Tableting properties of silica aerogel and other silicates.

CONTEXT: In solid oral dosage forms silicates are commonly used as glidants in low concentration. However, due to their large specific surface area, silicates may also be used as carrier materials for drugs. Moreover, silicates allow amorphisation of drugs by co-grinding or processing with supercritical fluids. OBJECTIVE: The aim of this study was to investigate the physical and the tableting properties of Silica Aerogel (special type of silica with an extremely large specific surface area), Neusilin(®) US2 (magnesium aluminometasilicate), Florite(®) (calcium silicate) and Aerosil(®) 200 (colloidal silica). MATERIALS AND METHODS: Powder blends of Avicel(®) PH102 (microcrystalline cellulose) and different amounts of the respective silicate were compacted and analyzed for their tabletability (tensile strength vs. compaction pressure) as well as their Heckel plot. RESULTS AND DISCUSSION: With Neusilin(®) the tabletability appeared to be independent of the silicate concentration, whereas with Florite(®) an increasing silicate concentration led to a higher tensile strength. In contrast, the addition of Silica Aerogel and Aerosil(®) resulted in a decrease of the tensile strength. With Aerosil(®) a maximum tolerable concentration of 20% [w/w] was determined. Plastic deformation of all powder blends decreased with increasing silicate concentration. This effect was most pronounced with Aerosil(®) and least with Florite(®). CONCLUSION: Tablets with acceptable tensile strength were obtained with all plain silicates except for Aerosil(®). Therefore, these silicates may be used in tablet formulations, e.g. as carrier materials for liquid or amorphous drugs.

Enhancement of griseofulvin release from liquisolid compacts.

The potential of hydrophilic aerogel formulations and liquisolid systems to improve the release of poorly soluble drugs was investigated using griseofulvin as model drug. The in vitro release rates of this drug formulated as directly compressed tablets containing crystalline griseofulvin were compared to aerogel tablets with the drug adsorbed onto hydrophilic silica aerogel and to liquisolid compacts containing the drug dissolved or suspended in PEG 300. Furthermore, the commonly used carrier and coating materials in liquisolid systems Avicel® and Aerosil® were replaced by Neusilin®, an amorphous magnesium aluminometasilicate with an extremely high specific surface area of 339 m²/g to improve the liquisolid approach. Both the liquisolid compacts containing the drug dissolved in PEG 300 and the aerogel tablets showed a considerably faster drug release than the directly compressed tablets. With liquisolid compacts containing the drug suspended in PEG 300, the release rate increased with rising fraction of dissolved drug in the liquid portion. It could be shown that Neusilin® with its sevenfold higher liquid adsorption capacity than the commonly used Avicel® and Aerosil® allows the production of liquisolid formulations with lower tablet weights.

Comparison of traditional and novel tableting excipients: physical and compaction properties.

CONTEXT: Novel tableting excipients are continuously developed and advertised with superior flow and compaction characteristics. OBJECTIVE: The objective of this study was to compare two traditionally used and two novel tableting excipients with regard to their physical and tableting properties as well as their magnesium stearate sensitivity. Avicel(®) PH102 (microcrystalline cellulose) was compared to the novel co-processed excipient Prosolv(®) SMCC90 (silicified microcrystalline cellulose), whereas Anhydrous Emcompress(®) (anhydrous dicalcium phosphate) was compared to the novel spherically granulated excipient Fujicalin(®) (anhydrous dicalcium phosphate). MATERIALS AND METHODS: True density, particle size, specific surface area (SSA), flowability, tabletability, and magnesium stearate sensitivity of the excipients was determined. RESULTS AND DISCUSSION: Due to the silification process (Prosolv(®)) and the unique manufacturing process (Fujicalin(®)), the novel excipients showed a comparably larger SSA. Hardest tablets by far could be obtained with Prosolv(®), followed by Avicel(®) and Fujicalin(®). Avicel(®) and Prosolv(®) were sensitive to magnesium stearate, whereas Fujicalin(®) and Emcompress(®) did not show lubricant sensitivity. This confirms the plastic deformation behavior of microcrystalline cellulose and the brittle fracture of anhydrous dicalcium phosphate. CONCLUSION: Compared to the traditional excipients the investigated novel tableting excipients were advantageous with regard to their SSA and their tableting properties.