Effects of temperature and pressure during compression on polymorphic transformation and crushing strength of chlorpropamide tablets

[Advances in Pharmaceutical Manufacturing Process Management -From Physical Pharmaceutics to Automatic Pharmaceutical Production]

Since entering graduate school 43 years ago, I have been studying physical pharmaceutics with a focus on the effects of environmental factors on pharmaceutical properties of solid oral dosage forms during the manufacturing process. I have reported on changes in the characteristics of pharmaceutical products during manufacturing processes, such as grinding, mixing, granulation, and tableting owing to complicated phenomena based on chemical reactions or the crystalline polymorphic transitions of bulk drugs and excipients. To develop modern pharmaceutical manufacturing processes based on process analysis technology (PAT) as a next generation good manufacturing practice, real-time monitoring was introduced in these processes using a non-destructive analytical method, such as the near-infrared spectroscopy combined with chemometrics. Many case studies related to the mixing, granulation, tableting, and coating processes involving PAT have been reported. In those studies, I focused on clarifying the physical and chemical mechanism through "design space" representation. Additionally, non-destructive analytical methods, including X-ray computed tomography, audible acoustic emission, Raman spectroscopy, terahertz spectroscopy, and infrared thermal imaging analysis were applied as novel candidate analytical methods to the pharmaceutical process to monitor critical quality attributes. To achieve this purpose in various pharmaceutical dosage forms, I have been attempting the assembly of a modern manufacturing process managed through a "design space" paradigm involving in-line monitoring using novel analytical methods, multivariate analyses, and feed-back systems.

Modulation of the powder properties of lamotrigine by crystal forms

The mechanical properties of powders determine the ease of manufacture and ultimately the quality of the oral solid dosage forms. Although poor mechanical properties of an active pharmaceutical ingredient (API) can be mitigated by using suitable excipients in a formulation, the effectiveness of that approach is limited for high dose drugs or multidrug tablets. In this context, improving the mechanical properties of the APIs through solid form optimisation is a good strategy to address such a challenge. This work explores the powder and tableting properties of various lamotrigine (LAM) solid forms with the aim to facilitate direct compression by overcoming the poor tabletability of LAM. The two drug-drug crystals of LAM with nicotinamide and valproic acid demonstrate superior flowability and tabletability over LAM. The improved powder properties are rationalised by structure analysis using energy framework, scanning electron microscopy, and Heckel analysis.

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.

Development of spray-dried co-precipitate of amorphous celecoxib containing storage and compression stabilizers

The purpose of this study was to obtain an amorphous system with minimum unit operations that will prevent recrystallization of amorphous drugs since preparation, during processing (compression) and further storage. Amorphous celecoxib, solid dispersion (SD) of celecoxib with polyvinyl pyrrollidone (PVP) and co-precipitate with PVP and carrageenan (CAR) in different ratios were prepared by the spray drying technique and compressed into tablets. Saturation solubility and dissolution studies were performed to differentiate performance after processing. Differential scanning calorimetry and X-ray powder difraction revealed the amorphous form of celecoxib, whereas infrared spectroscopy revealed hydrogen bonding between celecoxib and PVP. The dissolution profile of the solid dispersion and co-precipitate improved compared to celecoxib and amorphous celecoxib. Amorphous celecoxib was not stable on storage whereas the solid dispersion and co-precipitate powders were stable for 3 months. Tablets of the solid dispersion of celecoxib with PVP and physical mixture with PVP and carrageenan showed better resistance to recrystallization than amorphous celecoxib during compression but recrystallized on storage. However, tablets of co-precipitate with PVP and carageenan showed no evidence of crystallinity during stability studies with comparable dissolution profiles. This extraordinary stability of spray-dried co-precipitate tablets may be attributed to the cushioning action provided by the viscoelastic polymer CAR and hydrogen bonding interaction between celecoxib and PVP. The present study demonstrates the synergistic effect of combining two types of stabilizers, PVP and CAR, on the stability of amorphous drug during compression and storage as compared to their effect when used alone.

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.

