Magnesium stearate (MgSt; Covidien, Dublin, Ireland) or sodium lauryl sulfate (SLS; Ward's Science, Rochester, NY) was used as lubricant. Celecoxib, a BCS class II drug (weak acid with p K a of 11.1), was selected as a model drug because of its low solubility, about 3.3 µM in water at 25 °C ( EPA, 2010 ).