Magnesium Aluminum Silicate Research Articles

Physical and chemical changes of medicinals in mixtures with adsorbents in the solid state. III. Determination of vapor pressure of solid drugs by steam distillation.

The vapor pressures of solid drugs were determined by the steam distillation method. Experiments using a series of benzoic acid derivatives indicated that this method offered consistent and satisfactory values for vapor pressure at about 100 degrees C. The vapor pressures of two nonsteroidal antiinflammatory drugs, flufenamic acid (FFA) and mefenamic acid (MFA), were found to be 3.8 x 10(-3) and 1.8 x 10(-4) mmHg, respectively. These values explain the difference in the rate of change to the amorphous state between mixtures of each with magnesium aluminum silicate (MAS) when they were stored under reduced pressure. It was concluded that the vapor pressures of solid drugs at about 100 degrees C, as determined by steam distillation, may be suitable indices for predicting whether or not these drugs have an inherent propensity to become amorphous readily in mixtures with an adsorbent.

Physical and chemical changes of medicinals in mixtures with adsorbents in the solid state. IV. Study on reduced-pressure mixing for practical use of amorphous mixtures of flufenamic acid.

Flufenamic acid (FFA) was mixed with magnesium aluminum silicate (MAS) at a reduced pressure of about 10 to 50 mmHg employing a commercial mixer for pharmaceutical production. An amorphous state of FFA in the mixture was efficiently achieved with this equipment, and the dissolution of FFA was enhanced in comparison with that of the physical mixture. Effects of the conditions of mixing, such as pressure, temperature and rotating speed, on dissolution of FFA were determined. Through stability tests at 40 degrees C under both dry and humid conditions, no change in dissolution profiles was recognized in a 5% FFA mixture stored under any conditions. On the other hand, decreases in dissolution behavior were observed in 10% and 20% FFA mixtures when they were stored under humid conditions. These results suggested that humidity should be avoided during the storage of amorphous mixtures of FFA with MAS for production purposes.

Physical and chemical changes of medicinals in mixtures with adsorbents in the solid state. II. Application of reduced pressure treatment for the improvement of dissolution of flufenamic acid.

Flufenamic acid (FFA) was mixed with magnesium aluminum silicate (MAS) and stored at 60 degrees C at a reduced pressure of about 2.5 mmHg. After storage, when its concentration was not more than 20%, FFA was observed by X-ray diffraction and polarizing microscopy to be amorphous. The dissolution of FFA was thus enhanced in comparison with that of a freshly prepared mixture. Furthermore, the dissolution curves showed a typical supersaturation pattern, and the supersaturation state continued longer, the higher the pH value of the dissolution medium. Flufenamic acid, in a mixture with MAS, became amorphous more rapidly at reduced pressure than at atmospheric pressure, and therefore the effect of improved dissolution appeared earlier at reduced pressure. Infrared spectral studies suggested that FFA, after storage at a reduced pressure with MAS, was dispersed monomolecularly in an ionic form. The technique of treating crystalline medicinals, that have poor solubility in water, with adsorbent at reduced pressure may be useful for improving their dissolution characteristics.

Studies on the adsorption and solubility of nalidixic acid

The adsorption of nalidixic acid on certain pharmaceutical additives was investigated and its extent estimated. Also, the effects of various surface-active agents and hydrophilic polymers on the solubility of the drug was determined. The adsorption isotherms have revealed that the degree of adsorption increased in the order; microcrystalline cellulose < ethyl cellulose < silicon dioxide < aluminium magnesium silicate. Studies on the solubility of nalidixic acid at 37°C using different concentrations of hydrophilic polymers have demonstrated that methyl cellulose, polvinylpyrrolidone and polyethylene glycol 6000 have comparable effects. Polyvinyl alcohol caused only a marginal increase in solubility. The surface-active agents, sodium lauryl sulphate and polysorbate 80, also increased solubility of the drug. The values of the heat of solution and the free energy changes were calculated from the Van't Hoff plots. The values of heat of solution for all systems were comparable, but the free energy changes indicate that sodium lauryl sulphate causes the most marked effect on solubility.