Polymorphic Transformation of Indomethacin Under High Pressures**The previous affiliation when this study was done, Organic Synthesis Research Laboratory, Sumitomo Chemical Co., Ltd. 3-1-98, Kasugade-naka, Konohana-ku, Osaka 554-8558, Japan

To study the effect of pressure on polymorphic transformation, intact powder, and ethanol slurry of alpha, gamma, and amorphous forms of indomethacin (IMC) were compressed under high pressures. A quantifying method for the percentages of these three constituents in sample powder was established. Using this method, analysis of compressed samples revealed that alpha form, which is difficult to prepare in stable form under atmospheric pressure, was easily obtained in stable form from the ethanol slurry of the amorphous IMC, which does not include any specific crystalline forms. In the ethanol slurry of gamma form, transformation to alpha form was observed: a reciprocal phenomenon under atmospheric pressure. These results can be rationally explained as follows: alpha form is more easily crystallized than gamma form in the ethanol solution, the more closely-packed crystal structure of alpha form is thermodynamically predominant over gamma form under high pressure, and pressure-induced amorphization occurs. This study indicates that crystallization experiments from the slurry of amorphous samples under various pressures can be useful in screening polymorphic or other solid states.

Depth Profiling of Compression-Induced Disorders and Polymorphic Transition on Tablet Surfaces with Grazing Incidence X-ray Diffraction

PURPOSE

The importance of induced crystal disorders like crystallite size, crystal defects, and amorphicity with respect to the dissolution rate of the drug has been discussed in many cases. Thus, the characterization of these properties is of great importance in the pharmaceutical formulation development, although the exact correlation between disorders and dissolution rate is still unclear. The aim of this study was to analyze pharmaceutical tablets with grazing incidence X-ray diffraction, which enables the depth profiling of the crystallographic properties of the tablets. To study and clarify the potential of grazing incidence diffraction in the analysis of pharmaceutical materials, the effect of the compaction process on the surface of tablets was examined.

METHODS

Carbamazepine, tolbutamide, and chlorpropamide tablets, compacted using different compression pressures, were studied using grazing incidence angle X-ray diffraction. The effects of compression on the crystallographic properties were investigated as a function of the distance from the tablet surface.

RESULTS

The surfaces of the tolbutamide and chlorpropamide tablets were disordered due to the compression. The manifestation of the disorder was deduced to be due to amorphicity, small crystallite size, and amount of crystal defects. The changes were mainly on the surface and diminished strongly as a function of the distance from the surface of the tablet. Moreover, the changes were dependent on the compression pressure used. The changes on the surface of the carbamazepine tablets were also due to the compression but these changes were not clearly dependent on the depth nor the compression pressure. The partial phase transition took place in the chlorpropamide tablets due to the compression. The magnitude of the transition was not highest on the surface because amorphization and texturization also took place on the tablet surface during the compression.

CONCLUSIONS

The present study proved that grazing incidence X-ray diffraction is a potential novel research tool to reveal crystallographic transformations taking place on the surfaces of the tablets induced, for example, by compression pressure.

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.

“Soft Tableting”: A New Concept to Tablet Pressure Sensitive Materials

The aim of this study was to confirm the hypothesis that tableting using excipients with greater elastic deformation results in improved performance of pressure-sensitive drugs relative to the excipients with low elastic deformation. Tableting with highly elastic deforming excipients and the resultant minimization of the process damage is referred to in this article as "soft tableting." Carrageenans, chitosans, and polyethylene oxides were tested as potentially useful tableting excipients. alpha-Amylase, amorphous indomethacin, theophylline monohydrate, and enteric-coated pellets were used as models for pressure-sensitive materials. Three-dimensional modeling of the tableting data and elastic recovery of the tablets were the tools for mechanical characterization. The crushing force of the tablets was analyzed. Inactivation of alpha-amylase was determined by using the starch iodine reaction method. Pseudopolymorphic and polymorphic changes were analyzed using Fourier transform (FT) Raman spectroscopy. The effects of pressure on the integrity of the pellets were tested by release studies and scanning electron microscopy. The process of tablet formation was characterized for potentially useful tableting excipients. The results were compared with the results of traditional excipients as microcrystalline cellulose (MCC), dicalcium phosphate dihydrate, and hydroxypropyl methylcellulose (HPMC). A ranking order for soft tableting was deduced from the mechanical properties. The tableting excipients were ranked according to their general plasticity (GP): GP(carrageenans)<GP(chitosans)<GP(MCC)<GP(HPMC)<GP(polyethylene oxides). This theoretical order of suitability has been experimentally proven to be valid for the pressure-sensitive materials. In conclusion, the new concept for soft tableting is valid.

