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ABSTRACT: For efficient and effective drug development it is desirable to acquire a deep understanding of the dissolution behaviour of potential candidate drugs and their physical forms as early as possible and with the limited amounts of material that are available at that time. Using 3-10mg sample quantities, the ability of a UV imaging system is investigated to provide deep mechanistic insight into the intrinsic dissolution profiling of a range of compounds and physical forms assessed under flow conditions. Physical forms of indomethacin, theophylline and ibuprofen were compressed and their solid-state form confirmed before and after compression with X-ray methods and/or Raman spectroscopy. Intrinsic dissolution rates (IDRs) were determined using the compact's UV-imaging profile. The ratio in the IDRs for theophylline anhydrate over hydrate was 2.1 and the ratio for the alpha form of indomethacin over the gamma form was approximately 1.7. The discriminatory power of the novel UV area visualisation approach was shown to be high in that process-induced solid-state dissolution differences post-micronisation could be detected. Additionally, the scale-down system was able to visualise a previously observed increase in ibuprofen IDR with an increase in concentration of sodium dodecyl sulphate. The mechanistic dissolution insights from the visualisation approach are evident.
International journal of pharmaceutics 05/2012; 434(1-2):133-9. · 2.96 Impact Factor
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ABSTRACT: To evaluate Taylor dispersion analysis (TDA) as a novel method for determination of hydrodynamic radius of therapeutic peptides and proteins in non-stressed and stressed formulations and to compare it with dynamic light scattering (DLS).
The hydrodynamic radius of oxytocin, bovine serum albumin, various monoclonal antibodies (type IgG) and etanercept at concentrations between 0.05 and 50 mg/ml was determined by TDA and DLS. IgGs and etanercept were stressed (elevated temperatures) and analyzed by TDA, DLS and HP-SEC.
TDA and DLS were comparable in sizing non-stressed peptides and proteins in a concentration range of about 0.5 to 50 mg/ml. TDA performed well even at lower concentrations, where DLS tends to provide theoretically high values of the Z-average radius. However, because of differences in the detection physics, DLS was more weighted towards the detection of aggregates in stressed formulations than TDA. Advantageously, TDA was also able to size the small peptide oxytocin, which was not feasible by DLS.
TDA allows the accurate determination of the hydrodynamic radius of peptides and proteins over a wide concentration range, with little interference from excipients present in the sample. It is marginally less sensitive than DLS in detecting size increase for stressed protein samples.
Pharmaceutical Research 05/2011; 28(9):2302-10. · 4.09 Impact Factor
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ABSTRACT: The escalating number of new therapeutic biopharmaceuticals being developed and their high value increases the need for the development of novel analytical technologies. Faster analysis time, high accuracy, low sample consumption and the ability to monitor process flow are all essential prerequisites. We evaluate a novel analytical instrument that combines UV area imaging and Taylor dispersion analysis (TDA) to determine the hydrodynamic radius of proteins and small molecules in solution. Benchmarking the results against dynamic light scattering, we report the influence of injection system, injection volume, flow rates, analyte concentration and highlight the importance of washing procedures. Issues arising from the manual injection valve in the alpha laboratory system that led to high standard deviations were eliminated by incorporating an automated injector in a beta system. The hydrodynamic radii obtained show good correlation with literature values and in most cases a relative standard deviation of less than 5%. The system is fully automated after coupling to the CE which allows for multiple injections and sample/buffer changes without operator intervention. The small sample size (approx. 60 nL), the lack of sample preparation required, and the speed of analysis (approx. 2-3 mins) makes this instrument highly applicable to the real-time analysis of inherently unstable, high cost biopharmaceutical materials where understanding their aggregation state and size is important.
International journal of pharmaceutics 03/2011; 411(1-2):64-8. · 2.96 Impact Factor
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ABSTRACT: The stabilizing ability of the excipient on pharmaceutically relevant proteins for potential therapeutic use is an extensive area of research but the effect the protein has on the excipient is rarely reported. The influence of two model proteins on the polymorphic behaviour of mannitol during spray drying was therefore investigated. Spray dried mannitol/protein blends were characterised structurally using X-ray powder diffraction (XRPD) and Fourier transform Raman spectroscopy (FT-Raman) and thermally by differential scanning calorimetry (DSC) and also thermogravimetric analysis (TGA). To assess the long term storage stability, samples were subjected to conditions of elevated temperature and relative humidity (RH). Structural and thermal analysis of the samples showed that upon spray drying mannitol could be completely amorphous or crystalline dependent on the protein co-spray dried. Upon storage at elevated temperature and RH different polymorphic forms of mannitol (beta and delta) were evident again dependent on the protein co-spray dried. Under the conditions employed there was a polymorph directing effect on mannitol dependent on the protein with which it was co-spray dried with co-solute effects on relative water levels being indicated as a major factor in directing the polymorph.
