The secondary nucleation threshold and crystal growth of alpha-glucose monohydrate in aqueous solution

Investigation of the secondary nucleation threshold (SNT) of alpha-glucose monohydrate was conducted in aqueous solutions in agitated batch systems for the temperature range 10 to 40 degrees C. The width of the SNT decreased as the induction time increased and was found to be temperature independent when supersaturation was based on the absolute concentration driving force. Nonnucleating seeded batch bulk crystallizations of this sugar were performed isothermally in the same temperature range as the SNT experiments, and within the SNT region to avoid nucleation. The growth kinetics were found to be linearly dependent on the supersaturation of total glucose in the system when the mutarotation reaction is not rate limiting. The growth rate constant increases with increasing temperature and follows an Arrhenius relationship with an activation energy of 50 +/- 2 kJ/mol. alpha-Glucose monohydrate shows significant crystal growth rate dispersion (GRD). For the seeds used, the 95% range of growth rates was within a factor of 6 for seeds with a narrow particle size distribution, and 8 for seeds with a wider distribution that was used at 25 degrees C. The results will be used to model the significance of the mutarotation reaction on the overall crystallization rate of D-glucose in industrial crystallization.

The effect of selected water-soluble excipients on the dissolution of paracetamol and ibuprofen

The purpose of this investigation was to study the dissolution behavior of paracetamol and ibuprofen in the presence of a range of selected potential excipients. First, a pH-solubility profile was generated for both drugs, and the effect of changing hydrodynamic conditions on the intrinsic dissolution rate was investigated. It was established that both drugs dissolved according to the diffusion-layer model. Paracetamol solubility (approximately 20.3 mg mL -1) did not vary from pH 1.2-8.0, corresponding to the in vivo range in the gastrointestinal tract. Ibuprofen had an intrinsic solubility of approximately 0.06 mg mL-1, and pKa was calculated as 4.4. Second, the effects of selected potential excipients (lactose, potassium bicarbonate, sodium bicarbonate, sodium chloride, and tartaric acid) were evaluated by measuring the effect of the inclusion of each additive in the dissolution medium on drug solubility, drug intrinsic dissolution rate, and solution viscosity. The results were evaluated using the diffusion-layer model, and it was determined that for paracetamol, the collected data fitted the model for all the excipients studied. For ibuprofen, it was found that there were differences between the excipients that raised the solution pH above the pK a to those that did not. For the excipients raising the pH above the pKa, the effect on intrinsic dissolution rate was not as high as that expected from the change in drug solubility. It was postulated that this might be due to lack of penetration of the excipient into the drug boundary layer microenvironment. Formulators may calculate the effect of adding an excipient based on solubility increases but may not find the dissolution rate improvement expected. Copyright © 2005 Taylor & Francis Inc.

Modified release of beclometasone dipropionate from chitosan-basedd spray-dried respirable powders

Dry powders for inhalation were prepared by spray drying a 30% v/v aqueous ethanol formulation containing beclometasone dipropionate (BDP), lactose, leucine and chitosan (low, medium or high molecular weight (MW), or combinations thereof). Following physical characterisation of the powders, the aerosolisation and dissolution properties of the powders were investigated using Multi-Stage Liquid Impinger and USP II dissolution apparatus, respectively. The powders were highly dispersible, with emitted doses in excess of 90% of loaded powder aerosolised from a Spinhaler dry powder inhaler. The fine particle fraction (FPF) was observed to decrease, whereas the time for 100% drug release increased, with increasing chitosan MW. For example, the low MW formulation exhibited an FPF of 64% and a 100% dissolution time of 2 h, whereas the high MW formulation demonstrated an FPF of 54% and a dissolution time of 12 h. These powders would be anticipated to deposit predominately in the lower regions of the lung following inhalation, and then undergo delayed rather than instantaneous drug release, offering the potential to reduce dosing frequency and improve patient compliance. (c) 2008 Elsevier B.V. All rights reserved.

