Abstract

Adsorption of lipid-based formulations, which are usually liquid, onto silicas has been extensively investigated in the past decade to convert them into solid dosage forms. There are conflicting reports on the ability of commercially available porous silicas, like Neusilin® US2, to release lipid formulations completely, especially after long-term storage. In this study, the release of a model drug, probucol, from different formulations of medium chain lipids and a surfactant, Kolliphor EL (Cremophor EL) or polysorbate 80, were studied after adsorbing them onto Neusilin® US2. Complete drug release (> 80%) was obtained from all formulations on Day 1; however, the extent of drug release decreased progressively with time. The decrease was dependent on the relative hydrophilicity of the formulations.

The maximum decrease (< 10% drug released on day 60) was seen from formulations containing the highest amount of lipid (70% in the SEDDS preconcentrate) and lowest decrease was seen in formulations containing the drug dissolved in the neat surfactant only (ca. 65% drug released on day 60). Precoating Neusilin® US2 with polyvinylpyrrolidone (PVP), by treating the silicate with an alcoholic solution of PVP and then drying, eliminated or minimized the decrease in drug release upon storage, possibly by blocking the mesoporous region of the silicate and improving hydration and allowing emulsification of the formulations within the larger pores. Formulations containing PVP K-90 precoated on Neusilin® US2 exhibited complete drug release (> 80%) even after 6 months of storage.

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