Enhancing Mechanical Properties of Polymer Composites by Modification of Surface Acidity or Basicity of Fillers

AbstractThe surface of a powdered glass has been treated to optimize its performance as a filler in polymer composites cast from solution. The aim has been to enhance acid-base interactions between the functional sites of polymers and the surface sites of the glass particles so as to insure complete coverage of the glass particles by adsorbed polymer molecules, and to thereby enhance both the adhesion and dispersion of the filler. The glass chosen for this study is a magnesium aluminum silicate of very low alkali metal content, and its surface sites have negligible basicity and only moderate acidity, as evidenced by weak adsorption of polymethylmethacrylate and negligible adsorption of chlorinated polyvinylchloride from solution in methylene chloride. Because of the negligible surface basicity of the filler, acidic polymers such as polyvinylbutyral and polyvinyl chloride are not adsorbed sufficiently to promote adhesion or dispersibility, and brittle or weak composites result.Surface treatments to enhance surface acidity or basicity of the glass particles were evaluated by electrophoresis in organic solvents, in which acidic particles had negative zeta-potentials and basic particles had positive zeta-potentials; untreated glass particles had zero zetapotentials. The most effective treatments were done with silane coupling agents; amino-silanes provided strong negative zeta-potentials and methacryloxy-silanes provided strong positive zeta-potentials. Angleresolved ESCA spectra showed that the adsorbed amino-silanes averaged about a monolayer in thickness and that half of the nitrogens bonded to the surface as ammonium groups and half were in the outer surface as basic amine groups; the carbonyl oxygens of the methacryloxy-silanes appeared to be bonded to the surface.Heavily-loaded polymer composites were made with the silane-treated and with untreated glass powders, using two acidic binders and a basic binder. The acidic binders were a polyvinylbutyral (PVB) binder cast from solution in a methanol-MIBK mixture, and a post-chlorinated polyvinylchloride (CPVC) binder cast from solution in a mixture of cyclohexane and tetrahydrofuran (THF): the glass transition temperature (Tg) for CPVC is about 140 C, but for PVB it is only about 35 C. The basic polymer (PEHM, polyethyl-hexylmethacrylate) has a Tg well below room temperature. Thus the extension to break in tensile tests was about 1% for CPVC, 10% for PVB, and 20 % for PEHM. About ten stress-strain Instron tests were made on each composite, and the composites with appreciable acid-base interactions between the matrix polymer and the surface sites of the treated glass fillers were in all cases much tougher than those without such acid-base interactions. The brittleness of the polyvinylbutyral composites filled with untreated glass powders was not observed at all on silane-treated glass powders.

Formulation and stability of diazepam suspension compounded from tablets

The stability of diazepam in an extemporaneous suspension compounded from tablets was studied. A diazepam 1 mg/mL suspension was prepared by levigating diazepam 10-mg tablets with ethanol and propylene glycol and incorporating them into a suspension vehicle containing magnesium aluminum silicate and carboxymethylcellulose sodium with flavoring and sweetening agents. Samples of the suspension were stored in amber glass bottles at 5, 22, and 40 degrees C. At various times during the 60-day study period, samples were inspected visually for signs of caking or color change and evaluated for ease of pouring and redispersion. Also at those times, the concentration of diazepam in each sample was determined by a stability-indicating, high-performance liquid chromatography procedure. The concentration of diazepam in each sample was at least 90% of the initial concentration throughout the 60-day storage period. All samples remained homogeneous and showed no signs of caking or settling. A diazepam suspension compounded from tablets was found to be pharmaceutically acceptable and easily pourable and redispersible. The suspension is stable for at least 60 days at room or refrigerated temperature.

Optimization of Slow-Release Tablet Formulations Containing Montmorillonite II. Factors Affecting Drug Release

AbstractThe influence of electrolytes, surfactants in the dissolution medium, and particle size of drug and montmorillonite on the in vitro release of the soluble model drug sodium sulfathiazole from directly compressed slow-release tablets containing 20% drug and 30% magnesium aluminum silicate was investigated. The presence of electrolytes in the dissolution media decreased the release from the tablets. A decrease in release was also observed in deionized water when sodium chloride was included in the tablet formulation. The surface tension of the media appeared to have little influence on the dissolution rate of the drug. Varying the particle size of the drug had a greater effect on release rates than varying the particle size of the montmorillonite clay.

Influence of Viscosity on Absorption from Nitrofurantoin Suspensions

Nitrofurantoin, 200mg, was administered orally to 11 subjects in an aqueous reference dispersion and in five suspensions having the same rheogram. Algin, carbomer, guar gum, methylcellulose, and colloidal magnesium aluminum silicate were the five suspending agents employed. Complexation was demonstrated by dialysis between nitrofurantoin and methylcellulose and between nitrofurantoin and carbomer; however, physiological availability was not altered by the interaction. The viscosity increase slowed absorption and urinary excretion, thus delaying the time of the maximum excretion rate without a decrease in bioavailability. A clinically acceptable urinary nitrofurantoin concentration was maintained for at least 2hr longer by a viscosity increase.

