Processing effects on crystallinity of cephalexin: Characterisation by vacuum microbalance

Modulating the dehydration conditions of adefovir dipivoxil dihydrate to obtain different physical forms of anhydrate

The physical form of anhydrous adefovir dipivoxil (AD), obtained following the dehydration of AD dihydrate, was governed by the kinetics of water removal. The rate and extent of water removal following the dehydration of AD dihydrate was manipulated by altering the sample size, pan configuration, and heating rate in a differential scanning calorimeter. Interestingly, when there was moderate resistance to water removal, a new anhydrous polymorph (melting point 80°C) was obtained. High resistance to water removal resulted in amorphous AD. Variable temperature XRD of AD provided direct and unambiguous evidence of this new polymorph. We have prepared and characterized this new anhydrous polymorph as well as amorphous AD. Based on HPLC, AD dihydrate heated under different conditions in the DSC was observed to be chemically stable. When exposed to water vapor (RH ≥ 80%; 25°C), the new polymorph had a stronger propensity to convert to AD dihydrate than the amorphous anhydrate or AD form I.

Unintended water mediated cocrystal formation in carbamazepine and aspirin tablets

The water of crystallization released during dehydration of dibasic calcium phosphate dihydrate (DCPD) mediated the cocrystal formation between carbamazepine (CBZ) and nicotinamide (NMA) in intact tablets. The dehydration of DCPD, the disappearance of the reactants (CBZ and NMA) and the appearance of the product (CBZ-NMA cocrystal) were simultaneously monitored by quantitative powder X-ray diffractometry. In a second model system, the water of crystallization released by the dehydration of DCPD caused the chemical decomposition of aspirin. Salicylic acid, one of the decomposition products, reacted with CBZ to form CBZ-salicylic acid cocrystal in tablets. This is the first report of cocrystal formation in intact tablets, demonstrating water mediated noncovalent synthesis in a multicomponent matrix. While the potential implications of such transformations, on both the mechanical and biopharmaceutical properties, can be profound, their characterization, using conventional solution based analytical techniques, can be challenging.

Advances in solid dosage form manufacturing technology

Currently, the pharmaceutical and healthcare industries are moving through a period of unparalleled change. Major multinational pharmaceutical companies are restructuring, consolidating, merging and more importantly critically assessing their competitiveness to ensure constant growth in an ever-more demanding market where the cost of developing novel products is continuously increasing. The pharmaceutical manufacturing processes currently in existence for the production of solid oral dosage forms are associated with significant disadvantages and in many instances provide many processing problems. Therefore, it is well accepted that there is an increasing need for alternative processes to dramatically improve powder processing, and more importantly to ensure that acceptable, reproducible solid dosage forms can be manufactured. Consequently, pharmaceutical companies are beginning to invest in innovative processes capable of producing solid dosage forms that better meet the needs of the patient while providing efficient manufacturing operations. This article discusses two emerging solid dosage form manufacturing technologies, namely hot-melt extrusion and fluidized hot-melt granulation.

Processing-Induced Phase Transitions of Theophylline—Implications on the Dissolution of Theophylline Tablets

Aqueous wet massing of stable anhydrous theophylline (A) with polyvinylpyrrolidone (PVP) resulted in its complete transformation to theophylline monohydrate (M). Drying at 45 degrees C, resulted in the formation of metastable anhydrous theophylline (A*) which then transformed to A. PVP, a known crystallization inhibitor, was effective in inhibiting the A* --> A transition. The higher molecular weight polymer, PVP K90, was more effective in inhibiting the A* --> A transition as compared to PVP K17. The disappearance of M, and the formation of A* and A was simultaneously monitored by XRD. An increase in the drying temperature from 45 to 55 degrees C accelerated the A* --> A transition. In granules prepared by the high-shear process, approximately 50% of theophylline existed as A and the rest as A*. In contrast, the fluid-bed granulation process yielded granules containing only A. Thus, the physical form of theophylline in tablets was influenced by the molecular weight of the binding agent, the granulation method, and the drying temperature. Using A as the starting material, tablets were manufactured by high-shear aqueous wet granulation process and the A* content was quantified. These tablets were stored under various relative humidity (RH) conditions at 25 degrees C for 2 weeks. Storage at RH >or= 33% caused complete A* --> A conversion accompanied by a pronounced decrease in the initial dissolution rate indicating that phase transitions during processing and storage can have a significant influence on product performance.

