Direct compression characteristics of xylitol

The effect of relative humidity and formulation variables on chewable xylitol-sorbitol tablets

Changing relative humidity levels challenge the manufacturing of chewable xylitol-sorbitol based tablets. The aim of the study is to investigate how the formulation of chewable xylitol-sorbitol tablets affects the properties of the powder blends and the tablets in an environment of different relative humidity levels. In all, 30 batches containing different ratios of sorbitol, xylitol and magnesium stearate were prepared at three different relative humidity levels. Powder blends were made into tablets using an instrumented eccentric tableting machine. To demonstrate the effect of variables on powder blend and tablet properties, multiple linear regression analysis was performed. It was found that xylitol-sorbitol powder blends and tablets benefitted from the large amount of magnesium stearate, and the high lubricant level negatively affected the quality of the tablets only at high relative humidity. In the presence of high environmental humidity, the amount of sorbitol in the powder mixture must be limited in order to prevent sticking whereas at low relative humidity, higher content of sorbitol is needed to decrease the friability of tablets. Results indicate that alternating relative humidity levels truly challenge the production of xylitol-sorbitol based tablets and if the humidity is not controllable, there is a need for additional filler-binders.

Polyols as filler-binders for disintegrating tablets prepared by direct compaction

BACKGROUND

Although polyols are frequently used as tablet excipients in lozenges, chewing tablets, and orodisperse tablets, special directly compressible (DC) forms are recommended as filler-binder in common disintegrating tablets.

AIM

In this article, DC types of isomalt, lactitol, mannitol, sorbitol and xylitol are evaluated.

METHOD

Tablets of both lubricated and unlubricated DC polyols and theophylline tablets were compressed at different forces using a compaction simulator or a motorized hydraulic press. Disintegration times (without disks) and dissolution rate were measured according to Ph.Eur.

RESULTS

Compaction profiles show that the DC forms of isomalt, mannitol and sorbitol have sufficient compactibility and a low lubricant sensitivity. The crushing strengths of tablets, prepared from DC lactitol and xylitol, are too low for practical use. Because of their reduced hygroscopicity and smaller capping tendency as compared with DC sorbitol, DC types of isomalt and mannitol seem to be the most convenient filler-binders. Because of their high water solubility, tablets prepared from polyols erode rather than disintegrate. Tablet formulations with theophylline as a test drug and DC isomalt or DC mannitol as filler-binder show that both products have their own limitations: DC mannitol gives more adhesion problems than DC isomalt. On the other hand, the disintegration time and drug dissolution rate for tablets containing DC mannitol is faster than for tablets containing DC isomalt.

CONCLUSIONS

Of the DC polyols investigated, both DC isomalt and DC mannitol are the most suitable filler-binders for disintegrating tablets, prepared by direct compaction.

Excipients for Direct Compaction—an Update

In 1996, Bolhuis and Chowhan compiled a review of excipients that were used for the direct compaction of tablets. This article updates that review because since that time there has been considerable activity in this area. New single component and coprocessed filler-binders have been introduced. In addition, there have been advances in the understanding of how such substances act and hence how they can be optimally designed.

Highly compressible paracetamol - II. Compression properties

Paracetamol particles crystallized in the presence of polyvinylpyrrolidone (PVP) exhibited an obvious improvement in their compression properties compared to untreated paracetamol. Paracetamol particles crystallized in the presence of 0.5% w/v PVP 10000 or PVP 50000 produced tablets with improved crushing strength with no tendency to cap even at high compression speeds. The very low values of strain rate sensitivity (SRS) and the lack of reduction in crushing strength with increasing compression speed for these particles, were indicative of a high degree of fragmentation during compression. The results of elastic recoveries and elastic energies of tablets were indicative of much less elastic behaviour of these particles than untreated paracetamol. The low elastic energy/plastic energy (EE/PE) ratio for paracetamol crystallized in the presence of PVP indicated that, contrary to untreated paracetamol, a minor portion of compression energy was utilized as elastic energy.

Characterization and evaluation of isomalt performance in direct compression

Isomalt is a sugar substitute with a wide range of potential pharmaceutical applications as a result of its physicochemical properties. Four grades of this material were evaluated for their physical characteristics. Only Palatinit(R) C and F exhibited potential characteristics for direct compression. As expected, the products required lubrification for tabletting. A level of 1% lubricant gave the best performance for Palatinit(R) C, the most compressible grade as shown by compaction profiles generated using a single-punch machine. However, its flow behaviour had to be improved by including 0.5% Aerosil(R) 200 as shown by tablet weight uniformity data. Further evaluation by Heckel analysis showed that isomalt exhibited plastic behaviour and underwent elastic recovery primary in the die. Its dilution potential was examined using powdered paracetamol. Acceptable tablets were produced up to 30% drug dilution, but the tensile strength values were reduced, disintegration time and friability increased as expected. Drug dissolution profiles showed a decreasing dissolution rate with the increase of compression force and drug concentration, but considerable improvement was noted when a disintegrant was included. The physical characteristics of the tablets were relatively stable after half a year storage at different humidities as a result of the low hygroscopicity of isomalt.

Effect of compression speeds on the compaction properties of a 1:1 paracetamol-microcrystalline cellulose mixture prepared by single compression and by combinations of pre-compression and main-compression

A 1:1 blend of paracetamol and microcrystalline cellulose was compacted at different compression speeds by single compression or combinations of pre- and main-compression. The tensile strengths of the tablets decreased from 0.74+/-0.01 to 0.44+/-0.05 MPa as the compression speed was increased from 78 to 390 mm/s when a single compression pressure of 80 MPa was used to compress the tablets. When combinations of pre- and main-compression of 320 and 240 MPa were used to compress the tablets, tensile strengths decreased from 3.12+/-0.67 MPa at a compression speed of 78 mm/s to 1.24+/-0.36 MPa when the compression speed was 390 mm/s. The energies of compression and the ratio of elastic to plastic energies increased with increase in compression speed. This was because the material was becoming more elastic and more energy was required for the elastic expansion leading to a reduction in the energy available for plastic deformation and bond formation which resulted in a decrease in tensile strengths. Pre-compression played a major role at high compression speeds. The tensile strengths of tablets (1.2+/-0.08 MPa) compressed with a pre-compression of 160 MPa followed by a main-compression of 80 MPa (compression speed of 390 mm/s) were similar to the tensile strengths of tablets (1.1+/-0.10 MPa) compressed using a single compression of 320 MPa at the same compression speed of 390 mm/s. Thus, combinations of lower pressures can be employed to compress the material to the same tensile strength as a high single compression.