Tamoxifen-Loaded Eudragit Nanoparticles: Quality by Design Approach for Optimization of Nanoparticles as Delivery System

Nanoparticles have numerous applications as drug carriers in drug delivery. The aim of the study was to produce tamoxifen nanoparticles with a defined size and higher encapsulation for efficient tissue uptake with controlled drug release. The quality by design approach was utilized to produce tamoxifen-loaded Eudragit nanoparticles by identifying the significant process variables using the nanoprecipitation method. The process variables (amount of drug, polymer, and surfactant) were altered to analyze the influence on particle size (PS), % encapsulation efficiency (EE). The results showed that the drug and polymer individually as well as collectively have an impact on PS, while the surfactant has no impact on the PS. The %EE was influenced by the surfactant individually and in interaction with the drug. The linear regression model was endorsed to fit the data showing high R2 values (PS, 0.9146, %EE, 0.9070) and low p values (PS, 0.0004, EE, 0.0005). The PS and EE were confirmed to be 178 nm and 90%, respectively. The nanoparticles were of spherical shape, as confirmed by SEM and TEM. The FTIR confirmed the absence of any incompatibility among the ingredients. The TGA confirmed that the NPs were thermally stable. The in vitro release predicted that the drug release followed Higuchi model.

Development and Application of a Modified Method to Determine the Encapsulation Efficiency of Proteins in Polymer Matrices

A modified method to determine protein encapsulation efficiency in polymer matrices has been developed and applied to two proteins and two polymers to demonstrate its wide range of applicability. This study was pursued due to the wide variation in reported protein encapsulation efficiency of polymer-based microcapsules, even when the protein, the polymer, and the microcapsule manufacturing method were consistent. Hemoglobin (Hb) and bovine serum albumin (BSA) were chosen as model proteins and ethylcellulose and poly(lactic-co-glycolic acid) (PLGA) as model polymers. The polymer of the microcapsule was dissolved in dichloromethane/ethanol or dichloromethane/ethyl acetate for ethylcellulose or PLGA microcapsules, respectively. Liberated proteins were simultaneously precipitated, pelleted by centrifugation, isolated by decanting the polymer solution, redissolved in 10% w/v sodium dodecyl sulfate in 0.8 N sodium hydroxide, and quantified using a modified Lowry assay. Blank microcapsules and exogenously added proteins demonstrated ≥ 93.8% recovery of proteins. The mean encapsulation efficiency of ethylcellulose or PLGA microcapsules was 52.4 or 76.9% for Hb and 86.4 or 74.7% for BSA, respectively. This demonstrates the effective use of centrifugation and the importance of an appropriate cosolvent system in the measure of encapsulation efficiency where one solvent dissolves the polymer while the other solvent quantitatively precipitates the liberated protein. It is evident that an alkaline solution of sodium dodecyl sulfate is efficient at quantitatively dissolving precipitated proteins. Remediation of problems observed with current methods and high reproducibility suggest that this modified method is generally applicable to the measure of protein encapsulation efficiency of polymer microcapsules.

Use of extrusion aids for successful production of Kollidon® CL-SF pellets by extrusion-spheronization

OBJECTIVE

Fine particle ethylcellulose (FPEC) or poly(ethylene oxide) (PEO) addition to a Kollidon CL-SF was investigated to address low yield and poor sphericity in extruded-spheronized pellets.

SIGNIFICANCE

The success of crospovidone as a diluent in extrusion-spheronization was dependent on a small particle size of the polymer. FPEC aided production of rugged and spherical pellets using a large particle size grade, Polyplasdone^® XL. PEO acted as an extrusion-spheronization aid when ethylcellulose was the diluent. These extrusion-spheronization aids could serve in this role when Kollidon^® CL-SF (K CL-SF) is the diluent.

METHODS

The influence of formulation and process variables on pellet properties was investigated using design of experiments. A planetary mixer was used to prepare powder blends and the wetted mass after addition of water. An EXD 60 extruder produced extrudate that was spheronized in a Q230 marumerizer. Wet pellets were dried in a forced-air oven.

RESULTS

FPEC improved rounding up but reduced pellet yield. Poly(ethylene oxide) imparted desired characteristics to the wetted mass, the extrudate, and the spheronized pellets. Pellet average diameter, yield, sphericity, aspect ratio, friability, and dissolution profile were assessed. Equations for pellet characteristics facilitated discussion of the influences of factors and their interactions. Optimization was performed on pellets that included PEO.

CONCLUSIONS

PEO proved to be an exceptional extrusion-spheronization aid in the preparation of pellets using K CL-SF. It facilitated wetted mass extrusion with minimal mass loss to the extruder, and markedly improved the sphericity of the pellets produced by marumerization. Immediate release pellets were obtained.