The influence of formulation components on the aerosolisation properties of spray-dried powders

Dry powders suitable for inhalation containing β-estradiol, leucine as a dispersibility enhancer and lactose as a bulking agent were prepared by spray-drying from aqueous ethanol formulations. The influence of formulation components on the characteristics of the resultant spray-dried powders was examined through the use of a range of ethanol concentrations (10-50% v/v) in the solvent used to prepare the initial formulations. Additionally, the amount of leucine required to act as a dispersibility enhancer was investigated by varying the amount of leucine added to the formulation prior to spray-drying. Following spray-drying, resultant powders were characterised using scanning electron microscopy, laser diffraction and tapped density measurements, and the aerosolisation performance determined using Twin Stage Impinger and Andersen Cascade Impactor analysis. We demonstrate that selection of appropriate solvent systems and leucine concentration allows the preparation of spray-dried powders that display enhanced aerosolisation properties, and would be predicted to exhibit high deposition in the lower regions of the respiratory tract. © 2005 Elsevier B.V. All rights reserved.

The use of amino acids to enhance the aerosolisation of spray-dried powders for pulmonary gene therapy

Background Pulmonary delivery of gene therapy offers the potential for the treatment of a range of lung conditions, including cystic fibrosis, asthma and lung cancer. Spray-drying may be used to prepare dry powders for inhalation; however, aerosolisation of such powders is limited, resulting in poor lung deposition and biological functionality. In this study, we examine the use of amino acids (arginine, aspartic acid, threonine, phenylalanine) to enhance the aerosolisation of spray-dried powders containing model non-viral gene vectors. Methods Lipid/polycation/pDNA (LPD) vectors, in the presence or absence of amino acids, were dispersed in lactose solutions, and spray-dried to produce appropriately sized dry powders. Scanning electron microscopy and laser diffraction were used to determine particle morphology and diameter, respectively. Gel electrophoresis was used to examine the influence of amino acids on the structural integrity of the LPD complex. In vitro cell (A.549) transfection was used to determine the biological functionality of the dry powders, and the in vitro aerosolisation performance was assessed using a multistage liquid impinger (MSLI). Results Both gel electrophoresis and in vitro cell transfection indicated that certain amino acids (aspartic acid, threonine) can adversely affect the integrity and biological functionality of the LPD complex. All amino acids significantly increased the aerosolisation of the powder, with the arginine and phenylalanine powders showing optimal deposition in the lower stages of the MSLI. Conclusions Amino acids can be used to enhance the aerosolisation of spray-dried powders for respiratory gene delivery, allowing the development of stable and viable formulations for pulmonary gene therapy.

Enzymatic production of oligosaccharides in centrifugal fields

The aims of this work have been to identify an enzymatic reaction system suitable to investigate and develop the high-speed centrifuge as a novel reaction system for performing such reactions. The production of galacto-oligosaccharides by the trans-galactosyl activity of the enzyme β-galactosidase on lactose monohydrate was identified as a model enzymatic system to elucidate the principles of this type of process. Galacto-oligosaccharides have attracted considerable commercial interest as food additives which have been shown to be beneficial to the health of the human gastrointestinal tract. The development of a single unit operation capable of controlling the biosynthesis of galacto-oligosaccharides whilst simultaneously separating the enzyme from the reaction products would reduce downstream processing costs. This thesis shows for the first time that by using a combination of (a) immobilised or insolubilised β-galactosidase , (b) a rate-zonal centrifugation technique, and (c) various applied centrifugal fields, that a high-speed centrifuge could be used to control the formation of galacto-oligosaccharides whilst removing the enzyme from the reaction products. By layering a suspension of insolubilised β-galactosidase on top of a lactose monohydrate density gradient and centrifuging, the applied centrifugal fields generated produced sedimentation of the enzyme particles through the substrate. The higher sedimentation rate of the enzyme compared to those of the reaction products allowed for separation to take place. Complete sedimentation, or pelleting of the enzyme permits the possible recovery and re-use. Insolubilisation of the enzyme allowed it to be sedimented through the substrate gradient using much lower applied centrifugal fields than that required to sediment free soluble enzyme and this allowed for less expensive centrifugation equipment to be used. Using free soluble and insolubilised β-galactosidase stirred-batch reactions were performed to investigate the kinetics of lactose monohydrate hydrolysis and galacto-oligosaccharide formation. Based on these results a preliminary mathematical model based on Michaelis-Menten kinetics was produced. It was found that the enzyme insolubilisation process using a chemical cross-linking agent did not affect the process of galacto-oligosaccharide formation. Centrifugation experiments were performed and it was found that by varying the applied centrifugal fields that the yield of galacto-oligosaccharides could be controlled. The higher the applied centrifugal fields the lower the yield of galacto-oligosaccharides. By increasing the applied centrifugal fields the 'contact time' between the sedimenting enzyme and the substrate was reduced, which produced lower yields. A novel technique involving pulsing the insolubilised enzyme through the substrate gradient was developed and this was found to produce higher yields of galacto-oligosaccharide compared to using a single enzyme loading equivalent to the total combined activity of the pulses. Comparison of the galacto-oligosaccharide yields between stirred-batch and centrifugation reactions showed that the applied centrifugal fields did not adversely affect the transgalactosyl activity of the insolubilised enzyme.

