Biomedical subjects

S L Hem

Publications and source records attributed to S L Hem.

At least 73 records · Page 4Linked to original sources

PubMed1982

Evaluation of antacid suspensions containing aluminum hydroxide and magnesium hydroxide.

Liquid antacid suspensions containing aluminum hydroxide and magnesium hydroxide were evaluated for composition, antacid properties, and product quality. The equivalent aluminum oxide and magnesium hydroxide content was determined by chelatometric titration, and sodium content was determined by flame photometry. Antacid properties measured were acid-consuming capacity, antacid effectiveness (preliminary antacid test, acid-neutralizing capacity test), and pH-stat titration. Content uniformity, consistency of the antacid properties, and microbiological content were examined for each product. Data are presented for 36 products for which samples from four or more lots were obtained. The ratio of percentage of equivalent aluminum oxide to percentage of magnesium hydroxide ranged from 1:0.6 to 1:3.5; this range allows for selection of the desired balance between the laxative effect of magnesium hydroxide and the constipating effect of aluminum hydroxide. Based on a daily dose of 280 meq of antacid, the sodium content of the products tested ranged from less than 2% to approximately 45% of the 500 mg per day of sodium allowed in a sodium-restricted diet. The concept of bioavailability was related to the amount of the antacid reacting at pH 3, 37 degrees C during the estimated gastric residence time of 15 minutes. Antacid suspensions are available which will react almost completely (neutralizing greater than 90% of the theoretical quantity of acid) during the estimated gastric residence time. Approximately 4% of the samples contained unacceptable numbers of bacteria. An antacid suspension cannot be adequately evaluated by a single test; choice of a product should be based on an evaluation that integrates several characteristics including sodium content, time and volume required to neutralize a given amount of acid, and uniformity of content.

Aluminum Hydroxide↗

PubMed1981

Sepiolite, a potential excipient for drugs subject to oxidative degradation.

Sepiolite, a member of the fibrous mineral group of clays, is relatively free of surface ferric iron and does not accelerate significantly the oxidative degradation of hydrocortisone. The compatibility of sepiolite with drugs that can undergo oxidative degradation is in sharp contrast to the catalytic effect of attapulgite, another fibrous mineral, which contains a significant amount of surface ferric iron and which therefore accelerates oxidative degradation. Sepiolite adsorbs hydrocortisone by a weak adsorption mechanism, which was shown by IR spectroscopy to be chiefly due to hydrogen bonding. However, accelerated oxidative degradation of the adsorbed hydrocortisone does not occur. Maximum adsorption occurs at pH 7-8.5. Desorption occurs readily by washing with water. Sepiolite has similar rheological properties to attapulgite. The results of this study suggest that sepiolite may be useful as a pharmaceutical excipient for drugs that undergo oxidative degradation.

Adsorption↗

PubMed1981

Effect of adsorbed carbonate on surface charge characteristics and physical properties of aluminum hydroxide gel.

A titration procedure was used to determine the zero point of charge of a number of chloride-containing aluminum hydroxide gels and aluminum hydroxycarbonate gels. The surface charge characteristics of aluminum hydroxide gel were determined by both hydroxyls and the surface density of specifically adsorbed carbonate anion. The wide range of zero point of charge values reported for aluminum hydroxide is thought to be due to the presence of specifically adsorbed anions such as carbonate. The effect of ionic strength on the pH of aluminum hydroxide gel is important during washing since the ease of electrolyte removal is related to surface charge. Viscosity and sedimentation characteristics are related to the relationship between the zero point of charge and bulk pH. Maximum possibility was observed when the bulk pH was adjusted to the zero point of charge.

Adsorption↗

PubMed1981

Aluminum chlorohydrate I: Structure studies.

X-ray diffraction and IR and 27AI-NMR spectroscopy indicate that aluminum chlorohydrate is composed of a central aluminum in a tetrahedral configuration surrounded by 12 aluminum atoms in octahedral configuration. The complex, AI13O4(OH)24(H2O)7+12, is essentially spherical, with the +7 charge equally distributed on the surface. Seven chloride ions are associated with the complex as counterions. This structure is consistent with both the method of synthesis and the proposed mechanism of antiperspirant activity.

Aluminum Hydroxide↗

PubMed1981

Aluminum chlorohydrate II: Physicochemical properties.

