Håkan Wikström

Immobilisation and evaluation of a vancomycin chiral stationary phase for capillary electrochromatography.

The macrocyclic antibiotic, vancomycin, is covalently bonded to LiChrospher diol silica packed columns and evaluated in capillary electrochromatography (CEC) both in the reversed-phase and polar organic mode. Initially, capillaries were packed with 5 microm LiChrospher 100 A diol silica and evaluated in CEC with a reversed-phase biphenyl-pyrene achiral test resulting in resolution and efficiency values of ca. 2.5 and 100000 plates meter(-1), respectively. Repeatability for this test (resolution and efficiency) was also examined and found to be acceptable for both run-to-run (n=5, 0.74% and 1.5%) and column-to-column (n=5, 3.4% and 9.0%), respectively. Similar results were obtained when the 10 microm LiChrospher 1000 A diol silica was examined with the exception of efficiency, where a reduced plate height value of four times lower was obtained compared to the 100 A material. A simple three step in-situ vancomycin immobilisation procedure was subsequently carried out on these packed diol columns. Selectivity was obtained for thalidomide enantiomers on this vancomycin chiral stationary phase in reversed-phase CEC with resolution and efficiency values of ca. 2.5 and 80000 plates meter(-1), with acceptable repeatability (n=8) 0.9% and 3.0%, respectively. Selectivity was also obtained for thalidomide enantiomers on this phase in the polar organic mode with resolution and efficiency values of ca. 2.5 and 120000 plates meter(-1), with acceptable repeatability (n=7) 0.9% and 2.0%, respectively. It was possible to deduce from a chemometric design carried out for evaluating the mobile phase component effects that organic modifier ratio, MeOH/MeCN, played a significant role in controlling both resolution and efficiency. It was also possible to separate a number of basic analytes including four beta-adrenergic blocking agents in the polar organic mode albeit with lower resolution and efficiency values, ca. 1.5 and 45000 plates meter(-1), respectively.

Improved Understanding of Factors Contributing to Quantification of Anhydrate/Hydrate Powder Mixtures

Different spectroscopic approaches have proved to be excellent analytical tools for monitoring process-induced transformations of active pharmaceutical ingredients during pharmaceutical unit operations. In order to use these tools effectively, it is necessary to build calibration models that describe the relationship between the amount of each solid-state form of interest and the spectroscopic signal. In this study, near-infrared (NIR) and Raman spectroscopic methods have been evaluated for the quantification of hydrate and anhydrate forms in pharmaceutical powders. Process type spectrometers were used to collect the data and the role of the sampling procedure was examined. Multivariate regression models were compared with traditional univariate calibrations and special emphasis was placed on data treatment prior to multivariate modeling by partial least squares (PLS). It was found that the measured sample volume greatly affected the performance of the model whereby the calibrations were significantly improved by utilizing a larger sampling area. In addition, multivariate regression did not always improve the predictability of the data compared to univariate analysis. The data treatment prior to multivariate modeling had a significant influence on the quality of predictions with standard normal variate transformation generally proving to be the best preprocessing method. When the appropriate sampling techniques and data analysis methods were utilized, both NIR and Raman spectroscopy were found to be suitable methods for the quantification of anhydrate/hydrate in powder systems, and thus the method of choice will depend on the conditions in the process under investigation.

Understanding the Tendency of Amorphous Solid Dispersions to Undergo Amorphous–Amorphous Phase Separation in the Presence of Absorbed Moisture

Formulation of an amorphous solid dispersion (ASD) is one of the methods commonly considered to increase the bioavailability of a poorly water-soluble small-molecule active pharmaceutical ingredient (API). However, many factors have to be considered in designing an API–polymer system, including any potential changes to the physical stability of the API. In this study, the tendency of ASD systems containing a poorly water-soluble API and a polymer to undergo amorphous–amorphous phase separation was evaluated following exposure to moisture at increasing relative humidity. Infrared spectroscopy was used as the primary method to investigate the phase behavior of the systems. In general, it was observed that stronger drug–polymer interactions, low-ASD hygroscopicity, and a less hydrophobic API led to the formation of systems resistant to moisture-induced amorphous–amorphous phase separation. Orthogonal partial least squares analysis provided further insight into the systems, confirming the importance of the aforementioned properties. In order to design a more physically stable ASD that is resistant to moisture-induced amorphous–amorphous phase separation, it is important to consider the interplay between these properties.