Investigation of the in vitro performance difference of drug-Soluplus® and drug-PEG 6000 dispersions when prepared using spray drying or lyophilization

Purpose: To evaluate the physicochemical and in vitro characteristics of solid dispersions using BCS II model drugs with Soluplus® and one of its component homopolymers, PEG 6000. Methods: Nifedipine (NIF) and sulfamethoxazole (SMX) of 99.3% and 99.5% purity, respectively, were selected as BCS II model drugs, such that an improved dissolution rate and concentration in the gastrointestinal tract should increase oral bioavailability. Soluplus® is an amorphous, tri-block, graft co-polymer with polyvinyl caprolactam, polyvinyl acetate, and polyethylene glycol (PCL:PVAc:PEG6000) in the ratio 57:30:13. PEG 6000 (BASF) is a waxy material with melting point of about 60 °C. Solid dispersions were prepared using lyophilization or spray drying techniques. Dissolution study, crystallinity content, and analysis for new chemical bond formation have been used to evaluate the dispersed materials. Results: Although each polymer improved the drug dissolution rate, dissolution from Soluplus® was slower. Enhanced dissolution rates were observed with NIF solid dispersions, but the dissolution profiles were quite different due to the selected technique, polymer, and dissolution medium. For SMX, there was similarity across the dissolution profiles despite the medium, polymer, or applied technique. Each polymer was able to maintain an elevated drug concentration over the three hour duration of the dissolution profile, i.e., supersaturation was supported by the polymer. DSC thermograms revealed no melting endotherm, suggesting that the drug is amorphous or molecularly dispersed. Conclusion: NIF and SMX solid dispersions were successfully prepared by spray drying and lyophilization using Soluplus® or PEG 6000. Each polymer enhanced the drug dissolution rate; NIF dissolution rate was improved to a greater extent. Dispersions with PEG 6000 had a faster dissolution rate due to its hydrophilic nature. DSC analysis showed that no crystalline material exists in the dispersions.

Use of к-carrageenan, chitosan and Carbopol 974P in extruded and spheronized pellets that are devoid of MCC

The search for excipients to replace microcrystalline cellulose (MCC) in the production of pellets by extrusion-spheronization in cases of drug incompatibility or the lack of pellet matrix disintegration forms the basis of this study. A combination of к-carrageenan as a spheronization aid, chitosan as a diluent and Carbopol(®) 974P as a binder in the production of pellets containing no MCC has been investigated using acetaminophen as a model drug. Design of experiments allowed assessment of formulation and processing effects on pellet responses that included size, shape, fines, yield and friability. Statistical analysis revealed that the main factors and some of the two-factor interactions had a significant effect on pellet characteristics. Formulations containing high levels of к-carrageenan required more water to produce a wetted mass with good extrudability and extrudate capable of being spheronized. Although only a low level of Carbopol was used in the formulation, it imparted cohesiveness to the wetted mass as well as the extrudate. Furthermore, it was discovered that Carbopol could act as an extrusion aid, enabling the wetted mass to flow easily through the extruder screen holes without building up heat. Spherical and rugged pellets were produced that met the immediate release criterion.

A Quality by Experimental Design Approach to Assess the Effect of Formulation and Process Variables on the Extrusion and Spheronization of Drug-Loaded Pellets Containing Polyplasdone® XL-10

Successful pellet production has been reported in literature with cross-linked poly(vinylpyrrolidone), Polyplasdone® XL-10 and INF-10. In the present study, a quality by experimental design approach was used to assess several formulation and process parameter effects on the characteristics of Polyplasdone® XL-10 pellets, including pellet size, shape, yield, usable yield, friability, and number of fines. The hypothesis is that design of experiments and appropriate data analysis allow optimization of the Polyplasdone product. High drug loading was achieved using caffeine, a moderately soluble drug to allow in vitro release studies. A five-factor, two-level, half-fractional factorial design (Resolution V) with center point batches allowed mathematical modeling of the influence of the factors and their two-factor interactions on five of the responses. The five factors were Polyplasdone® level in the powder blend, volume of water in the wet massing step, wet mixing time, spheronizer speed, and spheronization time. Each factor and/or its two-factor interaction with another factor influenced pellet characteristics. The behavior of these materials under various processing conditions and component levels during extrusion-spheronization have been assessed, discussed, and explained based on the results. Numerical optimization with a desirability of 0.974 was possible because curvature and lack of fit were not significant with any of the model equations. The values predicted by the optimization described well the observed responses. The hypothesis was thus supported.

Use of fine particle ethylcellulose as the diluent in the production of pellets by extrusion-spheronization

The effect of small ethylcellulose particle size on the manufacture and properties of pellets produced by extrusion-spheronization was investigated. A factorial design revealed the effects of microcrystalline cellulose (MCC), polyethylene oxide (PEO), water, and spheronization speed and time on pellet properties. Response surface modeling allowed optimization of the responses with expansion to a central composite design. Pellet yield, size, shape, friability and drug release profile were studied, along with surface and interior morphology. Pellets were spherical irrespective of the formulation and process variables and exhibited physical and mechanical characteristics appropriate for further processing. Yield in the 12/20 mesh cut was lower with FPEC than observed with coarse particle ethylcellulose (CPEC), but FPEC-containing pellets were more rugged and the PEO to obtain optimal pellets was lower for FPEC compared to CPEC. Immediate release products were obtained and ethylcellulose particle size was of no consequence to drug release. Observed responses for the optimized product agreed with predicted values, demonstrating the success of the optimization procedure. These results suggest that FPEC is a good diluent for extrusion-spheronization.