Determination of the chloride content of aluminum chlorohydrate by a chloride-selective indicated that gamma Cl leads to 1. IR analysis demonstrated that chloride was exchanged readily by nitrate and that the IR bands of the anion were not perturbed significantly. Thus, chloride is believed to act as a counterion. A high positive charge is predicted based o the critical coagulation concentration of aluminum chlorohydrate and the stability of aluminum chlorohydrate to attack by protons, as demonstrated by pH-stat titration Potentiometric titration with sodium hydroxide showed adsorption of hydroxyl anions initially, but a higher pH than expected was observed at the end-point. This behavior is consistent with the Al13O4(OH)24(H2O)7+12 complex, which would adsorb hydroxyl anions initially and in which the central tetrahedral aluminum is shielded from the added hydroxyl anions. The reaction rate with ferron (8-hydroxy-7-iodo-5-quinolinesulfonic acid) suggests that the major species in aluminum chlorohydrate is a large aluminum poly-cation. A platey morphology for lyophilized, air-dried, and spray-dried aluminum chlorohydrate was observed by scanning electron microscopy. The platey appearance is consistent with the structure of Al13O4(OH)24(H2O)7+12 since the spherical nature and high uneven charge of the complex make stacking difficult.

Aluminum Hydroxide↗

PubMed1981

Aluminum chlorohydrate III: Conversion to aluminum hydroxide.

Bayerite, an aluminum hydroxide polymorph, readily forms when the hydroxyl to aluminum ratio of aluminum chlorohydrate is raised to 3 by titration with sodium hydroxide. Dilution of aluminum chlorhydrate solutions with water leads to the formation of gibbsite, another aluminum hydroxide polymorph. The mechanism of conversion in each instance is related to the structure of the Al13O4(OH)24(H2O)7+(12) complex.

Aluminum Hydroxide↗

PubMed1981

Investigation of gel structure of aluminum hydroxycarbonate gel using a tension cell.

A tension cell was designed to measure the gel structure of aluminum hydroxycarbonate gel. Equilibrium measurements of the total water outflow versus applied tension given insight into the rigidity of the gel structure. Dynamic measurements of the rate of outflow of water at various applied tensions yield the capillary conductivity of the gel, which is related to the apparent surface area, particle size, and porosity. An aluminum hydroxycarbonate gel with a high apparent viscosity exhibited an increase in viscosity upon aging at 25 degrees, which was accompanied by an increase in the equilibrium tension of the water phase, an increase in delta (-)GH2O, and a decrease in capillary conductivity. In contrast, the apparent viscosity of a low viscosity aluminum hydroxycarbonate gel, which was precipitated from the same reagents but with different precipitation temperature, pH, and stirring speed, exhibited a decrease in equilibrium water tension, a decrease in delta (-)GH2O, and an increase in capillary conductivity during aging at 25 degrees.

Aluminum Hydroxide↗

PubMed1981

Mechanism of interaction between polyols and aluminum hydroxide gel.

IR spectroscopy and changes in the rate of acid neutralization were used to study the interaction between various polyols and aluminum hydroxide. Hydrogen bonding is responsible for this interaction, although structural requirements limit the polyols that interact with aluminum hydroxide. Mannitol and sorbitol, both linear polyols, interacted with sulfate-containing aluminum hydroxide gel and aluminum hydroxycarbonate gel, while inositol, a cyclic polyol, did not interact. The adsorbed polyol has the favorable effect of inhibiting the polymerization reaction that occurs on aging and the negative effect of reducing the rate of acid neutralization. Thus, the specific polyol and concentration must be carefully selected to maximize the desired effect of stabilizing the gel structure. The presence of mannitol in the reaction medium during precipitation did not significantly enhance gel structure stability, probably because the mannitol was desorbed during the washing process as a consequence of the weak adsorption forces.

Adsorption↗

PubMed1980

Effect of polybasic acids on structure of aluminum hydroxycarbonate gel.

The effect of oxalic acid, citric acid, and their sodium salts on the structure of aluminum hydroxycarbonate gel was studied to illustrate the various mechanisms by which polybasic acids interact with aluminum hydroxycarbonate gel. Analysis of changes in the pH-stat titrigram, the carbonate to aluminum ratio, the aluminum content of the supernate following centrifugation, and the adsorption of the organic solute indicates that polybasic acids may: (a) partially neutralize the aluminum hydroxycarbonate gel by a general acid effect, (b) modify the aluminum hydroxycarbonate surface by adsorption of the anionic form of the polybasic acid, (c) extract aluminum by the formation of a soluble complex, and (d) lead to the precipitation of a new crystalline phase.

