Long-term stability studies. For long-term stability studies, formulated IBU was stored at ambient conditions (≈25 °C). The samples were collected at day 0, 1, 8, 20, 30 and day 60. Before the determination of the drug loading by HPLC, all samples were centrifuged for 5 min at 9000 rpm with a MIKRO 185 (Hettich, Tuttlingen, Germany). Long-term stabilization experiments were performed with three individually prepared samples and results are presented as means ± SD, quantification was carried out as described previously.