Chitosan as a pore former in coated beads for colon specific drug delivery of 5-ASA

A multiparticulate product for colon-specific delivery of a small molecule drug has been developed and characterized. Microcrystalline cellulose core beads containing 5-aminosalicylic acid produced by extrusion-spheronization were coated with chitosan and Aquacoat(®) ECD mixtures according to a factorial design. Coated beads were characterized in terms of drug release, shape, and friability. The optimum formulation was enteric coated and exposed to media simulating conditions in the stomach, small intestine, and colon. Release studies in simulated intestinal fluid revealed that the drug release rate from the coated beads, which were spherical and rugged, depended on the level of chitosan in the coat and the coat thickness. Enlarged pores observed on the surface of the coated beads exposed to the medium containing rat cecal and colonic enzymes are believed to have caused a significant enhancement of the drug release rate compared to the control exposed only to simulated gastric and intestinal fluids. The release mechanisms involved polymer relaxation and dissolved drug diffusion for simulated intestinal fluid and simulated colonic fluid, respectively. From the facilitated drug release in a colonic environment and the inhibition of drug release under gastric and intestinal conditions, it can be concluded that this multiparticulate system demonstrates the potential for colon-specific drug delivery.

Rheological and mucoadhesive characterization of poly(vinylpyrrolidone) hydrogels designed for nasal mucosal drug delivery

Poly(vinylpyrrolidone) (PVP) hydrogels were crosslinked by gamma irradiation to add structure and rigidity, and then rheological and mucoadhesive properties were evaluated. The effects of PVP concentration, radiation dose, and additives, such as poly(ethylene glycol) (PEG) and glycerol, on rheological properties were investigated. In an oscillatory analysis, an increase in polymer concentrations increased the storage modulus (G') and the loss modulus (G″) but decreased the loss tangent (tan δ < 1). The relationships between G'or G″ and the frequency levelled off at higher frequencies, which is indicative of polymer chain entanglement and network formation. Each of the 6% PVP hydrogels exhibited plastic flow with rheopectic behavior. PVP concentration, radiation dose, and the presence of PEG or glycerol influenced the rheological and mucoadhesive properties of the hydrogels. However, adding acyclovir to the formulation did not have a profound effect on the rheological behavior of the hydrogels. The results suggest that a 3% PVP hydrogel with 1% PEG crosslinked with 20 kGy is the most appropriate hydrogel. The results demonstrated the successful complementary application of oscillatory and flow rheometry to characterize and develop a hydrogel for mucosal drug administration.

Influence of cyclodextrin complexation with NSAIDs on NSAID/cold stress-induced gastric ulceration in rats

The aim of this work was to study the ability of beta-cyclodextrin (beta-CD) or hydroxypropyl beta-cyclodextrin (HP-beta-CD) to ameliorate the induction of gastric ulcers by a nonsteroidal anti-inflammatory drug, indomethacin or piroxicam, in rats exposed to restraint and hypothermic stress at 4 degrees C. Using oral gavage, rats fasted for 72 h were administered the equivalent of a 100 mg/kg dose of the assigned drug, alone or with the designated cyclodextrin (CD). The rats were placed in suitable rodent restrainers and then placed inside a ventilated refrigerator maintained at a temperature of 4 degrees C. Six hours later, each animal was removed, anaesthetized with ether, and the abdomen opened. Each stomach was removed, opened along the greater curvature and gently rinsed with isotonic saline solution. The induced gastric ulcers were examined and assessed with the help of a 10x binocular magnifier. Pronounced and marked gastric ulceration with complete loss of the mucosa, extensive deposition of fibrin and dense neutrophilic infiltrate were observed in rats treated with each of the drugs alone. Treatment with indomethacin or piroxicam alone induced ulcer indices of 26 +/- 2.3 or 14 +/- 1.8, respectively. However, beta-CD and HP-beta-CD each significantly suppressed ulceration due to restraint and cold stress. Rats treated with indomethacin or piroxicam in the presence of either beta-CD or HP-beta-CD exhibited normal tissues. Therefore, beta-CD and HP-beta-CD act as protective agents against gastrointestinal disorders produced by restraint and cold stress, even with the added stress from administration of either indomethacin or piroxicam.

Extruded and spheronized beads containing Carbopol® 974P to deliver nonelectrolytes and salts of weakly basic drugs

The purpose of the study was to explore the utilization of Carbopol 974P, NF, resin in a bead dosage form manufactured by extrusion and spheronization. It was possible to prepare beads in this study by using calcium chloride to overcome the tack problem associated with wetted Carbopol 974P. The actives included both salts of weakly basic drugs (chlorpheniramine maleate and diphenhydramine hydrochloride) and nonelectrolytes (caffeine and dyphylline) which have a broad range of solubilities. Nonelectrolytes were released faster than the salts of weakly basic drugs. This is contrary to the behavior typically seen with a matrix system where the more soluble drug is released faster than a poorly soluble one. In the results of the present study, the solubility does not determine the drug release rate. Ionic interactions between the protonated amines of the salts and the carboxylates of the Carbopol resin are suggested to be the reason for the slower release of the salts of weakly basic drugs. Data from tack measurements confirm that this ionic interaction affects the behavior of the wetted Carbopol. In addition to the drug release profiles, bead average diameter, roundness, friability, and density were also determined.