Solid-state analysis of the active pharmaceutical ingredient in drug products

The solid form of a drug substance is important when developing a new chemical entity. The crystalline form used in development is significant based on possible manufacturability, solubility, bioavailability and stability differences between the solid forms. Regulatory issues require that the form present in a solid dosage form or liquids containing undissolved drug substance be identified. Drug product samples can be analyzed by a variety of techniques to determine the crystal form present or changes that occur during the manufacture of a drug product. The form present will affect development, regulatory and intellectual property issues.

Quantitative determination of polymorphic composition in intact compacts by parallel-beam X-ray powder diffractometry

This paper details the development of a method using parallel-beam X-ray powder diffractometry as a novel means of determining polymorphic composition in intact compacts. Two polymorphic systems, chlorpropamide and glycine, were selected. The polymorphic components were weighed, mixed, and compressed using a Carver press with 3/8-in. concave tooling. The compacts were then analyzed using parallel-beam X-ray powder diffractometry in transmission geometry. The data were processed using the profile-fitting module in the Shimadzu XRD-6000 software V 4.1 (for NT 4.0/98). The integrated intensity ratio of a selected peak for each crystal form was used for quantitation of each polymorph. Excellent linear correlation was observed for both polymorphic systems. The convex shape of the compact surface had no effect on the XRD patterns. Since parallel-beam X-ray diffractometry is not sensitive to the shape of the sample surface, it provides a simple method for quantifying polymorphs in intact compacts. Further work to extend this to formulated tablets is ongoing. The relatively larger variation in one of the peaks in the chlorpropamide study was found to be consistent with the computational analysis of the slip behavior of the stable polymorph. This method provides the first reported non-invasive X-ray diffraction pattern quantitation of crystal forms in intact compacts.

Moisture induced polymorphic transition of mannitol and its morphological transformation

The effects of moisture on the polymorphic transition of crystalline mannitol were investigated. Mannitol has three polymorphic forms, and was classified as alpha, beta, and delta form, respectively, by Walter-Lévy (C.R. Acad. Sc. Paris Ser. C (1968) 267, 1779). The water uptake of delta form crystalline was greater than that of the beta form when each crystalline form was stored at 97%RH (25 degrees C). The different powder X-ray diffraction patterns obtained before and after humidification confirmed that a moisture induced polymorphic transition from the delta to beta form had occurred. Morphological changes were also observed with an increase in the specific surface area of the delta sample from 0.4 to 2.3 m(2)/g being found on exposure to humidity. Thus it was suggested that the observed higher hygroscopicity of the newly formed beta form arose from the gradual increase in the surface area with the polymorphic transition from the delta to beta form. When considering the mechanism of this polymorphic transition, the results from molecular modelling, cross-polarisation/magic angle spinning (CP/MAS) solid-state NMR spectra and scanning electron-micrographs suggest that water molecules act as a molecular loosener to facilitate conversion from delta to the beta form as a result of multi-nucleation.

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.

The use of solution calorimetry with micellar solvent systems for the detection of polymorphism

The presence of multiple polymorphic forms in seven batches of raw material of a model compound having poor wettability properties (cimetidine) was studied by solution calorimetry. Due to the large number of polymorphic forms described in the literature ('Gazz. Chim. Ital., 109 (1979) 535'; 'J. Pharm. Sci., 73 (1983) 1436'; 'J. Pharm. Biomed. Anal., 3 (1985) 303') and its poor wettability characteristics, cimetidine was chosen as a model compound to illustrate the possible use of solution calorimetry in the detection of polymorphism using surfactant systems as solvents for dissolution. Due to the closeness of the melting points of the different polymorphic forms of cimetidine, DSC was not the best investigational tool. As initially suspected, the measurement of enthalpy of solution values in water of the cimetidine batches was not possible. However, the use of sodium dodecyl sulfate (SDS) and polysorbate 20 (Tween 20(R)) at concentrations above their respective cmc values permitted the detection of significant differences in enthalpy of solution among several batches. The presence of different polymorphic forms was confirmed by microscopy, X-ray powder diffractometry, and Fourier transform infrared spectroscopy.