Interactions of water with the surfaces of crystal polymorphs

The purpose of this study is to investigate the interactions of water adsorption on the surfaces of different crystal forms of the same drug. The energy of interaction between water vapor and the surfaces of the two crystal polymorphs has been investigated as a function of temperature and water activity. One of the adsorbents, the metastable form of the monotropically related pair used here, showed greater adsorptive capacity in terms of both the amount of water uptake as well the integral heat of adsorption. However, the specific heat of adsorption values revealed that even though the surface of the thermodynamically stable crystal adsorbs less water, water molecules are actually more strongly bound when adsorbed on the surface of the stable crystal form. This means that the metastable crystal form adsorbs a greater amount of more weakly bound water. Conversely, the thermodynamically stable form, presents on its surface a smaller number of stronger adsorption sites for water. This study also shows that the crystalline character of the surfaces of the two polymorphs, shown as quantifiable differences in their surface interactions, is maintained despite the presence of any crystal defects incorporated upon milling.

Effect of water content on the solid-state stability in two isomorphic clathrates of cephalosporin: cefazolin sodium pentahydrate (alpha form) and FK041 hydrate

This study clearly demonstrates that clathrated water molecules can contribute to both chemical stabilization and destabilization of clathrates. The solid-state stabilities for two isomorphic clathrates of cephalosporin, cefazolin sodium and FK041, were investigated in terms of the effects of water content. The isomorphic ranges of water content were estimated to be 3.5-5 mol/mol for alpha-form cefazolin sodium and 2-4 mol/mol for FK041 hydrate. Upon the isomorphic dehydration, alpha-form cefazolin sodium was destabilized as the water content decreased below 4.25 mol/mol owing to the disruption of hydrogen bonding network in lattice channels. In this case, the hydration of clathrated water up to 4.25 mol/mol contributed to the physical and chemical stability of the crystals. On the contrary, the isomorphic hydration in FK041 hydrate contributed to the chemical destabilization owing to the high water activity. The difference in water activity between alpha-form cefazolin sodium and FK041 hydrate could be attributed to the size of water channels.

Water vapor adsorption properties of amorphous cefditoren pivoxil evaluated by adsorption isotherms and microcalorimetry

Water vapor adsorption of ground cefditoren pivoxil was studied. The amount of water adsorbed increased with a decrease in the crystallinity of cefditoren pivoxil. It was found from the microcalorimetric measurements that the differential heat of water vapor adsorption at 1.5% adsorbed water increased with decreasing crystallinity of cefditoren pivoxil, suggesting that hygroscopicity of cefditoren pivoxil was enhanced by grinding. These results indicated that hydrophilic adsorption sites in cefditoren pivoxil increased through the grinding process. The results of infrared (IR) spectra examination suggested that the increment of hydrophilic adsorption sites through the grinding process resulted from the change of the environment of the carbonyl groups in two esters and amide.

Change of the microstructure of microcrystalline cellulose with grinding and compression

The microstructure of microcrystalline cellulose was investigated by use of a radial distribution function (RDF) based on the intensity of X-ray scattering data. Changes in the microstructure of the cellulose as a result of grinding and compression were detected by use of the RDF. The RDF of intact microcrystalline cellulose had peak maxima corresponding to distances of approximately 1.5, 2.6, 5.0, 8.2, 13.3 and 17.0 A. The first two corresponded to the intramolecular atomic distances; other peaks were attributable to the intermolecular (inter-fibre) atomic distance. Changes in the RDF as a result of grinding indicated that the regular intermolecular atomic arrangement was gradually lost. Compression resulted in formation of long-range (> 20 A) ordering of the intermolecular (inter-fibre) atomic arrangement. These results show that RDF analysis is suitable for monitoring changes in the structure of microcrystalline cellulose which occur as a result of grinding and compression.

Moisture-dependent crystallization of amorphous lamotrigine mesylate

A commercially available computer-controlled vacuum moisture balance was used for determining moisture sorption isotherms of freeze-dried and spray-dried lamotrigine mesylate drug substance and freeze dried drug product containing mannitol. The presence or absence of desorption hysteresis and the characteristics of the weight-versus-time profile as a sample was exposed to a defined relative humidity ramp were sensitive indicators of moisture-induced crystallization. Combination of the moisture sorption data with polarized light microscopy, differential scanning calorimetry, and X-ray powder diffraction provided qualitative verification of the crystallization with < 50 mg of sample. The normalized water loss during crystallization was used to detect as little as 2% amorphous content in physical mixtures of amorphous and crystalline lamotrigine mesylate. Moisture sorption, water plasticization, and crystallization properties of amorphous forms prepared by spray drying and freeze drying were nearly identical. Cofreeze-drying lamotrigine mesylate with D-mannitol resulted in a mixture of amorphous lamotrigine mesylate with properties similar to those of spray-dried or freeze-dried materials and crystalline D-mannitol. The amount of water needed for crystallization over a time scale observable in the moisture balance was considerably more than the amount needed to lower the glass transition temperature of the sample to the operating temperature of the instrument. This result illustrated the importance of time scale effects in determining critical moisture levels for crystallization from the amorphous state.