PEO and MPEG in high drug load extruded and spheronized beads that are devoid of MCC

A means to produce extruded-spheronized beads, devoid of microcrystalline cellulose (MCC) and with a high drug load (greater than 80%, w/w), is presented. Immediate release bead product with a high yield (greater than 60% of 1mm diameter beads) and low friability (mass loss less than 4.0%) that were spherical to the naked eye (roundness score less than 1.20) were obtained. The formulation consists only of water-soluble components, taking advantage of the properties of soluble polyethylene oxide (PEO) and methoxypolyethylene glycol (MPEG). This approach incorporates minimal processing aids, with wetted PEO providing the apparent plasticity and cohesiveness, and MPEG550 providing the apparent self-lubricating characteristics necessary for successful extrusion and subsequent spheronization into beads. The success of this approach has important implications in cases where high drug load beads are desired, but where MCC cannot be used due to chemical incompatibility or where complete release cannot be achieved with MCC-containing beads.

Modulatinn Intestinal Uptake of Atenolol Usinn Niosomes as Drun Permeation Enhancers

It is well established through the last decade that niosomes have potential applications as drug carriers either to improve drug permeation across membranes or targeting to specific tissues. Having a considerable ability to improve the permeability of drugs through lipoid membranes, niosomes have been utilized as carriers to enhance atenolol absorption from the gastrointestinal tract. Two methods have been adopted to prepare niosomes, the proniosome-derived method (A) and the conventional film hydration method (B). The products from the two methods were compared in terms of their morphology, vesicle size, drug encapsulation efficiency, in vitro drug release and enhancement effect on drug permeation across the intestinal membrane using an everted sac technique. Proniosome-derived niosomes were smoother and exhibited a smaller (5 μm) vesicle size compared to those prepared by conventional methods (12 μm). High encapsulation efficiencies of 98.6% and 93.4% were achieved by methods A and B, respectively. In vitro drug release has been significantly retarded from both types of niosomes. Comparing to pure drug, which dissolved completely in 15 min, only 8.9% and 9.9% of the entrapped drug was released in the same time period. The drug release kinetics showed non-Fickian (anomalous) behavior. Permeation through an everted intestinal sac showed a significant enhancement effect (more than 4 fold) for both types of niosomes compared to untrapped drug; however, the difference between the two types of niosomes was not significant

Water Distribution Studies Within Microcrystalline Cellulose and Chitosan using Differential Scanning Calorimetry and Dynamic Vapor Sorption Analysis

The objective of the study was to assess and compare the interaction and distribution of water within microcrystalline cellulose (MCC) and chitosan by differential scanning calorimetry (DSC) and dynamic vapor sorption analysis. The amounts of nonfreezing and freezing water in hydrated samples were determined from melting endotherms obtained by DSC. After accounting for the percent crystallinity of MCC and chitosan, no statistically significant difference was observed in their ability to bind water molecules per repeating unit at the minimum water content at which freezing water is evident. Exposure of chitosan to water for 30 min was sufficient to achieve equilibration at 61% w/w actual water content. The moisture sorption profiles were analyzed according to the GAB and Young and Nelson equations. The adsorbed monolayer, externally adsorbed moisture, and internally absorbed moisture were not statistically different for MCC and chitosan after accounting for the amorphous content of the polymers. These studies suggest that chitosan can act as a "molecular sponge," and thus aid in the production of beads by extrusion and spheronization.

Effects of preparative parameters on the properties of chitosan hydrogel beads containing Candida rugosa lipase

The influences of the pH, tripolyphosphate (TPP) concentration, and ionic strength of the gelling medium on the entrapment efficiency, release, and activity of lipase in chitosan hydrogel beads were studied. A solution of Candida rugosa lipase was prepared in a 1.5% w/v chitosan and 1% (v/v) acetic acid medium, and dropped into a TPP solution. Release of lipase in pH 7.2 Tris buffer was monitored over 36 h using the micro BCA protein assay. The activity of the entrapped enzyme was assayed using the Sigma lipase activity method. Following preliminary studies, an experimental design was followed to develop mathematical models that describe bead characteristics as functions of the pH and the TPP concentration in the gelling medium. The pH and the TPP concentration each had an effect on the entrapment, retention, and activity of lipase. Entrapped lipase retained a high degree of activity in multiple reactions. The ionic strength, in the range studied, exerted a minimal effect on bead characteristics. Statistical analysis allowed optimization within the factor space with respect to maximizing the enzyme entrapment efficiency and activity, and also minimizing the amount released after 36 h in the Tris buffer.