Combined bioreaction and separation in a simulated counter-current chromatographic bioreactor-separator system

The objective of this work has been to investigate the principle of combined bioreaction and separation in a simulated counter-current chromatographic bioreactor-separator system (SCCR-S). The SCCR-S system consisted of twelve 5.4cm i.d x 75cm long columns packed with calcium charged cross-linked polystyrene resin. Three bioreactions, namely the saccharification of modified starch to maltose and dextrin using the enzyme maltogenase, the hydrolysis of lactose to galactose and glucose in the presence of the enzyme lactase and the biosynthesis of dextran from sucrose using the enzyme dextransucrase. Combined bioreaction and separation has been successfully carried out in the SCCR-S system for the saccharification of modified starch to maltose and dextrin. The effects of the operating parameters (switch time, eluent flowrate, feed concentration and enzyme activity) on the performance of the SCCR-S system were investigated. By using an eluent of dilute enzyme solution, starch conversions of up to 60% were achieved using lower amounts of enzyme than the theoretical amount required by a conventional bioreactor to produce the same amount of maltose over the same time period. Comparing the SCCR-S system to a continuous annular chromatograph (CRAC) for the saccharification of modified starch showed that the SCCR-S system required only 34.6-47.3% of the amount of enzyme required by the CRAC. The SCCR-S system was operated in the batch and continuous modes as a bioreactor-separator for the hydrolysis of lactose to galactose and glucose. By operating the system in the continuous mode, the operating parameters were further investigated. During these experiments the eluent was deionised water and the enzyme was introduced into the system through the same port as the feed. The galactose produced was retarded and moved with the stationary phase to be purge as the galactose rich product (GalRP) while the glucose moved with the mobile phase and was collected as the glucose rich product (GRP). By operating at up to 30%w/v lactose feed concentrations, complete conversions were achieved using only 48% of the theoretical amount of enzyme required by a conventional bioreactor to hydrolyse the same amount of glucose over the same time period. The main operating parameters affecting the performance of the SCCR-S system operating in the batch mode were investigated and the results compared to those of the continuous operation of the SCCR-S system. . During the biosynthesis of dextran in the SCCR-S system, a method of on-line regeneration of the resin was required to operate the system continuously. Complete conversion was achieved at sucrose feed concentrations of 5%w/v with fructose rich. products (FRP) of up to 100% obtained. The dextran rich products were contaninated by small amounts of glucose and levan formed during the bioreaction. Mathematical modelling and computer simulation of the SCCR-S. system operating in the continuous mode for the hydrolysis of lactose has been carried out. .