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.

Polymorphism of clarithromycin

It is well recognized that physicochemical properties of drugs are affected by the type of polymorphic crystalline form of drugs. Clarithromycin is known to exist in at least three polymorphic crystalline forms. Since conventional means to obtain the most thermodynamically stable form (Form II) for the antibiotics is known to be associated with a low purity of the stable form, we developed a novel method to improve the purity of the crystalline form by a modification of the preparation process. The new method involved a simple recrystallization of clarithromycin in solvents having 5-12 carbon atoms (e.g., hexane and heptane) or ethers with 4-10 carbon atoms (e.g., isopropyl ether) and, thus, less likely to be associated with the problem in purity of resulting crystal. Differential scanning calorimetry and powder X-ray diffraction were used to compare the crystalline form of the resultant powder with Form II crystal prepared by the conventional method. The crystal prepared by the new method was identical to Form II crystal of the conventional method as evidenced by the lack of the exothermic peak near 110 degrees C in differential calorimetry scan, indicating that Form II crystal could be readily prepared by the new process. Therefore, these data indicated that the improvement in the purity of the Form II crystal for clarithromycin as well as a significant cost reduction is likely by the novel method.

Quantitation of cefepime.2HCl dihydrate in cefepime.2HCl monohydrate by diffuse reflectance IR and powder X-ray diffraction techniques

The identification, characterization and quantitation of crystal forms is becoming increasingly important within the pharmaceutical industry. Multi-disciplinary, physical analytical techniques are necessary for this task. In this work, diffuse reflectance mid-infrared (IR) and powder X-ray diffraction (XRD) analyses were used to identify two different hydrated forms of cefepime.2HCl, a cephalosporin. Characterization of the mono- and dihydrate forms led to separate IR and XRD quantitative assays for the determination of dihydrate content in cefepime.2HCl monohydrate bulk material. For the IR assay, a working range of 1.0-8% (w/w) was established with a minimum quantifiable level (MQL) of 1.0% (w/w) and a limit of detection (LD) of 0.3% (w/w) dihydrate in monohydrate material. The XRD assay displayed a working range of 2.5-15% (w/w) with an MQL of 2.5% (w/w) and an LD of 0.75% (w/w). Cross validation was performed between the two techniques, with a good correlation displayed for each assay as compared with the known concentrations and as compared with each other. In addition, a full evaluation of potential assay errors was made.

Effect of compression temperature on the consolidation mechanism of chlorpropamide polymorphs

The effect of environmental temperature on the compression mechanism of chlorpropamide (CPM) polymorph, forms A and C, was investigated with an eccentric type tabletting machine with two load cells and a noncontact displacement transducer. The temperature of the die was controlled at 0 and 45 degrees C by a thermocontroller. Sample powders (200 mg), which were also controlled at 0 and 45 degrees C by a thermocontroller, were compressed at almost 230 MPa. The tabletting dynamic processes of CPM forms A and C at 0 and 45 degrees C were evaluated by Cooper and modified Heckel analyses. The results suggest that particle brittleness or plasticity was affected by compression at different temperatures. The higher tablet hardness of form A at 45 degrees C was thought to be caused by the increased plasticity of primary particles, whereas that of form C at 45 degrees C was ascribed to the decreased size of the secondary particles.

The qualitative and quantitative analysis of chlorpropamide polymorphic mixtures by near-infrared Fourier transform Raman spectroscopy

We analyzed binary mixtures of polymorphs A and B of chlorpropamide ((1-[4-chlorobenzenesulphonyl]-3-propyl urea)) by near-infrared Fourier transform Raman spectroscopy (FTRS). The individual polymorphs were prepared and characterized by differential scanning calorimetry (DSC), Fourier transform infrared (FT-IR) microscopy, and physical appearance. The FTR spectra of the two polymorphs showed distinct differences which result from "crystal splitting" effects. A series of 13 different mixtures of polymorph A and B was prepared by geometric mixing and their FTR spectra statistically analysed by factor analysis programming. Predictions of the A/B polymorphic composition of mixtures were made and compared with the theoretical values. The results demonstrate that FTRS combined with factor analysis programming may be successfully applied to the in situ monitoring of the A/B polymorphic nature of a chlorpropamide sample.