Extruded and Spheronized Beads Containing No Microcrystalline Cellulose: Influence of Formulation and Process Variables

The purposes of this study were to investigate the use of chitosan in the manufacture of beads by extrusion-spheronization without inclusion of microcrystalline cellulose, and to study the effect of formulation and process variables on the characteristics of the beads. Beads containing chitosan, fine particle ethylcellulose, hydroxypropyl methylcellulose (HPMC), and caffeine as the model drug were manufactured. Bead size, yield, shape, friability, density, porosity, and release studies were determined. Spherical beads with good mechanical properties could be manufactured without microcrystalline cellulose. Release studies showed that there was immediate release of drug from the beads. A five factor, half fraction screening design was employed to study the effect of formulation variables and process variables on the properties of the beads. Statistical analysis indicated that formulation variables such as the chitosan content, HPMC content, and water content, and process variables such as the spheronizer speed and extruder speed significantly affected the physical properties of the beads. The bead size decreased with an increase in chitosan content. Significant two-factor interactions exist between the variables for several of the measured responses. Beads with high percentage yield and high sphericity can be obtained at high chitosan content, and low HPMC content, water content, spheronizer speed, and extruder speed. Less friable beads can be obtained at high levels of studied formulation variables and low levels of studied process variables. Beads of high density and low porosity can be manufactured at high levels of the studied formulation and process variables. Regression equations were generated using Statgraphics Plus software that can be used to develop formulations with desired bead properties. Chitosan was useful to provide beads of acceptable physical properties using water as a granulating fluid in the extrusion-spheronization process.

Studies on the interaction of water with ethylcellulose: effect of polymer particle size

The purpose of this research was to investigate the interaction of water with ethylcellulose samples and assess the effect of particle size on the interaction. The distribution of water within coarse particle ethylcellulose (CPEC; average particle size 310 micro m) and fine particle ethylcellulose (FPEC; average particle size 9.7 micro m) of 7 cps viscosity grade was assessed by differential scanning calorimetry (DSC) and dynamic vapor sorption analysis. The amounts of nonfreezing and freezing water in hydrated samples were determined from melting endotherms obtained by DSC. An increase in water content resulted in an increase in the enthalpy of fusion of water for the two particle size fractions of EC. The amount of nonfreezable water was not affected by the change in particle size at low water contents. Exposure of ethylcellulose to water for 30 minutes is sufficient to achieve equilibration within the hydrated polymer at 47% wt/wt water content. The moisture sorption profiles were analyzed according to the Guggenheim-Anderson-de Boer (GAB) and Young and Nelson equations, which can help to distinguish moisture distribution in different physical forms. The amount of externally adsorbed moisture was greater in the case of FPEC. Internally absorbed moisture was evident only with the CPEC. In light of these results, an explanation is offered for the success of FPEC in wet-granulation methods where CPEC was not successful.

Wet granulation fine particle ethylcellulose tablets: effect of production variables and mathematical modeling of drug release

In the present study, the applicability of fine particle ethylcellulose (FPEC) to produce matrix tablets by a wet granulation technique was evaluated. The effect of various formulation and process variables, such as FPEC content, hardness of the tablet, and solubility of the drug, on the release of drug from these tablets was examined. Tablets were prepared by wet granulation of drug and FPEC in an appropriate mass ratio. Theophylline, caffeine, and dyphylline were selected as nonionizable model drugs with solubilities from 8.3 to 330 mg/mL at 25 degrees C. Ibuprofen, phenylpropanolamine hydrochloride, and pseudoephedrine hydrochloride were selected as ionizable drugs with solubilities from 0.1 to 2000 mg/mL at 25 degrees C. Drug release studies were conducted in 37 degrees C water with UV detection. As the FPEC content and the hardness of the tablets increased, the release rate of the drug decreased. The drug release rate increased with an increase in the solubility of the drug. Model equations, intended to elucidate the drug release mechanism, were fitted to the release data. Parameters were generated and data presented by SAS software. The Akaike Information Criterion was also considered to ascertain the best-fit equation. Fickian diffusion and polymer relaxation were the release mechanisms for nonionizable and ionizable drugs.

Immobilization of lipase using hydrophilic polymers in the form of hydrogel beads

The purpose of this study was to immobilize lipase (triacylglycerol ester hydrolase, E.C. 3.1.1.3) from Candida rugosa using various polymers in the form of beads, to evaluate enzyme loading, leaching, and activity; and to characterize the beads. Agarose, alginate, and chitosan were the polymers selected to immobilize lipase by entrapment. Agarose beads exhibited undesirable swelling in the leaching and activity medium and the polymer was not used further. Alginate or chitosan beads were prepared by ionic gelation using calcium chloride or sodium tripolyphosphate, respectively, as the cross-linking agent in the gelling solution. Some hatches of beads of each polymer were freeze dried. The results show that alginate beads leached substantially more enzyme than did chitosan beads. Entrapment efficiency, however, was the same for different chitosan levels as well as different alginate levels (43-50%). Activity in alginate was low at 240 +/- 33 and 220 +/- 26, compared to 1,110 +/- 51 and 1,150 +/- 11 units/ml in chitosan, for fresh and freeze-dried beads, respectively. The higher lipase activity in chitosan beads compared to that in alginate beads could be attributed to an alginate-enzyme interaction. It can be concluded that chitosan is a polymer worthy of pursuit to immobilize lipase.