International journal of pharmaceutics 09/2009; 382(1-2):67-72. · 2.96 Impact Factor
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ABSTRACT: Following the production of spray-dried mannitol powders, it is essential that the polymorphic content of each individual product is completely characterized. The implications of the polymorphic behavior of mannitol are immense. The appearance or disappearance of a crystalline form within a dosage form can have costly repercussions and lead to a dosage form being withdrawn.
In this study, commercially available and laboratory-produced spray-dried mannitol products were characterized to establish the polymorphic content of each. Their polymorphic behavior was also characterized after laboratory scale pharmaceutical processes. Thermal analysis employed differential scanning calorimetry, thermogravimetric analysis, and isothermal microcalorimetry. Structural analysis of the samples was obtained using X-ray powder diffraction and Fourier transform Raman spectroscopy.
Structural analysis revealed that alpha- and beta- polymorphic forms were present in the commercial samples and some contained a mixture of polymorphs. Reprocessing employing spray drying indicated alpha- to beta- polymorphic transitions occurred within some of the samples.
It is essential that preformulation studies where spray-dried mannitol products are to be employed must take into account its polymorphic behavior upon supply, processing, and subsequent storage.
Drug Development and Industrial Pharmacy 07/2009; 35(6):712-8. · 1.49 Impact Factor
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ABSTRACT: The inherent instability of proteins when isolated from their native conditions creates the necessity of suitable stabilisation techniques. Because of the instability of proteins in solution it is often necessary to produce them as solid formulations. A method of producing relatively stable, solid protein pharmaceuticals is to incorporate them with a suitable excipient into an amorphous matrix by dehydration. The use of spray dried multiple excipient/single protein blends was compared to single excipient/protein systems using lysozyme as a model protein to establish the stabilising ability of such systems. Unprocessed controls and spray dried samples were characterised structurally by X-ray powder diffraction and Fourier transform Raman spectroscopy and also thermally by differential scanning calorimetry and thermogravimetric analysis. Retained lysozyme activity was assayed enzymatically. To assess long-term stability, samples were subjected to conditions of elevated temperature and relative humidity (RH) 40 degrees C/75% RH. Structural and thermal analysis of samples revealed that mannitol/trehalose spray dried excipient/lysozyme blends were completely amorphous upon production but partially recrystallised upon storage at elevated temperature and RH. Biological activity assays revealed that samples containing trehalose retained the highest percentage activity. Under the conditions employed mannitol/trehalose systems stabilise lysozyme more effectively than single excipient systems due to their ability to form amorphous products.
European Journal of Pharmaceutical Sciences 04/2008; 33(3):294-305. · 3.21 Impact Factor
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ABSTRACT: The production of stable protein formulations is difficult due to unique properties of proteins. Accordingly, spray drying and crystallisation techniques were assessed for their effects on trypsin, a model protein. Samples were investigated using polarising microscopy, thermogravimetry, differential scanning calorimetry (DSC), FT-Raman spectroscopy and enzymatic assay. Unprocessed, spray-dried and crystallised trypsin were evaluated in solution for secondary structure in low and high protein concentrations using aqueous state FT-Raman spectroscopy and for folding reversibility employing high sensitivity differential scanning calorimetry. Spray-dried trypsin showed FT-Raman spectral changes and less biological activity, after rehydration, compared with unprocessed and crystallised trypsin. Crystals maintained activity better than did the spray-dried form and retained a higher folding reversibility compared to unprocessed and spray-dried protein. Proteins may denature with structural changes under thermal stress and lose their activities. Thus, this research studied the effect of heating solid unprocessed, spray-dried and crystallised trypsin samples on their secondary structures, using FT-Raman spectroscopy, to identify the influence of the initial solid form on its propensity for thermal denaturation and whether this can be correlated with catalytic activity. DSC heated protein samples to two temperatures, one before the apparent denaturation temperature (T(m)) and the other after the T(m). Samples heated below their T(m) showed some perturbations of the secondary structure and some activity, whilst materials rose to the higher temperature were insoluble with complete loss of activity.
European Journal of Pharmaceutical Sciences 04/2007; 30(3-4):315-23. · 3.21 Impact Factor
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ABSTRACT: Microcrystalline cellulose (MCC) and cross-linked polyvinylpyrrolidone (PVP-CL) were examined as polymeric carriers to support amorphous ibuprofen (IB). Drug/carrier systems were prepared as physical mixes, and drug was loaded onto the polymers by hot mix and solvent deposition methods. The systems were examined using differential scanning calorimetry (DSC), X-ray powder diffractometry (XRD) and by dissolution testing. PVP-CL reduced drug crystallinity more than MCC and, surprisingly, even very simple mixing of ibuprofen with PVP-CL induced disordering of the drug. Increased ibuprofen dissolution rates were achieved with both polymers, in the order of solvent deposition>hot mixes>physical mixes. The increased dissolution rates could be attributed to a combination of faster dissolution from amorphous ibuprofen, microcrystalline drug deposition on carrier surfaces and polymer swelling. However, no clear relationship was observed between ibuprofen dissolution rates (using first order, Higuchi or Hixson-Crowell relationships) and drug crystallinity.
