Effect of compression temperature on the consolidation mechanism of chlorpropamide polymorphs

Raman spectroscopy of captopril crystals under low-temperature conditions

The polymorphism is a characteristic of several active principles, and can affect the bioavailability of a drug. Among the drugs used in the treatment of heart diseases, captopril is one of the most widely used in the world. Despite the knowledge of vibrational properties of captopril under high temperature and under high pressure, a lack of information impedes the understanding of the substance in the crystal form at low temperatures. In this research, we investigated the vibrational properties of captopril crystals under cryogenic conditions in the 300-8 K interval using Raman spectroscopy. By observing the behavior of the inter- and intra-molecular vibrations it was possible to infer that the captopril molecules suffered a rearranging into the unit cell due slight orientational changes mainly involving CH⋯O hydrogen bonds. The phenomenon occurs in a large temperature range. However, the observed changes do not suggest the occurrence of a structural phase transition and the Raman spectra indicate that the trans conformation is recorded down to the lowest temperature available in the experiments.

Real-time monitoring of pharmaceutical properties of medical tablets during direct tableting process by hybrid tableting process parameter-time profiles

BACKGROUND

Real-time monitoring is required for the pharmaceutical manufacturing process to produce high-quality pharmaceutical products.

OBJECTIVE

Changes in the critical tableting process parameters of single-punch tableting machine due to variability in the moisture content of the raw powders were monitored by hybrid tableting pressure-time profiles.

METHODS

After mixing of the raw powders, which consisted of theophylline, anhydrous lactose, potato starch and crystalline cellulose, they were stored at 0%, 45%, or 75% relative humidity (RH) for 24 h, respectively. Continuous tablet productions were carried out using the mixed powder samples at 10%, 45%, or 75% RH, respectively. The critical process parameters, such as upper and lower puncture pressures, die wall pressures, and inter-punch distances were recoded with the tableting machine, and then, tablet hardness (H), weight (W) and disintegration time (DT) of the tablets were measured.

RESULTS

Hybrid tableting pressure-time profiles were obtained from various critical process parameters, and calibration models to predict pharmaceutical properties were calculated based on the hybrid profiles using a partial-least-squares regression (PLSR) method. In addition, the consistency of the calibration models were verified by constructing robust calibration models.

CONCLUSION

Informetrical analysis for tablets based on hybrid tableting pressure-time profiles could evaluate the change of tablet properties dependent on the moisture content in the raw powders during the tableting process. The changes of tableting properties and elasticity were caused by agglomeration of powder particles at moisture content.

Pharmaceutical cocrystals, salts and polymorphs: Advanced characterization techniques

The main goal of a novel drug development is to obtain it with optimal physiochemical, pharmaceutical and biological properties. Pharmaceutical companies and scientists modify active pharmaceutical ingredients (APIs), which often are cocrystals, salts or carefully selected polymorphs, to improve the properties of a parent drug. To find the best form of a drug, various advanced characterization methods should be used. In this review, we have described such analytical methods, dedicated to solid drug forms. Thus, diffraction, spectroscopic, thermal and also pharmaceutical characterization methods are discussed. They all are necessary to study a solid API in its intrinsic complexity from bulk down to the molecular level, gain information on its structure, properties, purity and possible transformations, and make the characterization efficient, comprehensive and complete. Furthermore, these methods can be used to monitor and investigate physical processes, involved in the drug development, in situ and in real time. The main aim of this paper is to gather information on the current advancements in the analytical methods and highlight their pharmaceutical relevance.

High-pressure diffraction studies of molecular organic solids. A personal view

This paper discusses the trends in the experimental studies of molecular organic solids at high pressures by diffraction techniques. Crystallization of liquids, crystallization from solutions and solid-state transformations are considered. Special attention is paid to the high-pressure studies of pharmaceuticals and of biomimetics.

Effect of pressure up to 5.5GPa on dry powder samples of chlorpropamide form-A

The effect of pressure up to 5.5GPa on a dry powder sample of chlorpropamide (4-chloro-N-((propylamino)-carbonyl)-benzenesulfonamide), form-A (sp. gr. P2(1)2(1)2(1), a=9.066A, b=5.218A, c=26.604A), was studied in situ in a Merrill-Bassett diamond anvil cell using high-resolution X-ray powder diffraction (a synchrotron radiation source at SNBL ESRF, Grenoble). No evidence of the polymorphic transformation of chlorpropamide form-A to form-C was observed. The A-C polymorphic transition on tabletting previously reported by is therefore likely to be due to local heating effects. Similarly, the phase transitions of form-A reported by to be induced by pressure applied to a sample in its saturated ethanol solution (at 0.9 and at 2.0GPa) would appear to be solvent-mediated. In the dry sample, a phase transition may be supposed to occur at pressures above 4GPa, but this requires further studies.