Molecular weight and degree of deacetylation effects on lipase-loaded chitosan bead characteristics

The effects of the molecular weight (MW) and degree of deacetylation (DD) of chitosan on chitosan hydrogel beads were characterized, and the entrapment efficiency, release of entrapped lipase, and activity of immobilized Candida rugosa lipase were investigated. Fresh and freeze-dried beads were characterized. A solution of lipase was prepared in a 1.5% (w/v) chitosan and 1% (v/v) acetic acid medium, and then dropped into a tripolyphosphate solution to prepare the beads. The release studies were performed over 36 h. The enzyme activity was assayed using the Sigma lipase activity method. Chitosan with high MW and DD resulted in a higher loading. A lower activity was observed for beads produced with high DD chitosan. MW did not have a marked effect on the activity. The release study revealed that enzyme release increased to a maximum when the bead was manufactured with a low MW and a moderate to high DD chitosan sample. Freeze drying did not affect the release or the activity of the lipase. Chitosan with a high MW and DD can thus improve loading and reduce the release of lipase in these beads. The choice of chitosan can affect the activity normalized for lipase loading, and beads with desirable qualities can be produced.

In vitro degradation of chitosan by bacterial enzymes from rat cecal and colonic contents

The degradative activities of extracellular and cell-associated portions of rat cecal and colonic enzymes, whose activities are comparable to that in the human colon, against five chitosan samples were characterized. The effects of the molecular weight (MW) and degree of deacetylation (DD) of chitosan on its susceptibility to degradation were investigated. In addition, the degradation function of rat bacterial enzymes was compared to that of a commercially available almond emulsin beta-glucosidase that contains a chitinase. The results show that rat bacterial enzymes had the ability to degrade chitosan with extracellular enzymes exhibiting a more profound effect than did cell-associated enzymes. The reaction to bacterial enzymes degradation was dependent on both the MW and DD of the chitosan sample. Those samples with a lower MW and lower DD were more susceptible substrates. A similar degradation function of rat bacterial enzymes and of almond emulsin beta-glucosidase on chitosan was revealed, which indicates that almond emulsin beta-glucosidase might be able to be used as an in vitro enzyme system to predict the large intestinal degradation of chitosan.

An in vitro evaluation of a chitosan-containing multiparticulate system for macromolecule delivery to the colon

A multiparticulate system of chitosan hydrogel beads has been investigated for colon-specific delivery of macromolecules using fluorescein isothiocyanate-labeled bovine serum albumin as a model protein. The hydrogel bead was formed by polyelectrolyte complexation of chitosan with its counterion, tripolyphosphate (TPP). The protein release experiments were carried out in vitro under different conditions to simulate the pH and times likely to be encountered during intestinal transit to the colon. The results show that the hydrogel beads were degraded by rat cecal and colonic enzymes, resulting in a marked acceleration in the release of protein. The ability of rat cecal and colonic enzymes to degrade chitosan hydrogel beads was independent of pretreatment conditions. A commercial beta-glucosidase preparation containing a chitinase did not have a similar effect on the chitosan bead, even though it has been found to mimic the degradation function of rat cecal and colonic enzymes in vitro for chitosan in solution. Degradation of the chitosan-TPP hydrogel beads in the presence of rat cecal and colonic enzymes indicates the potential of this multiparticulate system to serve as a carrier to deliver macromolecules specifically to the colon.

Fine-Particle ethylcellulose as a tablet binder in direct compression, immediate-release tablets

Ethylcellullose has traditionally been used in tablets as a binder in an alcohol solution form. In the present study, fine-particle ethylcellulose (FPEC) was used as a binder to manufacture immediate-release tablets by the direct compression technique. The binding potential of FPEC is compared to that of commercially available coarse-particle ethylcellulose at the same viscosity grade and to that of hydrophilic binders. The compression force setting was kept constant for all batches. The concentration of the binder was varied from 5% to 25%. Acetaminophen was used as a model drug because capping is a problem frequently observed during high-speed compaction and further processing of acetaminophen tablets. In this study, there would be an increase in the contact area with FPEC and hence greater bond formation. This greater bond formation should be able to reduce the problem of capping in tablets containing highly elastic materials such as acetaminophen. Tablets were evaluated based on the following tests: weight variation, extent of capping, hardness, friability, disintegration, and dissolution. Based on the results of these tests, FPEC proved to be an effective binder for directly compressed acetaminophen tablets. The 10% and 15% formulations of FPEC passed all the tests and also produced the hardest tablets.

In vitro degradation of chitosan by a commercial enzyme preparation: effect of molecular weight and degree of deacetylation

A commercially available almond emulsin beta-glucosidase preparation has been reported to have chitobiose activity, and can hydrolyze chitin substrates due to a chitinase present in the enzyme preparation. This beta-glucosidase preparation was used to investigate hydrolytic activity on five chitosan samples with different molecular weight and degree of deacetylation. The degree of deacetylation and molecular weight of the chitosan samples were determined using a circular dichroism and a viscometric method, respectively. The hydrolytic activity of this beta-glucosidase preparation on chitosan was monitored viscometrically as the most convenient means of screening. Solutions of chitosan in pH 5.0 acetate buffer were prepared using the different viscosity grades of chitosan. The specific viscosity, measured after addition of beta-glucosidase to the above solutions, decreased dramatically over time in comparison to that of the respective control mixture without enzyme. Eadie-Hofstee plots established that hydrolysis of chitosan by this enzyme preparation obeyed Michaelis-Menten kinetics. Apparent Michaelis-Menten parameters and initial degradation rates were calculated and compared to determine the influences of the degree of deacetylation and molecular weight on the hydrolysis. The results show that higher molecular weight and higher degree of deacetylation chitosans possessed a lower affinity for the enzyme and a slower degradation rate. Faster degradation rates, then, are expected with lower molecular weight and low degree of deacetylation chitosans. Hydrolysis of these chitosan samples confirms the existence of a chitinase in the almond emulsin beta-glucosidase preparation, and further studies are warranted.

