Unexpected differences in dissolution behavior of tablets prepared from solid dispersions with a surfactant physically mixed or incorporated

In a previous study, it was shown that the incorporation of poorly soluble drugs (BCS class II) in sugar glasses could largely increase the drug's dissolution rate [van Drooge, D.J., Hinrichs, W.L.J., Frijlink, H.W., 2004b. Anomalous dissolution behaviour of tablets prepared from sugar glass-based solid dispersions. J. Control. Release 97, 441–452]. However, the application of this technology had little effect when high drug loads or fast dissolving sugars were applied due to uncontrolled crystallization of the drug in the near vicinity of the dissolving tablet. To solve this problem a surfactant, sodium lauryl sulphate (SLS), was incorporated in the sugar glass or physically mixed with it. Diazepam and fenofibrate were used as model drugs in this study. The dissolution behavior of tablets prepared from solid dispersions in which SLS was incorporated was strongly improved. Surprisingly, the dissolution rate of tablets prepared from physical mixtures of SLS and the solid dispersion was initially fast, but slowed down after about 10 min. The solid dispersions were characterized by DSC to explain this unexpected difference. These measurements revealed the existence of interaction of SLS with both the drug and the sugar in the solid dispersion when SLS was incorporated. It is hypothesized that due to this interaction, the dissolution of SLS was slowed down by which a high solubility of the drug in the near vicinity of the dissolving tablet is maintained during the whole dissolution process. Therefore, uncontrolled crystallization is effectively prevented.