Enantioselective reversed-phase and non-aqueous capillary electrochromatography using a teicoplanin chiral stationary phase

Enantiomeric separation of chiral pharmaceuticals is carried out in aqueous and non-aqueous packed capillary electrochromatography (CEC) using a teicoplanin chiral stationary phase (CSP). Capillaries were slurry packed with 5 microm 100-A porous silica particles modified with teicoplanin and initially evaluated using a non-aqueous polar organic mode system suitability test for the separation of metoprolol enantiomers (Rs = 2.3 and 53000 plates m(-1)). A number of pharmaceutical drugs were subsequently screened with enantioselectivity obtained for 25 racemic solutes including examples of neutral, acidic and basic molecules such as coumachlor (Rs = 3.0 and 86000 plates m(-1)) and alprenolol (Rs = 3.3 and 135000 plates m(-1)) in reversed-phase and polar organic mode, respectively. A statistical experimental design was used to investigate the effects of non-aqueous polar organic mobile phase parameters on the CEC electroosmotic flow, resolution and peak efficiency for two model solutes. Results primarily indicated that higher efficiency and resolution values could be attained at higher methanol contents which is similar to findings obtained on this phase in liquid chromatography.

Comparison of sampling techniques for in-line monitoring using Raman spectroscopy.

Raman spectroscopy is currently of interest as a process monitoring tool for pharmaceutical unit operations. In this study, the performance characteristics of Raman spectrometers with different sampling optics have been investigated in the context of process monitoring, with emphasis being placed on assessing homogeneity in powder blends and following changes in solid-state form during wet granulation. A novel large spot non-contact Raman sampling device was compared with a traditional small spot size non-contact sampling device and an immersion probe. The large spot non-contact optics provided significant advantages over the standard systems both as a result of the enhanced sampling volume and because of the greater robustness of the system to fluctuations in the sampling distance during the wet granulation process.

A quality by design approach to investigate the effect of mannitol and dicalcium phosphate qualities on roll compaction

Roll compaction is a continuous process for solid dosage form manufacturing increasingly popular within pharmaceutical industry. Although roll compaction has become an established technique for dry granulation, the influence of material properties is still not fully understood. In this study, a quality by design (QbD) approach was utilized, not only to understand the influence of different qualities of mannitol and dicalcium phosphate (DCP), but also to predict critical quality attributes of the drug product based solely on the material properties of that filler. By describing each filler quality in terms of several representative physical properties, orthogonal projections to latent structures (OPLS) was used to understand and predict how those properties affected drug product intermediates as well as critical quality attributes of the final drug product. These models were then validated by predicting product attributes for filler qualities not used in the model construction. The results of this study confirmed that the tensile strength reduction, known to affect plastic materials when roll compacted, is not prominent when using brittle materials. Some qualities of these fillers actually demonstrated improved compactability following roll compaction. While direct compression qualities are frequently used for roll compacted drug products because of their excellent flowability and good compaction properties, this study revealed that granules from these qualities were more poor flowing than the corresponding powder blends, which was not seen for granules from traditional qualities. The QbD approach used in this study could be extended beyond fillers. Thus any new compound/ingredient would first be characterized and then suitable formulation characteristics could be determined in silico, without running any additional experiments.

Manipulating Theophylline Monohydrate Formation During High-Shear Wet Granulation Through Improved Understanding of the Role of Pharmaceutical Excipients