Optimization of Slow-Release Tablet Formulations: Containing Montmorillonite I. Properties of Tablets

AbstractSlow-release tablets containing 20%. sodium sul fathiazole and 30%. magnesium aluminum silicate were prepared by direct compression techniques. Dissolution studies indicated that tablet hardness exerted a negligible influence on drug release from the tablets. During the dissolution process the clay slowly swelled to form a gelatinous hydrated layer around the tablet matrix. At faster stirring speeds, friction between the dissolution basket and the tablet rapidly removed the hydrated boundary region and resulted in a more rapid dissolution rate of the sulfonamide. Faster rates of dissolution were seen in deionized water than in dilute acid since the clay hydrated more readily at the higher pit.

Increasing Dissolution Rates of Poorly Soluble Drugs by Adsorption to Montnorillonith

The surface adsorption of griseofulvin, indomethacin and prednisone to colloidal magnesium aluminum silicate was shown to markedly improve the dissolution rates of there hydrophobic and party soluble drugs. The rapid release of drug from the surface of the clay was due to the weak physical bonding between the two materials and to the swelling of the clay in aqueous media. The hydrophilic and swelling properties of the montmorillonite clay in aqueous media also helped to facilitate the wetting of hydro-phobic drug substances. The equilibrating solvents employed in the preparation of the griseofulvin-clay adsorbates caused a significant variance in the dissolution profiles of griseofulvin. This did not occur with indomethacin. Dramatic increases in dissolution rates were seen with the prednisone adsorbates and 100 percent of the drug was present in solution from the 1:4 ad-sorbate after four minutes.

Reliability and Durability of Ceramic Regenerators in a Gas Turbine

The two major causes of failure of ceramic regenerators in a gas turbine engine are excessive thermal stress and chemical attack of the basic ceramic material. Data are presented which show that regenerator life can be correlated on the basis of rim thermal-stress safety factor. Durability gains can be achieved through improved mechanical design of the regenerator system, as well as through improved ceramic materials. The test results from almost 50,000 hr of gas turbine operation on several different candidate materials and design concepts are also presented. Two materials, aluminum silicate and magnesium aluminum silicate, show promise of achieving the durability goals required for automotive and industrial turbine applications.

Fracture Strength and Thermal Shock Resistance of Thick And Thin-Wall Magnesium-Aluminum-Silicate Ceramic Heat Regenerators

Thin-wall regenerator cores offer the potential for higher effectiveness than comparable thick-wall cores. The fracture strength of magnesium-aluminum-silicate (MAS) ceramic heat-exchanger cores with wall thickness of 0.083 mm (0.003 in.) and 0.160 mm (0.006 in.) are compared. Thermal shock resistance calculations for these cores are also presented.

The effect of attapulgite and charcoal on enterotoxicity of vibrio cholerae and Escherichia coli enterotoxins in rabbits

Vibrio cholerae and certain strains of Escherichia coli produce heat-labile enterotoxins which play a significant role in the pathogenesis of the intestinal disease. Activated attapulgite, a heated magnesium aluminum silicate, was previously shown to prevent the toxic effects of endotoxin. The present study has revealed that this drug inhibits the toxic effects of cholera and E. coli enterotoxins in the intestinal loop of rabbits, when toxin and attapulgite are pre-incubated prior to injection. Up to 50 to 100 minimal effective doses are inhibited. Attapulgite is effective also when injected separately, albeit simultaneously, into the intestinal loops, but not when administered after the toxin. Since supernates of toxinattapulgite mixtures are non-toxic, it is postulated that attapulgite acts by adsorption and that the attached enterotoxin is no longer toxic to the rabbit intestine. The previously reported effect of charcoal on V. cholerae enterotoxin paralleling that of attapulgite, was confirmed. In contrast to the effects of these absorbents on isolated toxin, both failed to prevent enterotoxicity in the rabbit model of an enterotoxin-producing strain of E. coli.

Correlation of Absorption of Sulfamethazine Boluses with Dissolution Using a New Dissolution Apparatus for Veterinary Tablets

A rotating-basket apparatus for dissolution testing of veterinary bolus tablets was designed and constructed. Sulfamethazine boluses containing different disintegrating agents were evaluated in vitro and by blood level data following administration to cattle. The dissolution t50 and various pharmacokinetic parameters showed directly compressible starch and carboxymethylstarch to be the most effective disintegrants in the concentrations employed while magnesium aluminum silicate and microcrystalline cellulose were about equal but less effective than the previous disintegrants. A bolus formulation containing no disintegrant gave even less satisfactory results. A correlation was established between the dissolution t50 and the time to peak plasma level and also between the t50 and the area under the plasma-time curve for the first 36hr.

