewhat higher than those for Zolpidem–except for the compositions that contain high amounts of silica and simultaneously low amount of water (high Si/Al ratio and low H2O/SiO2 ratio, Table 1); viz. Zol1–3, and Zol5 as well as Fen3 and Fen5.