Quantitative determination of polymorphic composition in intact compacts by parallel-beam X-ray powder diffractometry II. Data correction for analysis of phase transformations as a function of pressure

An analytical, non-destructive method using parallel-beam transmission powder X-ray diffractometry (PXRD) is presented for in situ whole compact detection and quantification of solid-state phase transformations in powder compacts. Accurate quantification of analyte in intact compacts using PXRD requires a mathematical correction prior to interpolation of calibration data to account for sample differences that result as a function of pressure; namely, compact thickness and solid fraction. Chlorpropamide is examined as a model system, selected because of its susceptibility to polymorphic transformations when consolidated using moderately low pressures. The results indicate that quantification of the transformed phase of chlorpropamide without corrections for solid fraction and thickness, underestimates the extent of transformation by 2.4%. Although the magnitude of the correction for this particular system of polymorphs is small, more significant values are expected for other compounds, particularly those with sufficient compactibility to allow the formation of low solid fraction calibration samples.

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.

Crystal doping aided by rapid expansion of supercritical solutions

The purpose of this study was to test the utility of rapid expansion of supercritical solution (RESS) based cocrystallizations in inducing polymorph conversion and crystal disruption of chlorpropamide (CPD). CPD crystals were recrystallized by the RESS process utilizing supercritical carbon dioxide as the solvent. The supercritical region investigated for solute extraction ranged from 45 to 100 degrees C and 2000 to 8000 psi. While pure solute recrystallization formed stage I of these studies, stage II involved recrystallization of CPD in the presence of urea (model impurity). The composition, morphology, and crystallinity of the particles thus produced were characterized utilizing techniques such as microscopy, thermal analysis, x-ray powder diffractometry, and high-performance liquid chromatography. Also, comparative evaluation between RESS and evaporative crystallization from liquid solvents was performed. RESS recrystallizations of commercially available CPD (form A) resulted in polymorph conversion to metastable forms C and V, depending on the temperature and pressure of the recrystallizing solvent. Cocrystallization studies revealed the formation of eutectic mixtures and solid solutions of CPD + urea. Formation of the solid solutions resulted in the crystal disruption of CPD and subsequent amorphous conversion at urea levels higher than 40% wt/wt. Consistent with these results were the reductions in melting point (up to 9 degrees C) and in the DeltaH(f) values of CPD (up to 50%). Scanning electron microscopy revealed a particle size reduction of up to an order of magnitude upon RESS processing. Unlike RESS, recrystallizations from liquid organic solvents lacked the ability to affect polymorphic conversions. Also, the incorporation of urea into the lattice of CPD was found to be inadequate. In providing the ability to control both the particle and crystal morphologies of active pharmaceutical ingredients, RESS proved potentially advantageous to crystal engineering. Rapid crystallization kinetics were found vital in making RESS-based doping superior to conventional solvent-based cocrystallizations.

Theoretical approaches to physical transformations of active pharmaceutical ingredients during manufacturing processes

Processing-induced transformations (PITs) during pharmaceutical manufacturing are well known but difficult to predict and often difficult to control. This review of the concepts of transformations is couched in terms of the issues associated with identifying rate-controlling events from the materials side and the processing side. Specifically, the approach is reconciling the characteristic time scale of the structural change(s) in the material with the time scale of the processing-induced stress. This is definitely a model (or rather a melding of a group of existing theories) in development. This overview is a 'snapshot' of the authors' attempts to identify the categories of existing theories needed to encompass all of the relevant events for each possible PIT. The ultimate goal is to establish a framework of concepts and theories for consideration, discussion, and modeling of PITs as well as to locate much of the relevant literature in the framework.

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.

Effects of crystalline form on the tableting compression mechanism of phenobarbital polymorphs

The effects of the polymorphic form on the compression mechanism of forms A, B, and F of phenobarbital were investigated using a compression simulator, mercury porosimetry, X-ray diffraction analysis, BET gas absorption method, and scanning electron microscopic (SEM) photography. The order of tablet hardness obtained from all phenobarbital polymorphs was form A > form B > form F in accordance with that of the specific surface area. The Cooper and Eaton method was applied to evaluate two individual compression processes: particle rearrangement (phase I) and fragmentation and/or deformation (phase II). The parameters for compression processes were calculated using a nonlinear regression analyses program, and the compression energies of phases I and II were calculated from these parameters. The relationship between specific surface area after compression and compression energy at phase I showed a good linear correlation, but their ratio did not. In contrast, the specific surface area ratio showed a linear relationship with the compression energy on phase II, but again the ratio of these two parameters did not. The tablet hardness showed a linear relationship with the specific surface area ratio, but not with the specific surface area. Again, the ratio of these two parameters did not show a linear relationship.