European Journal of Pharmaceutical Sciences 11/2005; 26(3-4):288-94. · 3.21 Impact Factor
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ABSTRACT: Moisture and temperature promote protein degradation. The stabilities of commercial, crystallised and spray-dried lysozyme, a model protein, were assessed under these stresses to explore whether a crystalline protein had better storage stability than a conventionally produced one. Samples were maintained at different relative humidities (RH) and temperatures for 20 weeks and stabilities estimated in solid and aqueous states. Differential scanning calorimetry (DSC) and thermogravimetry (TGA) characterised solid samples. Fourier transform Raman (FT-Raman) spectroscopy analysed solid material and aqueous solutions. High sensitivity differential scanning calorimetry (HSDSC) and enzymatic assays were used to monitor solutions. DSC and HSDSC data revealed that crystals maintained thermal stability at high RH; spray drying appreciably changed melting characteristics. These results correlated with enzymatic assays that demonstrated good activity retention for crystals but less so for spray-dried material (e.g. 95 and 87% relative to fresh samples after 20 weeks at 40 degrees C/75% RH). FT-Raman analysis showed that crystallised lysozyme better-maintained protein conformational integrity compared to spray-dried samples in accelerated stability studies. Based on TGA data, spray-dried protein absorbed water on storage under humid conditions, which induced instability. Thus, crystallisation enhanced storage stability of lysozyme with negligible loss of activity.
International Journal of Pharmaceutics 08/2004; 278(2):209-19. · 3.35 Impact Factor
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ABSTRACT: An approach to inhibit the crystallisation of amorphous mannitol was investigated. Boric acid was selected as a model additive for a fundamental study of its ability to retard crystallisation and to facilitate characterisation of the properties of the amorphous solid. At concentrations above 5% (w/w) of boric acid, the DSC scans indicated that a totally amorphous solid could be prepared by cooling the melted pre-mixture under ambient conditions. An increase in the glass transition temperature (T(g)) was observed with a corresponding increase in boric acid content, and their relationship was well fitted by the Gordon-Taylor equation. This result suggested that mannitol and boric acid mixed homogeneously. The crystallisation profiles of the resultant amorphous compositions were best described by the Avrami-Eroféev equation (n=1/3), which indicated that random nucleation and three-dimensional crystal growth was the best-fitting mechanism of this crystallisation. The activation energy of crystallisation decreased with increasing boric acid content, indicating that the temperature dependency for crystallisation decreased with increasing boric acid content. Furthermore, the rate of crystallisation at 30 degrees C for mannitol alone was 7000 times higher than that of mannitol containing 7.5% (w/w) of boric acid.
International Journal of Pharmaceutics 07/2003; 258(1-2):109-20. · 3.35 Impact Factor
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ABSTRACT: We have previously shown that by exposing one form of mannitol to high relative humidity, a moisture-induced polymorphic transition of mannitol with a concurrent change in particle morphology occurs [Int. J. Pharm. 247 (2002) 69]. In this paper, we propose that if these changes occur during a wet-granulation procedure, it may be possible to make bring about an in situ size-reduction of mannitol with compaction property enhancement. Powder X-ray diffraction and scanning electron microscopy confirmed that a polymorphic transition (the delta form forming the beta form) had occurred on wet-granulation, and that a concomitant morphology change resulted in an agglomerate consisting of filament-like fine primary crystals (delta-granule). The aim of present study was to evaluate the compression properties of this agglomerate. The compact compressed with delta-granules possessed a tensile strength 1.5 times higher than other mannitol samples. Heckel analysis indicated that the mannitol compression process proceeded by deformation without fragmentation and was thus particle size dependent. The delta-granule showed enhanced plastic deformability, due to its unique particle structure. Because the intrinsic compression properties of the polymorphs were similar, the primary particle size and specific surface area of mannitol were indicated to be the major contributing factors for the improved compaction behaviour, rather than the polymorphic transition. When using the delta-granule as an excipient for a tablet formulation containing a high amount of phenylpropanolamine hydrochloride (PPA) as a poorly compactable model drug, excellent tablets could be prepared without capping, whereas conventional mannitol produced capped tablets.
