Changes in solid-state structure of cyclophosphamide monohydrate induced by mechanical treatment and storage

Crystallization of Cyclophosphamide Monohydrate During Lyophilization

The purpose of this study was to investigate the phase behavior of cyclophosphamide (CPA) during various stages of lyophilization, with special emphasis on obtaining crystalline CPA monohydrate (CPA-MH) in the lyophilized product. Subambient differential scanning calorimetry and low-temperature X-ray diffractometry (LTXRD) were used to study the phase behavior of CPA solution (3.7% w/v). In situ lyophilization in LTXRD chamber was used to monitor the phase transitions occurring during the drying stages. Finally, the implications of these findings were confirmed by freeze-drying the aqueous solution in a laboratory-scale freeze-dryer. The results suggested that CPA remains amorphous during freeze concentration, with a T_g' of -50°C. However, its crystallization as CPA-MH can be induced by annealing the frozen solution between -5°C and -10°C. In situ lyophilization in LTXRD showed that the CPA-MH crystallized during annealing, rapidly dehydrated during primary drying, thereby causing structural collapse. The dehydration of CPA-MH can be prevented by lowering the escaping tendency of water molecules from the crystal lattice of CPA-MH by maintaining the chamber pressure to 300, 400, or 500 mTorr. This study highlights the relationship of process parameters used during lyophilization with the solid form of lyophilized CPA.

Physical characterization of TRK-720 hydrate, the very late antigen-4 (VLA-4) inhibitor, as a solid form for inhalation: preparation of the hydrate by solvent exchange among its solvates and mechanistical considerations

TRK-720 has been under development as a dry powder inhaler (DPI) for treating bronchial asthma. DPI is a drug formulation of an active pharmaceutical ingredient (API) supported by carrier particles. On inhalation, the API particles dissociate from the carriers through physical stimulation and reach the lung through the humid upper airways, therefore, the API has to remain physically and chemically stable despite contact with carriers and low relative humidity. Also it should be pulverized into an appropriate size (1-10 microm) for reaching the target region. To fulfill these requirements, API in crystal form is needed. Polymorphic screening using 42 solvents produced 9 solvates but not the target hydrate or ansolvate crystal. When the solvent was removed from each solvate, only methanolate could reproducibly be converted into hydrate by water vapor substitution. As the hydrate satisfied the above requirements for DPI, it was selected as a solid form for development. Also, the results of single crystal X-ray structural analyses and calculations of crystal packing energies, for five of the solvates, indicated that only the methanolate can be converted into the hydrate through solvent substitution.

An insight into water of crystallization during processing using vibrational spectroscopy

Many organic molecules used as drugs can incorporate water into their crystal lattice. These compounds are also prone to processing-induced transformations (PITs) because processing often exposes the compounds to moisture, heat and mechanical stress. The aim of this review is to provide an overview of the possibilities for following and understanding hydrate/anhydrate transformations using vibrational spectroscopy (mid-infrared, near-infrared, Raman and terahertz). The review begins with a general section on hydrates, followed by considerations on the impact of these on drug products and a description of transformation mechanisms of hydrates. Moreover, a general introduction is given for the spectroscopic techniques together with a discussion of critical issues for quantification models. Unit operations that may induce transformations in hydrate systems are discussed with focus on the published work on the use of spectroscopy to derive information from these processes. Finally, the effect of excipients on PITs is discussed.

Effect of Processing on Celecoxib and Its Solvates

Pharmaceuticals mostly exist in crystalline form and exhibit the phenomenon of differential crystal packing and configurational arrangements of molecules, called polymorphism. Pharmaceutical processing by introducing significant amount of stress alters the molecular interactions in the system engendering polymorphic transformations. The energy supplied by these processing steps tends to overcome the energy barriers between different solid-state forms, thus yielding undesirable changes in the physicochemical and material characteristics of drugs or their dosage forms. Therefore, the role of these unit processes in solid-state transformations must be cautiously studied and if required appropriate controls should be used to monitor such events. The present study was aimed at studying the effect of major energy imparting pharmaceutical unit processes, like size reduction, wet granulation, consolidation, and compression on solid-state transformation of Celecoxib, a selective cyclooxygenase-II inhibitor and its N,N-dimethyl acetamide and N,N-dimethyl formamide solvated forms. A qualitative estimation of crystal transformation in processed samples was performed using DSC, microscopy, FTIR spectroscopy, and XRPD. FTIR was also applied for the development of a quantification method to find the percentage of transformation in N,N-dimethyl acetamide solvated form during compression.

Effects of mechanical processing on phase composition

One factor that must be considered during drug development process is that various types of pharmaceutical manufacturing can alter the physical characteristics of the drug entity. These effects become particularly important during scale-up of processing operations, because new and unanticipated results can become manifest in systems of insufficient characterization. Any transformed drug substance or altered dosage form could exhibit an altered solubility or dissolution rate that might produce an undesirable bioavailability profile. Some of the more interesting mechanical manipulations that have the potential to yield problems include particle size reduction and compression, and such investigations are the focus of this minireview.