Influence of Monovalent and Divalent Electrolytes on Sorption of Neomycin Sulfate to Attapulgite and Montmorillonite Clays

Langmuir isotherms for the adsorption of neomycin sulfate to clays such as attapulgite, bentonite, and magnesium aluminum silicate were constructed. Monovalent and divalent cations were investigated for their influence on the formation of neomycin‐clay adsorbates and the resulting equilibrium concentration in a neomycin solution. Divalent magnesium ions were more effective in displacing the antibiotic from each clay than were monovalent sodium ions. Ions present in the GI fluid might increase the bio‐availability of neomycin from such neomycin‐clay adsorbates.

Alterations in Absorption of Dicumarol by Various Excipient Materials

A plasma level study was conducted in dogs to determine the effects of various excipient materials on the absorption of dicumarol. The drug was combined with the excipients by an equilibration process and administered orally. Plasma concentrations of dicumarol after administration with excipients were compared to control levels produced by the drug given alone. Significant differences in the plasma levels of dicumarol were observed with six of the 10 excipients used in the study. Significantly higher plasma levels (up to 180% of control values) were observed when dicumarol was administered with magnesium oxide or hydroxide. This effect may be due to chelate formation because the magnesium chelate of dicumarol produced higher plasma levels of dicumarol than the drug administered alone. Dicumarol administration with talc, colloidal magnesium aluminum silicate, aluminum hydroxide, or starch resulted in significantly lower plasma levels of the drug. It is suggested that these types of interactions may be an explanation for differences in the bioavailability of dicumarol from different dosage formulations.

Changes in Physicochemical Properties of Artificial Magnesium Aluminum Silicate by Hydrothermal Treating

In view of the fact that, as evidenced by the result of the antacid activity test, the artificial magnesium aluminum silicate prepared by hydrothermal treating has failed to equal its co-precipitated substance in neutralizing velocity and in activation energy of reaction with 0.1N-HCl, it is the aim of the present paper to investigate the changes in physicochemical properties of artificial magnesium aluminum silicate prepared by hydrothermal treating. Scarecely have hitherto studies been made of the kind of factors of changes in hydrothermal treating, such as the durability of antacids, bonding state and surface chemistry.As the result of differential radial distribution analysis shows there is but small variation from the specimens used in the hydrothermal treating to the co-precipitated specimens, and this variation is not considered to have much to do with durability. The authors have paid attention to the physicochemical properties of surface as main factors, and conducted measurements of the differential thermal analysis, of the surface area and of the amount of oil absorption in order to examine main factors of indicating durability at hydrothermal treating samples.It is concluded that the durability is influenced by the weak bonding state, and the surface properties mainly by such as the surface area, the hydrophilic property and the hydration structure.

Applications of the Montmorillonites in Tablet Making

The montmorillonites were studied for their use as disintegrants, binders, and lubricants for the manufacture of compressed tablets. It was found that the clays, although traditionally believed to be inert materials, agglomerated with several macro-molecules commonly used as tablet binders. When added dry to prepared granulations, magnesium aluminum silicate F was an excellent disintegrant which produced tablets disintegrating twice as fast as those containing an equal amount of cornstarch. Furthermore, the clays contained a lower moisture content and were more compressible than starch. However, the other grades of montmorillonite studied were less effective as disintegrating agents than starch, and wet granulation of the clays with the diluents substantially decreased the effectiveness of these materials as disintegrants.

An improved electric microcombustion furnace

( 1) Two serious weaknesses in one type of commercial electric microcombustion furnace have been corrected. Details of design of the component parts are described. ( 2) Dehydrated cordierite (hydrous aluminum magnesium silicate) can be used as a ceramic for furnace shells and Kanthal #13 as wire for heating elements. ( 3) By installing an inner lining for the furnace of 0.003-in. platinum foil, a firm temperature of 1025 °C. at the location of the sample can be quickly and repeatedly attained in daily operation. ( 4) Curves showing heating characteristics of the furnaces are included.

New Cerium Activated Scintillating Glasses

The synthesis of cerium activated scintillating glasses is being continued, and two new types have been developed. One of these, a magnesium aluminum borate, is similar to the alkali borate glasses reported previously and was made in an effort to provide a scintillating glass with the highest possible boron content in which a reasonable pulse height could be retained. Its pulse height with gamma excitation is 5.0 per cent of a Nal(Tl) crystal. The second glass developed is a lithium magnesium aluminum silicate. This glass has a pulse height 14.0 per cent of the Nal(Tl) crystal and is the most efficient material prepared in this program. Preliminary studies indicate that energy transfer between the base glass and the activator does occur, and that the efficiency of glass scintillators is not limited by the absence of energy transfer. mission.