Bioreaction and separation in batch chromatographic columns

The objective of this work has been to study the behaviour and performance of a batch chromatographic column under simultaneous bioreaction and separation conditions for several carbohydrate feedstocks. Four bioreactions were chosen, namely the hydrolysis of sucrose to glucose and fructose using the enzyme invertase, the hydrolysis of inulin to fructose and glucose using inulinase, the hydrolysis of lactose to glucose and galactose using lactase and the isomerization of glucose to fructose using glucose isomerase. The chromatographic columns employed were jacketed glass columns ranging from 1 m to 2 m long and the internal diameter ranging from 0.97 cm to 1.97 cm. The stationary phase used was a cation exchange resin (PUROLITE PCR-833) in the Ca2+ form for the hydrolysis and the Mg2+ form for the isomerization reactions. The mobile phase used was a diluted enzyme solution which was continuously pumped through the chromatographic bed. The substrate was injected at the top of the bed as a pulse. The effect of the parameters pulse size, the amount of substrate solution introduced into the system corresponding to a percentage of the total empty column volume (% TECV), pulse concentration, eluent flowrate and the enzyme activity of the eluent were investigated. For the system sucrose-invertase complete conversions of substrate were achieved for pulse sizes and pulse concentrations of up to 20% TECV and 60% w/v, respectively. Products with purity above 90% were obtained. The enzyme consumption was 45% of the amount theoretically required to produce the same amount of product as in a conventional batch reactor. A value of 27 kg sucrose/m3 resin/h for the throughput of the system was achieved. The systematic investigation of the factors affecting the performance of the batch chromatographic bioreactor-separator was carried out by employing a factorial experimental procedure. The main factors affecting the performance of the system were the flowrate and enzyme activity. For the system inulin-inulinase total conversions were also obtained for pulses sizes of up to 20 % TECV and a pulse concentration of 10 % w/v. Fructose rich fractions with 100 % purity and representing up to 99.4 % of the total fructose generated were obtained with an enzyme consumption of 32 % of the amount theoretically required to produce the same amount of product in a conventional batch reactor. The hydrolysis of lactose by lactase was studied in the glass columns and also in an SCCR-S unit adapted for batch operation, in co-operation with Dr. Shieh, a fellow researcher in the Chemical Engineering and Applied Chemistry Department at Aston University. By operating at up to 30 % w/v lactose feed concentrations complete conversions were obtained and the purities of the products generated were above 90%. An enzyme consumption of 48 % of the amount theoretically required to produce the same amount of product in a conventional batch reactor was achieved. On working with the system glucose-glucose isomerase, which is a reversible reaction, the separation obtained with the stationary phase conditioned in the magnesium form was very poor although the conversion obtained was compatible with those for conventional batch reactors. By working with a mixed pulse of enzyme and substrate, up to 82.5 % of the fructose generated with a purity of 100 % was obtained. The mathematical modelling and computer simulation of the batch chromatographic bioreaction-separation has been performed on a personal computer. A finite difference method was used to solve the partial differential equations and the simulation results showed good agreement with the experimental results.

Ordered mixing of drugs with particulate excipients

A novel direct compression tableting excipient has been made by recrystallisation of lactose. The particles produced had high porosity, high specific surface area and high surface roughness. The resistance to segregation of ordered mixes formed between a model drug; potassium chloride and the excipients recrystallised lactose, spray crystallised maltose-dextrose (Emdexl and a direct compacting sugar (Dipac) was studied using a vibrational segregation model. The highly porous excipients, Emdex and recrystallised lactose formed ordered mixes which did not segregate even at high accelerations and low frequencies whereas the relatively smooth excipient, Dipac, displayed marked segregation in most vibration conditions. The vibrations were related to practical conditions measured in pharmaceutical process machinery. The time required to form an ordered mix was inversely related to the stability of the mix when subjected to vibration. An ultracentrifuge technique was developed to determine the interparticle adhesion forces holding drug and excipient particles together as ordered units. Excipient powders such as Emdex and recrystallised lactose, which formed non-segregating ordered mixes, had high interparticle adhesion forces. Other ordered mixes that segregated when subjected to different vibration conditions were found to have large quantities of weekly-bound drug particles; such mixes included those with Dipac as the carrier excipient as well as those containing a high concentration of drug. The electrostatic properties of different drug and excipient powders were studied using a Faraday well and an electrometer. Excipient powders such as Emdex and recrystallised lactose which formed stable ordered mixes also had a widely different surface charge in comparison with drug particles, whereas Dipac had a similar surface charge to the drug particles and formed unstable ordered mixes. A specially constructed triboelectric charging apparatus based on an air cyclone was developed to increase the affinity of drug particles for different excipient particles. Using triboelectrification to increase the interparticle adhesion forces, the segregation tendencies of unstable ordered mixes were greatly reduced. The stability of ordered mixes is shown to be related to both the surface physical characteristics and the surface electrical properties of the constituent carrier (excipientl particles.