Aluminum Hydroxide↗

PubMed1980

Acid-base equilibria of tetracycline in sodium montmorillonite suspensions.

Changes in the partial molar free energy of the ionic species of tetracycline as a result of interaction with sodium-saturated montmorillonite were monitored by UV spectroscopic titrations. The stronger interaction between the clay and the protonated (H3T+) species relative to the zwitterionic (H2T0) species is responsible for the apparent displacement of pK1 in clay suspensions. The displacement of the first equilibrium favors in H3T+ species due to its stabilization by the negative clay surface. Little effect of the clay was observed on pK2 and pK3, because the ionic species of tetracycline associated with these equilibria (H2T0, HT-, and T2-) did not interact strongly with the negative clay surface. Therefore, the ionic species distribution of tetracycline in a sodium montmorillonite suspension is significantly different than that expected based on solution equilibria. The degree of equilibrium displacement depended on the accessibility of the negative charge at the clay surface. Fraction bound curves support the hypothesis that the clay surface causes a change in tetracycline equilibria. The H3T+ form of tetracycline was highly bound to the sodium montmorillonite, but little adsorption was observed for the H2T0 species.

Bentonite↗

PubMed1980

Characterization and adsorptive properties of pharmaceutical grade clays.

The adsorption of tetracycline by clays commonly used in pharmacy can be predicted if the identity and character of the commerical clay sample are established. X-ray diffraction. IR spectroscopy, and chemical analysis were used to identify the clay component and any nonclay diluents present in a series of commerical pharmaceutical grade clays. The major clay components were montmorillonite, hectorite, attapulgite, saponite, and kaolinite. The clay structure, the nature of the exchangeable cation, and the presence of nonclay components are important factors affecting the tetracycline-clay interaction. In general, clay structures with a high surface charge lead to a greater interaction with the protonated form of tetracycline, while interaction with the zwitterionic form of tetracycline occurs in clay structures with minimal surface charge. The presence of multivalent, exchangeable cations on the clay surface diminishes interaction with the protonated form of tetracycline. Nonclay components such as calcite and dolomite increase the interactions of the zwitterionic and anionic forms of tetracycline with the clay.

Adsorption↗

PubMed1980

Oxidative degradation of hydrocortisone in presence of attapulgite.

Degradation of hydrocortisone in attapulgite suspensions was monitored by high-pressure liquid chromatography and UV spectrophotometry. The rate of oxidative degration of hydrocortisone was accelerated significantly in the presence of attapulgite. In addition, degradation appeared to be composed of two apparent first-order reactions rather than the single apparent first-order degradation reaction observed for hydrocortisone solutions. However, the same degradation products were obtained in both hydrocortisone solutions and attapulgite suspensions, indicating that interaction with attapulgite did not alter the degradation pathway. Kinetic and adsorption studies suggested that hydrocortisone is adsorbed weakly by attapulgite and undergoes oxidative degradation, which is catalyzed by adsorbed iron oxides or hydroxides as well as by structural ferric iron at the clay surface. Since clay minerals generally contain surface ferric iron, the potentiala for accelerating the oxidative degradation of drugs should be considered whenever clays and drugs are combined.

Bentonite↗

PubMed1980

Potential of organic cation-saturated montmorillonite as treatment for poisoning by weak bases.

The preferential adsorption of the protonated form of weak bases by montmorillonite causes an increase in the pKeff of atrazine. The effect on the acid-base equilibrium of atrazine is related to the exchangeable cation on the surface of montmorillonite. The greatest effect was produced by the presence of 3-hydroxypropylammonium-saturated montmorillonite, which caused the pKeff of atrazine to increase 5.3 units to 6.9. This shift in pKeff causes the protonated form of atrazine to be the predominate species in the pH range encountered in the GI tract and should result in a high degree of adsorption of atrazine. Fraction-bound studies confirmed this hypothesis by demonstrating virtually complete absorption of atrazine by 3-hydroxypropylammonium-saturated montmorillonite up to pH 6. The fraction-bound studies also verified that protonated atrazine is adsorbed more completely by 3-hydroxypropylammonium-saturated montmorillonite than by bentonite USP or sodium-saturated montmorillonite. It is believed that saturation of the clay surface by an organic cation alters the surface environment of the clay, which results in enhanced adsorption of the protonated form of atrazine. The potential utility of montmorillonite saturated with an organic cation as an adsorbent for the emergency treatment of poisoning by weak bases is suggested.