Dynamic solid-state and tableting properties of four theophylline forms

Relationships between solid-state, densification and compact properties of theophylline monohydrate (TMO), a mixture of forms (TMIX), and anhydrous polymorphs I (TA-I) and II (TA-II) were evaluated. Solid-state identification of powders and compacts was accomplished by powder X-ray diffraction. A compaction simulator was used to assess deformation behaviour of the powders and to prepare compacts. Porosity and tensile strength of the compacts were determined after 1,24, and 168 h of storage at 22% relative humidity. TA-II was stable, whereas TA-I, TMIX and TMO partially transformed to the TA-II form during storage. All theophylline modifications primarily deformed by plastic flow. Increased water content decreased resistance towards densification and deformation of TMIX and TMO when compared to TA-II or TA-I, demonstrating viscoelasticity. Permanent densification behaviours of TMIX and TMO approached to that of TA-II during storage. Tensile strength of the different theophylline forms were practically equal after 1 h of storage. Tensile strength and porosity of TMIX and TMO compacts increased during the storage. Dynamic solid-state transformations from TMO, TMIX and TA-I to TA-II were associated with parallel changes in their densification and compact properties. The extent of these changes was also dependent on the materials' water content.

Physical characterization of picotamide monohydrate and anhydrous picotamide

Picotamide is an antiplatelet agent given by mouth as monohydrate (PICOW) (Plactidil) in thrombo-embolic disorders. This study deals with physical characterization of PICOW recrystallized from various solvents and the respective dehydration products using X-ray powder diffractometry (XRD), infrared spectroscopy (IR), and thermal analytical techniques (differential scanning calorimetry, DSC; thermogravimetric analysis, TGA; simultaneous TGA/DSC; hot stage microscopy, HSM). Monophasic and biphasic DSC and TGA profiles of water loss were recorded under open conditions for PICOW samples which showed the same monoclinic crystal structure. Biphasic profiles became monophasic for gently ground samples which were, however, structurally identical to the intact samples. Morphological factors, the various degree of "perfection" of the PICOW crystal lattice, and/or cluster aggregation of PICOW crystals were assumed to be responsible for the differing dehydration patterns. Polymorphism in anhydrous picotamide, i.e., nucleation of crystal forms A, mp 135.5 +/- 0.4 degrees C, and B, mp 152.9 +/- 0.3 degrees C after dehydration of PICOW, was detected by DSC and HSM. The dehydration product of PICOW under isothermal conditions (115 degrees C, 20 mmHg), PICOA, was mainly composed of the lower melting polymorph A (fusion enthalpy 74.4 +/- 2.2 J g(-1)), which gradually reverted to the starting hydrate by storing in an ambient atmosphere. Dissolution tests of PICOW and PICOA in water at 37 degrees C as both powders and compressed disks reflected to some extent the higher solubility of the metastable form (by 24% at 37 degrees C) in terms of both higher dissolution efficiency and percent of active ingredient dissolved (by 28%) and intrinsic dissolution rate (by 32%).

Polymorphism in anhydrous theophylline--implications on the dissolution rate of theophylline tablets

The objects of this investigation were (i) to prepare and characterize a new anhydrous theophylline phase that is metastable under ambient conditions, and (ii) to prepare model tablet formulations containing either this metastable anhydrate (I*) or stable anhydrous theophylline (I), store them under different relative humidity (RH) conditions, and compare their dissolution behavior. I* was prepared by dehydration of theophylline monohydrate (II). Variable temperature X-ray powder diffractometry of II revealed the following series of transitions: II-->I*-->I. The metastable anhydrate, I*, which has not yet been reported in the literature, appears to be related monotropically to I. It was characterized by ambient and variable temperature X-ray powder diffractometry, Karl Fischer titrimetry, and thermoanalytical techniques (differential scanning calorimetry and thermogravimetric analysis). Tablet formulations containing either I* or I were prepared and stored at 33 and 52% RH (room temperature). The solid state of the drug was monitored by X-ray powder diffractometry and the tablets were subjected to the USP dissolution test. In tablets, I* completely converted to I in < or = 10 days when stored at either 33 or 52% RH. Scanning electron microscopy provided direct visual evidence of recrystallization. This recrystallization was accompanied by a decrease in the dissolution rate of the stored formulations that was so pronounced in the formulations stored at 52% RH that they failed the USP dissolution test. The in situ solid-state transition appears to be responsible for the decrease in dissolution rate observed following storage. Stored tablets containing I showed neither a phase transition nor an alteration in their dissolution behavior.

Effects of grinding and humidification on the transformation of conglomerate to racemic compound in optically active drugs

The effects of grinding and humidification on the transformation of conglomerate to racemic compound have been investigated by X-ray powder diffraction (XPD), differential scanning calorimetry (DSC) and infrared (IR) spectroscopy for leucine, norleucine, valine, serine, tartaric acid and malic acid. Racemic physical mixtures were prepared by physical mixing of equimolar quantities of D and I. crystals using a mortar and pestle. Ground mixtures were obtained by grinding the physical mixtures with a vibrational mill. Humidification was performed by storing the physical mixtures and the ground mixtures in a desiccator containing saturated aqueous salt solutions at 40 degrees C. When physical mixtures of malic acid, tartaric acid and serine were ground, the XPD peaks of the racemic compounds were observed. The XPD patterns of humidified physical mixtures of these compounds also showed the formation of the racemic compounds. This indicated that grinding or humidification of malic acid, tartaric acid and serine induced the transformation of conglomerate to racemic compound crystals. When, on the other hand, the physical mixtures of valine, leucine and norleucine were ground, peaks of racemic compounds were not detected in the XPD pattern. After humidification of the ground mixtures of valine, leucine and norleucine, however, the XPD peaks of racemic compounds were observed. DSC and IR studies revealed consistent results. We concluded that grinding or humidification of malic acid, tartaric acid and serine could induce the transformation of a conglomerate to racemic compound. In contrast, humidifying after grinding was needed to bring about the transformation in leucine, norleucine and valine.