The effects of polymorphism, particle size and compression pressure on the dissolution rate of phenylbutazone tablets

Investigation of the effects of particle size on fragmentation during tableting

Particle size is a critical parameter during tablet production as it can impact tabletability, flowability, and dissolution rate of the final product. The purpose of this study was to investigate the effect of initial particle size on fragmentation of pharmaceutical materials during tableting. Initial particle size fractions ranging from 0-125 to 355-500 µm of dibasic calcium phosphate (DCP), lactose monohydrate, and agglomerated and non-agglomerated microcrystalline cellulose (MCC) were blended with magnesium stearate and compressed into tablets. Larger initial particle sizes were found to fragment more extensively than smaller initial particle sizes for all materials based on the particle size distributions determined by laser diffraction. DCP was found to fragment most extensively followed by lactose and both MCCs. The fragmentation degrees of DCP, lactose, agglomerated and non-agglomerated MCC reached 95, 81, 32, and 29%, respectively. These findings were further supported by an increase in specific surface area with increasing compression pressure of compressed particles. The NIR spectral baseline offset from tablets was found to increase with increasing compression pressure up to 50 MPa for all materials, which was the same compression pressure range where fragmentation was observed. The NIR spectral slope from tablets as a function of compression pressure furthermore showed a similar trend as the tabletability profiles. NIR spectroscopy can thereby potentially be used as a surrogate control strategy for assessing compression related particle size changes and possibly tablet density and deformation behavior during tablet production.

Novel solid forms of oxaprozin: cocrystals and an extended release drug–drug salt of salbutamol

Novel solid forms of an anti-inflammatory drug, oxaprozin, were identified. A drug–drug salt of oxaprozin with salbutamol was proved promising for development of extended release tablet formulations of salbutamol.

Influence of crystal structure on the tableting properties of sulfamerazine polymorphs

PURPOSE

To understand the influence of polymorphic structure on the tableting properties of sulfamerazine.

METHODS

Bulk powders of sulfamerazine polymorph I and of two batches. II(A) and II(B) of different particle size, of polymorph II were crystallized. The powders were compressed to form tablets whose porosity and tensile strength were measured. The relationships between tensile strength, porosity and compaction pressure were analyzed by the method developed by Joiris. E., et al. Pharm. Res. 15:1122-1130 (1998).

RESULTS

The sensitivity of tensile strength to compaction pressure, known as the tabletability, follows the order. I >> II(A) > II(B) and the porosity at the same compaction pressure, which measures the compressibility, follows the order, I << II(A) < II(B). Therefore. the superior tabletability of I over II(A) or II(B) is attributed to its greater compressibility. Molecular simulation reveals slip planes in crystals of I but not in II. Slip planes provide I crystals greater plasticity and therefore greater compressibility and tabletability. Larger crystal size of II(B) than of II(A) leads to fewer contact points between crystals in the tablets and results in a slightly lower tabletability.

CONCLUSIONS

Slip planes confer greater plasticity to crystals of I than II and therefore greater tabletability.

Effect of compression speed on the tensile strength of tablets of binary mixtures containing aspirin

Mixtures of aspirin with sodium chloride, sucrose, Starch 1500 or Emcompress have been compressed to two maximum upper punch pressures at two compression speeds. Non-linear relationships between tensile strength and composition, and tablet porosity and composition were found in all cases. Tablets of the individual materials compressed at fast speed showed either little change or a reduction in tensile strength when compared with those compressed at slow speed. For mixtures of aspirin with Starch 1500, tablets compressed at fast speed were weaker and more porous than those compressed at slow speed. However, some mixtures of aspirin with sodium chloride, sucrose or Emcompress gave tablets with greater tensile strength and lower porosity when prepared at fast compression speed compared with tablets prepared at slow speed. This behaviour was attributed to the modification of the consolidation behaviour of the aspirin by the second material.

An evaluation of the relative importance of formulation and process variables using factorial design

A factorial design method for assessing the relative importance of various formulation and process factors and their interactions in model paracetamol tablets is described. The design was a 2 X 2 X 2 X 3 type using mixing time, starch concentration, drug particle size and compaction pressure respectively. The starch concentration was the most significant factor in affecting the dissolution rate but the larger drug particle size also gave a significant increase in drug release rate. Interactions between starch concentration and drug size and between these and mixing time were also observed. The most significant factor affecting the tensile fracture stress of the tablets was the mixing time, followed in order by the drug particle size, starch concentration and compaction pressure.

Kinetic study of the polymorphic transformations of phenylbutazone

The polymorphic transformations of phenylbutazone from metastable forms alpha and beta to stable form delta were studied quantitatively at four temperature and five humidity levels by X-ray powder diffractometry. The transformation of form alpha conformed with the Avrami-Erofe'ev kinetic model and form beta conformed with apparent first-order kinetics. In the two transformation systems, the induction periods depended on the storage conditions and were prolonged with lowering of temperature and humidity. The transformation rate of form alpha was not affected by humidity, whereas that of form beta increased according to a rise in humidity. The temperature dependency of the transformation rate constant was remarkable. The Arrhenius treatment was applicable to the beta----delta transformation at low temperatures. The overall half-life, including induction period, revealed that form alpha was more stable than form beta under any storage condition. A good linear relationship existed between the induction period and the transformation rate constant, irrespective of the storage conditions. The scanning electron photomicrographs of forms alpha and beta demonstrated that acicular crystals of form delta grew as the transformation progressed. This could be confirmed as the change in particle diameter of the samples.