PurposeTo investigate the effect of common pharmaceutical excipients on the kinetics of theophylline monohydrate formation during high-shear wet granulation.Materials and methodsA mixture of anhydrous theophylline and the excipient was granulated in a high-shear granulator, using water as the granulation liquid. Non-contact Raman spectroscopy was used to monitor the rate of transformation of anhydrate to hydrate during the granulation process. The kinetics of conversion was also monitored in slurries of theophylline whereby the excipients were added to the aqueous phase. Optical microscopy was used to visualize the transformation and to measure the linear growth rates of hydrate crystals in the presence and absence of the excipients.ResultsAt pharmaceutically relevant amounts of excipient, the transformation kinetics of theophylline was unchanged for the majority of excipients tested. However, when granulating with low concentrations of some commonly used polymeric binders, the transformation kinetics could be significantly retarded. For example, methylcellulose polymers delayed both the onset of hydrate formation as well as retarding the transformation rate. When 0.3% (w/w) of hydroxypropyl methylcellulose was added to a model formulation containing 30% (w/w) theophylline anhydrous, the formation of the monohydrate could be completely prevented over the time period of the granulation experiment, without significantly affecting the granular properties. Microscopic observations of hydrate formation in the presence of the polymer revealed that the polymers that inhibited hydrate formation reduced the hydrate crystal growth rates and influenced hydrate morphology.ConclusionsRaman spectroscopy is a useful technique to monitor hydrate formation during wet granulation. Some commonly used polymeric pharmaceutical excipients can be used to manipulate theophylline hydrate formation in aqueous pharmaceutical environments. These excipients may affect either the nucleation and/or the growth of the hydrate phase.

Analysis of the Effect of Particle Size on Polymorphic Quantitation by Raman Spectroscopy

Raman spectroscopy has been widely used to monitor various aspects of the crystallization process. Although it has long been known that particle size can influence Raman signal, relatively little research has been conducted in this area, in particular for mixtures of organic materials. The aim of this study was to investigate the effect of particle size on quantification of polymorphic mixtures. Several sets of calibration samples containing different particle size fractions were prepared and Raman spectra were collected with different probes. Calibration models were built using both univariate and multivariate analysis. It was found that, for a single component system, Raman intensity decreased with increasing particle size. For mixtures, calibration models generated from the same particle size distribution as the sample yielded relatively good predictions of the actual sample composition. However, if the particle sizes of the calibration and unknown samples were different, prediction errors resulted. For extreme differences in particle sizes, prediction errors of up to 20% were observed. Prediction errors could be minimized by changing the sampling optics employed.

An investigation into the influence of counterion on the properties of some amorphous organic salts.

Amorphous solids and crystalline salts are both of interest as a means of improving the dissolution characteristics and apparent solubility of poorly water soluble active pharmaceutical ingredients which have low bioavailability in humans. The theory and selection of both crystalline drug substance salt forms and amorphous products have been extensively studied. However, less is known about the impact of different counterions on the properties of amorphous drug substance salts. In this study, several salts of either nicardipine or propranolol were prepared and characterized with respect to glass transition temperature, crystallization tendency and moisture sorption behavior. Although the moisture sorption behavior and crystallization tendency varied depending on the counterion used, no trends were readily apparent. The glass transition temperature was found to be dependent on the counterion used to form the salt, and was higher in all instances for the salts than for the neutral compound. Several molecular descriptors were calculated for the various counterions, and multivariate analysis was used to build a model that successfully correlated Tg with a number of these parameters. Important parameters which influenced Tg included counterion pKa and electrophilicity index. In conclusion, it is apparent that, as for crystalline salts, the counterion has an effect on the properties of amorphous materials.

Combining experimental design and orthogonal projections to latent structures to study the influence of microcrystalline cellulose properties on roll compaction

Roll compaction is gaining importance in pharmaceutical industry for the dry granulation of heat or moisture sensitive powder blends with poor flowing properties prior to tabletting. We studied the influence of microcrystalline cellulose (MCC) properties on the roll compaction process and the consecutive steps in tablet manufacturing. Four dissimilar MCC grades, selected by subjecting their physical characteristics to principal components analysis, and three speed ratios, i.e. the ratio of the feed screw speed and the roll speed of the roll compactor, were included in a full factorial design. Orthogonal projection to latent structures was then used to model the properties of the resulting roll compacted products (ribbons, granules and tablets) as a function of the physical MCC properties and the speed ratio. This modified version of partial least squares regression separates variation in the design correlated to the considered response from the variation orthogonal to that response. The contributions of the MCC properties and the speed ratio to the predictive and orthogonal components of the models were used to evaluate the effect of the design variation. The models indicated that several MCC properties, e.g. bulk density and compressibility, affected all granule and tablet properties, but only one studied ribbon property: porosity. After roll compaction, Ceolus KG 1000 resulted in tablets with obvious higher tensile strength and lower disintegration time compared to the other MCC grades. This study confirmed that the particle size increase caused by roll compaction is highly responsible for the tensile strength decrease of the tablets.