There is an increasing interest in using polyols, such as sorbitol, in pharmaceutical tablet formulations due to their sweet taste and reduced calorie content and noncariogenic characteristics. Sorbitol is a common tableting excipient and plays a major role in the manufacture of chewable and sublingual tablets. One limitation of sorbitol as a tableting excipient is that its hygroscopic nature may cause pronounced friction, as well as, sticking to the punch surfaces. Therefore, the aim of the present study was to evaluate the suitability of various lubricants for reducing friction and preventing sticking during the compaction of sorbitol-containing tablets. The efficiency of the most commonly used lubricant, magnesium stearate, was compared to that of sodium stearyl fumarate (PRUV®*), microprilled poloxamer 407 (Lutrol® micro 127**) and PEG 4000. Compaction studies were performed using both an eccentric tablet press and a rotary tablet press. In addition to their compaction properties, the effect of the investigated lubricants on the tablet properties was evaluated. Considering both the lubricant efficiency and the influence on tablet properties of the investigated lubricants, PRUV® was found to be most suitable for compaction of the investigated sorbitol tablet formulations. However, the best overall lubricant performance, accompanied by excellent tablet properties, was observed with a mixture (1:1) of magnesium stearate and PRUV®, indicating synergism between these lubricants.
*PRUV® is registered trademark of JRS Pharma
**Lutrol® is registered trademark of BASF
Several crystal structures of sorbitol may be encountered. Eleven sorbitol samples from five different manufacturers were studied by x-ray diffraction and differential scanning calorimetry. Three crystalline forms were identified. The γ form is the most stable. One of these samples was constituted by the pure γ form.
Sorbitol is usually considered as a very hygroscopic excipient. We studied this most stable sorbitol for its technological and biopharmaceutical properties in tablet formulation.
Aspirin and acid ascorbic tablets were prepared with γ sorbitol as a diluent, in high concentration, by direct compression. Three disintegrants were tested : maize starch, Kollidon® CL*, Ac-Di-Sol®**. Using either lactose or γ sorbitol as a diluent, different batches of tablets were prepared with the same proportion of diluent and in the same conditions.
Compression properties, hardness, disintegration time, dissolution rate and stability in moist conditions were studied.
The tablets containing γ sorbitol show :
- A better ratio compression force/hardness.
- A longer time of disintegration and dissolution
- The very great importance of the choice of the disintegrant : Ac-Di-Sol® was much better than Kollidon® CL or maize starch in this case of formulation : conserved during one year at 80 % Relative Humidity, tablets with γ sorbitol and Ac-Di-Sol® kept their aspect and their biopharmaceutical properties very well. A slightly greater acid ascorbic alteration with sorbitol as a diluent than with lactose can be noticed.
It seems that γ sorbitol is a stable diluent if the Relative Humidity is lower than 80%. Then it should be avoided with drugs too sensitive to moisture like ascorbic acid.
In spite of a slower release time, its hardening power and its very good compression properties can be of great interest.
*Kollidon® is registered trademark of BASF **Ac-Di-Sol® is registered trademark of DuPont