Evaluation of quantitative structure property relationships necessary for enantioresolution with lambda- and sulfobutylether lambda-carrageenan in capillary electrophoresis

Lambda-carrageenan, a linear, high molecular weight sulfated polysaccharide, was successfully employed in both its native and sulfobutyl derivatized form as a chiral selector in capillary electrophoresis for the separation of enantiomers of basic pharmaceutical compounds. In order to characterize the chiral selectivity properties of this chiral selector, various structurally related racemic compounds were analyzed for enantiomeric interactions using capillary electrophoresis. The results of these studies were then rationalized and analyzed utilizing a general quantitative structure-property relationship (QSPR) evaluation in order to predict critical analyte structural requirements for successful enantiomeric separation. Important structural components of the analytes were found to include the aromatic content, the type of substitution on the aromatic ring, presence of a primary or secondary protonated amine, and an overall positive charge to the molecule.

Optimization of lambda-carrageenan as a chiral selector in capillary electrophoresis separations

Lambda-carrageenan, a linear high molecular weight sulfated polysaccharide, was employed as a chiral selector in capillary electrophoresis for the separation of enantiomers of weakly basic pharmaceutical compounds. In order to improve the utility of the chiral selector, the purity and concentration of the lambda-carrageenan and other important capillary electrophoresis method parameters were investigated. The results indicated that the purity and concentration of the lambda-carrageenan, ionic strength of the buffer, and temperature were critical to successful enantioseparation. These new method conditions were then applied to previously investigated beta-blockers (such as propranolol HCl and pindolol) and racemic tryptophan derivatives. These studies were successful in identifying important method conditions for the improved enantioselectivity with lambda-carrageenan.

Formulation and process considerations for beads containing Carbopol 974P, NF resin made by extrusion-spheronization

Preliminary studies revealed that Carbopol 974P, NF resin could be incorporated into beads manufactured by extrusion and spheronization, and can slow the release of a highly water soluble drug if calcium chloride was included in the granulating fluid to reduce the tack of the wetted polymer. In this study, the same approach was used to produce high quality chlorpheniramine maleate beads with a prolonged release duration. Because of the complex nature of the extrusion and spheronization process and the various components in the bead formulations, a statistically sound factorial experiment was considered for this study. A one-half fraction of a two level factorial design with three center points was employed to estimate the effects of simultaneously modifying multiple process and formulation variables, including the Carbopol concentration, calcium chloride concentration, water content, and the spheronization speed and time. Product yield, average bead roundness, and the drug release profile were selected as responses. Increasing the Carbopol content across the experimental range resulted in a significant (P<0.05) reduction in the percentage drug released at 25, 40, and 60 min. Results suggest that combining the conditions of high Carbopol, high water, and low calcium chloride levels with low spheronization speeds at long spheronization times produce the highest quality bead with the longest drug release duration.

The antimicrobial activity of vancomycin in the presence and absence of sodium carboxymethyl starch

The purpose of this work was to determine any effects the presence of sodium carboxymethyl starch may have on the antimicrobial activity of vancomycin given a previously described interaction between vancomycin and sodium carboxymethyl starch. In particular, the in-vitro activity of vancomycin against two clinically relevant bacteria, Staphylococcus aureus and Enterococcus faecalis, was studied in the presence of varying concentrations of sodium carboxymethyl starch. From two independent studies conducted using an agar dilution method, it appeared that the binding of vancomycin to sodium carboxymethyl starch had no effect on the in-vitro antimicrobial activity of vancomycin. The minimum inhibitory concentration of vancomycin against S. aureus in the presence of as much as 1 mg mL(-1) sodium carboxymethyl starch was similar to that of the control where no sodium carboxymethyl starch was added (1-4 microg mL(-1) vs 1-2 microg mL(-1), respectively). Likewise, the minimum inhibitory concentration of vancomycin against E. faecalis in the presence of 1 mg mL(-1) sodium carboxymethyl starch was also similar to that of the control where no sodium carboxymethyl starch was added (1-4 microg mL(-1) vs 1-4 microg mL(-1), respectively). However, there may be factors in the in-vitro method, such as high ionic strength, that could disrupt the interaction between vancomycin and sodium carboxymethyl starch. Therefore, the possibility of diminished vancomycin activity in-vivo cannot be ruled out. A small percentage (8-10%) of vancomycin was determined to be bound to sodium carboxymethyl starch in broth media. Given these results, the impact of sodium carboxymethyl starch on the in-vitro antimicrobial activity of vancomycin is expected to be minimal. Binding studies could not be conducted with gelled agar due to its semi-solid state.