International Journal of Pharmaceutics 07/2003; 258(1-2):121-31. · 3.35 Impact Factor
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ABSTRACT: Aqueous solutions of hen egg lysozyme (3% w/v) were dispersed and precipitated by a homogenous mixture of supercritical carbon dioxide-ethanol using the Solution Enhanced Dispersion by Supercritical fluid (SEDS) process. The effects of different working conditions, such as temperature, pressure and the flow rates of the solution and ethanol, on the particle-formation process were studied. The morphology, particle size and size distribution and biological activity of the protein were determined. The precipitates were examined with high-sensitivity differential scanning calorimetry (HSDSC) and high-performance cation-exchange chromatography. Particle size measurements showed the precipitates to be aggregates with primary particles of size 1-5 microm. The similarity of HSDSC data for unprocessed and processed samples indicated that the different physical forces that stabilise the native form of lysozyme are unchanged after SEDS processing. From FT-Raman spectroscopic studies secondary structural changes were observed in certain SEDS-produced lysozyme, with most processed samples displaying a slightly more disordered secondary structure than the unprocessed sample. However, SEDS samples produced at 200 bar and 40 degrees C exhibited negligible disturbance. Thus the SEDS process utilising aqueous solution was able to bring about size reduction of lysozyme with minimal loss of biological activity.
Journal of Pharmacy and Pharmacology 03/2003; 55(2):185-92. · 2.17 Impact Factor
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ABSTRACT: The development of proteins as therapeutic agents is challenging partly due to their inherent instabilities. Consequently, crystallisation and spray drying techniques were assessed to determine their effects on protein integrity using lysozyme as a model protein. Unprocessed, crystallised and spray-dried lysozyme were characterised by: thermal analysis using hot stage microscopy (HSM), differential scanning calorimetry (DSC), high sensitivity differential scanning calorimetry (HSDSC) and thermogravimetry (TGA); and spectroscopic analysis employing Fourier transform Raman (FT-Raman). Moisture contents were determined by TGA and Karl Fisher titration (KFT). Enzymatic assay measured biological activity. HSM showed no changes in crystals until complete melting. TGA and KFT indicated that spray-dried lysozyme contained a lower moisture content than crystals, hence the higher apparent thermal stability was shown by DSC. HSDSC revealed that crystallisation and spray drying did not affect the denaturation temperature of lysozyme in solution when compared with unprocessed material. However, in the solid state, FT-Raman spectra showed perturbation of the conformational structure of spray-dried sample, whereas crystal conformation remained intact. Enzymatic assay revealed increased activity retention of crystals compared with spray-dried powder. Hence, crystals maintained the conformational integrity and activity of lysozyme in solution.
International Journal of Pharmaceutics 11/2002; 247(1-2):79-90. · 3.35 Impact Factor
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ABSTRACT: 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.
International Journal of Pharmaceutics 11/2002; 247(1-2):69-77. · 3.35 Impact Factor
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ABSTRACT: Pure anhydrous polymorphs of carbamazepine were prepared by solution-enhanced dispersion with supercritical fluids (SEDS™). Crystallization of the polymorphs was studied. Mechanisms are proposed that consider the thermodynamics of carbamazepine, supersaturation in the SEDS™ process, and the binary phase equilibria of organic solvents and the carbon dioxide antisolvent. α-Carbamazepine was crystallized at high supersaturations and low temperatures, β-carbamazepine crystallized from a methanol–carbon dioxide phase split, and γ-carbamazepine crystallized via nucleation at high temperatures and low supersaturation. © 2001 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:1115–1124, 2001
Journal of Pharmaceutical Sciences 07/2001; 90(8):1115 - 1124. · 3.06 Impact Factor
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ABSTRACT: No The thermodynamic status of -carbamazepine has been clarified using equilibrium solubility measurements, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), heated X-ray powder diffraction (XRPD), and temperature-controlled X-ray scattering techniques. -Carbamazepine is the least stable of the three well-characterized anhydrous polymorphs of carbamazepine at 25°C. In addition, it was confirmed that -carbamazepine undergoes an exothermic transition to -carbamazepine at 130°C. The novel technique of time-resolved simultaneous small- and wide-angle X-ray scattering has been successfully applied to monitor this transition in situ. It was concluded that -carbamazepine has a monotropic relationship with -carbamazepine.
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ABSTRACT: No Pure anhydrous polymorphs of carbamazepine were prepared by solution-enhanced dispersion with supercritical fluids (SEDSTM). Crystallization of the polymorphs was studied. Mechanisms are proposed that consider the thermodynamics of carbamazepine, supersaturation in the SEDSTM process, and the binary phase equilibria of organic solvents and the carbon dioxide antisolvent. -Carbamazepine was crystallized at high supersaturations and low temperatures, -carbamazepine crystallized from a methanol-carbon dioxide phase split, and -carbamazepine crystallized via nucleation at high temperatures and low supersaturation.