Chitosan-modified dry powder formulations for pulmonary gene delivery

Spray-drying is an effective process for preparing micron-dimensioned particles for pulmonary delivery. Previously, we have demonstrated enhanced dispersibility and fine particle fraction of spray-dried nonviral gene delivery formulations using amino acids or absorption enhancers as dispersibility-enhancing excipients. In this study, we investigate the use of the cationic polymer chitosan as a readily available and biocompatible dispersibility enhancer. Lactose-lipid:polycation:pDNA (LPD) powders were prepared by spray-drying and post-mixed with chitosan or spray-dried chitosan. In addition, the water-soluble chitosan derivative, trimethyl chitosan, was added to the lactose-LPD formulation before spray-drying. Spray-dried chitosan particles, displaying an irregular surface morphology and diameter of less than 2 mu m, readily adsorbed to lactose-LPD particles following mixing. In contrast with the smooth spherical surface of lactose-LPD particles, spray-dried trimethyl chitosan-lactose-LPD particles demonstrated increased surface roughness and a unimodal particle size distribution (mean diameter 3.4 mu m), compared with the multimodal distribution for unmodified lactose-LPD powders (mean diameter 23.7 mu m). The emitted dose and in vitro deposition of chitosan-modified powders was significantly greater than that of unmodified powders. Moreover, the inclusion of chitosan mediated an enhanced level of reporter gene expression. In summary, chitosan enhances the dispersibility and in vitro pulmonary deposition performance of spray-dried powders.

Enhanced dispersibility and deposition of spray-dried powders for pulmonary gene therapy

Spray-drying represents a viable alternative to freeze-drying for preparing dry powder dispersions for delivering macromolecules to the lung. The dispersibility of spray-dried powders is limited however, and needs to be enhanced to improve lung deposition and subsequent biological activity. In this study, we investigate the utility of leucine as a dry powder dispersibility enhancer when added prior to spray-drying a model non-viral gene therapy formulation (lipid:polycation:pDNA, LPD). Freeze-dried lactose-LPD, spray-dried lactose-LPD and spray-dried leucine-lactose-LPD powders were prepared. Scanning electron microscopy showed that leucine, increased the surface roughness of spray-dried lactose particles. Particle size analysis revealed that leucine-containing spray-dried powders were unimodally dispersed with a mean particle diameter of 3.12 μm. Both gel electrophoresis and in vitro cell (A549) transfection showed that leucine may compromise the integrity and biological functionality of the gene therapy vector. The deposition of the leucine containing powder was however significantly enhanced as evidenced by an increase in gene expression mediated by dry powder collected at lower stages of a multistage liquid impinger (MSLI). Further studies are required to determine the potential of leucine as a ubiquitous dispersibility enhancer for a variety of pulmonary formulations. © 2003 Taylor & Francis Ltd.

Measuring the flow properties of small powder samples using an avalanche tester

The feasibility of using a small-scale avalanche tester to measure the flow properties of pharmaceutical lactose powders was examined. The modes of behaviour observed in larger systems were displayed and showed a clear distinction between angular, free-flowing particles and more spherical particles of similar flow characteristics. Angular Lactohale LH100 particles showed slumping behaviour at a rotational frequency of 0.33Hz which disappeared at higher frequencies. Spherical lactose powder with a similar flow function to LH100 only showed rolling behaviour under the same conditions, as did more cohesive powders LH200 and LH300. Further investigation of the LH100 data using Fast Fourier analysis showed that the slumping frequency was 1/10th of the rotational frequency.

Trissoralen um medicamento de baixa dosagem: estudos termoanalíticos da compatibilidade do fármaco-excipientes e determinação de parâmetros de qualidade para cápsulas magistrais