Adsorption↗

PubMed1979

Carbon-13 magnetic resonance spectroscopy of drugs III: penicillins.

The natural abundance 13C-NMR spectra of a series of penicillins (penicillin V methyl ester, penicillin V, penicillin G, methicillin, oxacillin, cloxacillin, and dicloxacillin) were studied. The chemical shifts were assigned using the pulse Fourier transform technique with the aid of long-range carbon-13 hydrogen coupling. The previous assignments of pencillin V methyl ester were revised.

Carbon Isotopes↗

PubMed1979

Interaction of digoxin and montmorillonite: mechanism of adsorption and degradation.

IR, X-ray diffraction, and absorption studies showed that digoxin is adsorbed onto montmorillonite by a reversible adsorption mechanism at pH 2 and 6. Degradation studies indicated abnormally high acid hydrolysis rates for digoxin interacted with montmorillonite. Accelerated digoxin degradation is attributed to the ability of the clay surface to concentrate both digoxin and protons. The effective pH at the clay surface appeared to be 1.5 pH unites lower than the bulk suspension pH. Bisdigoxigenin was the major adsorbed degradation product. A similar catalytic effect also may occur with other neutral drugs that degrade by acid hydrolysis and should be considered in the formulation of clay-containing drug products or their coadministration with other drugs.

Adsorption↗

PubMed1979

Effect of interaction of aluminum hydroxycarbonate gel and magnesium hydroxide gel on acid neutralization.

Acid neutralization by mixtures of aluminum hydroxycarbonate gel and magnesium hydroxide gel differs from the sum of the acid neutralization of each gel. Acid neutralization by magnesium hydroxide gel in the mixture is not observed until after a substantial portion of the aluminum hydroxycarbonate gel has reacted with acid, even though magnesium hydroxide gel is the faster reacting of the two gels. It is hypothesized that amorphous aluminum hydroxycarbonate forms a coating on the crystalline magnesium hydroxide particles due to electrostatic attraction. This coating prevents protons from reaching the highly reactive magnesium hydroxide until the coating is dissolved by the acid neutralization of aluminum hydroxycarbonate.

Acids↗

PubMed1978

Demonstration of penicillamine as a product in benzylpenicillenic acid degradation in neutral media using differential pulse polarography.

During the study of the temporal changes of benzylpenicillenic acid in aqueous buffers using differential pulse polarography, penicillamine was found to be a degradation product at neutral pH. Since this result was not previously reported, the effects of pH and buffer concentration on penicillamine formation were investigated. The amount of penicillamine produced was greatest under conditions producing maximum benzylpenicillenic acid stability. Penicillamine was not obtained from benzylpenicilloic acid, the reported degradation product of benzylpenicillenic acid at neutral pH. Penicillamine also was detected in penicillin G solutions of neutral pH. Therefore, it is suggested that penicillamine found in penicillin G solutions arises from benzylpenicillenic acid degradation which, in turn, is produced from penicillin G isomerization. A pathway is proposed to show that penicillamine originates from the UV-absorbing isomer of benzylpenicillenic acid.

Chemical Phenomena↗

PubMed1978

Structural survey of carbonate-containing antacids.

A series of carbonate-containing antacids was examined by IR and X-ray analysis to establish the role of carbonate and to compare the structure of the antacids to naturally occurring carbonate minerals. Based on IR analysis, the relative degree of perturbation of carbonate increases in the order calcium carbonate, carbonate-containing aluminum hydroxide gel, and dihydroxyaluminum sodium carbonate. The crystalline carbonate-containing antacids were poorly organized forms of the minerals calcite, CaCO3; dawsonite, NaAl(OH)2CO3; and hydrotalcite, Mg6Al2CO3(OH)16-4H2O. Amorphous carbonate-containing aluminum hydroxide gel can be classified mineralogically as amorphous aluminum hydroxycarbonate. IR and X-ray evidence indicates that magaldrate has a hydrotalcite-like structure with sulfate as the major interlayer anion and carbonate also present in the interlayer space.

Aluminum Hydroxide↗