The effect of the aqueous solubility of xanthine derivatives on the release mechanism from ethylcellulose matrix tablets

Release data from ethylcellulose (EC) matrix tablets was analyzed to determine which release equation provides the best fit to the data and to observe the effect of drug solubility on the release mechanism(s). Tablets were prepared by direct compression of drug, EC, and lubricant in an appropriate mass ratio to achieve a high and a low drug loading. Theophylline, caffeine, and dyphylline were selected as non-electrolyte xanthine derivatives with solubilities from 8.3 to 330 mg/ml at 25 degrees C. Drug release studies were conducted in 37 degrees C water with UV detection at 272 nm. Several equations to characterize release mechanisms were tested with respect to the release data. Drug diffusion, polymer relaxation, and tablet erosion were the mechanisms considered. Parameters were generated and ANOVA data presented by WinNonlin Pro(R) software. The Akaike Information Criterion was also considered to ascertain the best fit equation. At high drug loading, drug was released by a diffusion mechanism with a rate constant that increased with an increase in aqueous solubility. At low drug loading, polymer relaxation also became a component of the release mechanism. However, its contribution to drug release was less pronounced as solubility decreases, becoming negligible in the case of theophylline.

Differential molar heat capacities to test ideal solubility estimations

PURPOSE

Calculation of the ideal solubility of a crystalline solute in a liquid solvent requires knowledge of the difference in the molar heat capacity at constant pressure of the solid and the supercooled liquid forms of the solute, delta Cp. Since this parameter is not usually known, two assumptions have been used to simplify the expression. The first is that delta Cp can be considered equal to zero; the alternate assumption is that the molar entropy of fusion, delta Sf, is an estimate of delta Cp. Reports claiming the superiority of one assumption over the other, on the basis of calculations done using experimentally determined parameters, have appeared in the literature. The validity of the assumptions in predicting the ideal solubility of five structurally unrelated compounds of pharmaceutical interest, with melting points in the range 420 to 470 K, was evaluated in this study.

METHODS

Solid and liquid heat capacities of each compound near its melting point were determined using differential scanning calorimetry. Linear equations describing the heat capacities were extrapolated to the melting point to generate the differential molar heat capacity.

RESULTS

Linear data were obtained for both crystal and liquid heat capacities of sample and test compounds. For each sample, ideal solubility at 298 K was calculated and compared to the two estimates generated using literature equations based on the differential molar heat capacity assumptions.

CONCLUSIONS

For the compounds studied, delta Cp was not negligible and was closer to delta Sf than to zero. However, neither of the two assumptions was valid for accurately estimating the ideal solubility as given by the full equation.

Drug solubility effects on predicting optimum conditions for extrusion and spheronization of pellets

This paper explores the utility of aqueous solubility of structurally similar drugs in predicting optimum conditions for extrusion and spheronization of pellets using response surface methodology. Pharmacologically active xanthine derivatives exhibiting widely varying aqueous solubility were used to determine optimum conditions for pelletization. The amount of water added to the formulation, wet mixing time, and spheronizing time were explored in a series of central composite experimental designs to exhaustively explore and mathematically model the response surfaces for each drug. Using a marketed microcrystalline cellulose excipient, optimum extrusion and spheronization conditions for less soluble drugs required more water, a longer wet mixing time, and prolonged spheronizing times. Results were similar when a new microcrystalline cellulose was substituted, except that more water was required. When comparing results for different drugs, a strong linear relationship was observed between the aqueous solubility of the drug and the water content required for optimum pellet production. The water content range over which quality pellets could be produced was much broader for poorly soluble drugs. Aqueous solubility of the active component appears to be a good predictor for the water requirements for optimum extrusion and spheronization of pellets for pharmaceutical applications.

Lambda-carrageenan: a novel chiral selector for capillary electrophoresis

Lambda-carrageenan, a linear high molecular weight sulfated polysaccharide, has been employed as a chiral selector in capillary electrophoresis for the separation of enantiomers of weakly basic pharmaceutical compounds. The racemic compounds that were enantioresolved included propranolol, pindolol, tryptophanol, laudanosine and laudanosoline. In addition, the diastereomeric pair of cinchonine and cinchonidine were also resolved. Method conditions such as buffer pH, electrolyte concentration, column temperature, and chiral selector concentration were found to be important for improvement of enantioselectivity.

A comparison of two quality assessment methods for emulsions

A common method of assessing the quality of emulsions is to evaluate the size distribution of the globules of the internal phase. The primary aim of this work is to compare the sensitivity of this test to an alternative method. The sizes of the globules of two emulsions, an oral emulsion and a total parenteral nutrition (TPN) emulsion, were determined using a light microscope. Globule size analyses were performed upon preparation and during storage of the emulsions. Using a computer program specially developed for this study, the recorded diameters were placed into size groups and the volumes of each of the measured globules was determined. For each size group, the total volume of all the globules within the group and the volume percentage of the oil phase represented by the group were calculated. The volume distribution of the internal phase across the size groups was found to predict emulsion instability better than the globule number distribution and thus is a better determinant of emulsion quality. This technique may have general application in the evaluation of TPN emulsions and other spheres, such as liposomes.