The trioxsalen (Tri) is a low-dose drug used in the treatment of psoriasis and other skin diseases. The aim of the study was applying the thermal analysis and complementary techniques for characterization, evaluation of the trioxsalen stability and components of manipulated pharmaceutical formulations. The thermal behavior of the Tri by TG/DTG-DTA in dynamic atmosphere of synthetic air and nitrogen showed the same profile with a melting peak followed by a volatilization-related event. From the curves TG / DTG is observed a single stage of mass loss. By heating the drug in the stove at temperatures of 80, 240 and 260 °C, it had no change in chemical structure through the techniques of XRD, HPLC, MIR, OM and SEM. From the non-isothermal and isothermal TG kinetic studies was possible to calculate the activation energy and reaction order for the Tri. The drug showed good thermal stability. Studies on drug-excipient compatibility showed interaction of trissoralen with sodium lauryl sulfate 1:1. There was no interaction with aerosol, pregelatinized starch, sodium starch glycolate, cellulose, croscarmellose sodium, magnesium stearate, lactose and mannitol.The characterization of three trioxsalen formulations at concentrations of 2.5, 5, 7.5, 10, 12.5 and 15 mg was performed by DSC, TG / DTG, XRD, NIR and MIR. The PCA classification method based on spectral data from the NIR and MIR of trissoralen formulations allows successful differentiation into three groups. The formulation 3 was the one that best showed analytical profile with the following composition of aerosil excipients, pre-gelatinized starch and cellulose. The activation energy of the volatilization process of the drug was determined in binary mixtures and formulation 3 through fitting and isoconversional methods. The binary mixture with sodium starch glycolate and lactose showed differences in kinetic parameters compared to the drug isolated. The thermoanalytical techniques (DSC and TG / DTG) were shown to be promising methodologies for quantifying trioxsalen obtained by the linearity, selectivity, no use solvents, without sample preparation, speed and practicality.

Determinação da energia de ativação e pureza de medicamentos de referência, genérico e similar utilizando técnicas termoanalíticas

In this work, the reference drugs, generic and similar to the active ingredients acetylsalicylic acid, paracetamol, captopril, hydrochlorothiazide and mebendazole were purchased from local pharmacies and studied by thermogravimetry (TG) and Differential Scanning Calorimetry (DSC). Thermal decomposition was assessed to obtain from the Ozawa method the activation energy in inert atmosphere (nitrogen), using three different heating ratios (5, 10 and 20 o C min-1). The pharmaceutical formulation of the AAS reference was the one who presented different from the others (generic and similar) Thermogravimetric profile indicating likely interaction between the active ingredient and excipients. Was observed at the heating rate of the inverse temperature that no linearity of the data, ie, there was no correlation between the percentage of mass loss and the activation energy involved in the thermal decomposition of the pharmaceutical formulation of the AAS reference log graph. The analysis by differential scanning calorimetry was performed in nitrogen atmosphere with a heating rate of 10 ° C min-1. In the analysis of these same drugs, the data curves found on the melting point were, except for hydrochlorothiazide, are consistent with the literature. Hydrochlorothiazide presented a melting point well below that found in the literature, which may be justified due to the interaction of the active ingredient with the excipient lactose. In the study of purity, using the Van't Hoff equation, the reference drugs hydrochlorothiazide and mebendazole reference generic and showed similar impurity content below the limit established that this equation must be greater than 2.5 mol%

Desempenho de cabras leiteiras alimentadas com diferentes espécies de cactáceas

The objective of this research was to evaluate the production of dairy goats fed different species of cactus. Pluriparous five Saanen goats were used, with nine weeks of lactation, and average live weight of 50 kg ± 4 kg. The animals were distributed in latin square design (5x5) with 5 diets and 5 periods. No differences (P>0,05) were observed in the DM of the experimental diets by getting average values of 2.251,84 g dia-1 , 4,46 %PV e 118,91g kg0,75 . The DM contents of the diets were 50,55 to 55,92% by presenting a maximum variation of 10% between them. A significant difference (P<0,05) water consumption way tendered, between diets with different cactus species. The treatments cactus “Orelha de Elefante Mexicana” and Facheiro had lower water consumption compared to cactus “Palma Miúda. For milk yield no significant difference (P> 0,05) between diets formulated with cactus species, with an average of 1,90 kg/day treatments. The analysis of variance show a significant difference (P<0,05) among treatments for milk corrected to 4% fat and fat production. There was an effect (P<0,05) of the diets with different cactus on the crude protein (CP) and lactose in milk. All treatments with different cactus species can be used for dairy goats in view consumption have afforded sufficient to meet the nutritional requirements for milk nutrients, besides presenting the higher than levels of physical and chemical composition to minimum levels established by current legislation