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F Alhaique

Publications and source records attributed to F Alhaique.

At least 19 recordsLinked to original sources
PubMed2003

Scleroglucan/borax: characterization of a novel hydrogel system suitable for drug delivery.

A new hydrogel, with scleroglucan using borax as a crosslinker, has been prepared. The physical gel has been loaded with a model molecule (theophylline) and the release of the drug from the gel was evaluated. The same system was used to prepare tablets and the delivery of theophylline in different environmental conditions (HCl and SIF) was determined. A recent theoretical approach has been applied to the dissolution profiles obtained from the tablets and a satisfactory agreement has been found with the experimental data. Furthermore, the diffusion coefficient of the model molecule was evaluated according to a suitable strategy that was tested on two set of data obtained with different set-ups (permeation and diffusion experiments). A simplified mathematical approach allows to reduce the two-dimensional problem of the Fick's second law in a one-dimensional system leading to a much easier handling of the data without loosing the accuracy of the original problem in two dimensions. The characterization of the gel has been also carried out following the kinetics of swelling in terms of water uptake.

Borates↗
PubMed2001

Low-degree oxidized scleroglucan and its hydrogel.

A controlled oxidation of scleroglucan was performed with sodium periodate to prepare aldehyde derivatives (scleraldehyde) with a low degree of oxidation (10 and 20%), which were utilized for crosslinking reactions with hexamethylenediamine. The structural characterization of scleraldehydes and their corresponding hydrogels was attempted by small-angle X-ray scattering (SAXS). While scleraldehyde with a higher degree of oxidation (> or = 50%), according to an earlier research, was found to disentangle into single chains as the degree of oxidation increases; scleroglucan bearing a low percentage of aldehydic groups (up to 20%) retains mainly the conformation of the natural polysaccharide, thus the system can be represented as composed of triple helices with only minor disentanglements at the sites where the aldehyde groups are present. The hydrogel prepared from scleraldehyde with a low degree of oxidation is brittle and fragmented, in contrast to the elastic/homogeneous hydrogel earlier prepared from scleraldehyde with a high degree of oxidation. The hydrogel from scleraldehyde with a low degree of oxidation was found to possess a network structure that consisted mostly of the triple helices crosslinked in specific points where the triple helices are disentangled into single chains because of the presence of the aldehyde groups.

Aldehydes↗
PubMed2001

A crosslinked system from scleroglucan derivative: preparation and characterization.

Matrices obtained by a crosslinking reaction between the polycarboxylated derivative of scleroglucan (sclerox) and 1,6-hexanedibromide have been prepared and characterized. Different ratios between the alkane dihalide and sclerox yielded products with different properties. Water uptake by the hydrogel with a low degree of crosslinking was remarkably affected by ionic strength. The determination of the crosslink density is led by simultaneously solving two Flory equilibrium equations referring to two different conditions characterized by the presence or the absence of a salt in the swelling agent. Moreover, the swelling kinetics was studied by means of a recently proposed model. Finally, the permeation of two model molecules (theophylline and polystyrene sulphonate-sodium salt) through the hydrogels was evaluated.

Cross-Linking Reagents↗
PubMed2001

Development of a profitable procedure for the extraction of 2-H-1-benzopyran-2-one (coumarin) from Mikania glomerata.

This report deals with a new procedure suitable for the extraction of coumarin 1 from Mikania glomerata. The aim of this investigation is to obtain this compound in an economically profitable way, taking into account the yield of its extraction, the cost, and the time of the overall process. Fresh and dried plants collected in several areas of the State of Rio de Janeiro were used, and seasonal effects on coumarin content were studied. Obtained results indicated that extraction with a 1% (w/v) NaOH solution, under appropriate conditions, allows a simple and complete recovery of the desired product and that the best yields were obtained with the fresh aerial parts of the plant. Season and area of harvesting effects have also been studied.

Costs and Cost Analysis↗
PubMed1999

Novel hydrogel system from scleroglucan: synthesis and characterization.

New hydrogels obtained by a crosslinking reaction between the polycarboxylated derivative of scleroglucan (sclerox) and 1, 6-hexanedibromide have been prepared and characterized. Different ratios between the alkane dihalide and sclerox yielded products with appreciably different properties. Water uptake by the hydrogel with a low degree of crosslinking was remarkably affected by ionic strength. The diffusion of a model molecule (theophylline) through the swelled crosslinked polymers was studied and the theoretical analysis leading to the calculation of permeability coefficients in different environmental conditions is reported. Tablets prepared with one of the new hydrogels behaved as swellable monolithic systems suitable for sustained drug release.

Bromides↗
PubMed1999

Effects of surfactants on the spectral behaviour of calcein (II): a method of evaluation.

The spectral behavior of calcein, a water-soluble self quenching fluorescent marker often used in biomedical analysis, can be considerably affected by the presence of surfactants. With this study we intend to obtain further information on the photophysical properties of calcein, in the presence of surfactants and in the concentration range commonly used to investigate the release of such marker from vesicle dispersions. The experiments were carried out both in water and in a physiological buffer (HEPES, pH 7.5), in the presence of Triton X-100, sodium dodecyl sulphate and centyltrimethylammonium bromide, both below and above their critical micelle concentration (c.m.c.). The obtained results confirm that calcein fluorescence can be affected by the presence of surfactants. Thus, environmental conditions must always be carefully checked for the actual quantitative evaluation of this dye. Furthermore, this study sheds some light on the nature and mechanism of calcein quenching.

Cetrimonium↗
PubMed1998

A novel co-crosslinked polysaccharide: studies for a controlled delivery matrix.

The formulation of a new controlled delivery system, based on a novel type of matrix obtained by the chemical reaction carried out in an aqueous medium on a mixed physical gel of gellan and scleroglucan, is described in this paper. The preparation yielded a new co-crosslinked polysaccharide (CCP) hydrogel, bearing carboxylic groups, that showed a sustained release behaviour that can be modulated by means of calcium ions. For the characterization of CCP, diffusion experiments through the swelled hydrogel were carried out in different environmental conditions and the release from tablets prepared with CCP and a model drug was evaluated. The addition of CaCl2 in the formulation of the dosage forms allowed a further marked reduction in delivery rate to be obtained; this effect is to be related to the free ionized carboxylic groups still present in the gellan moiety of CCP. The different behaviour of Ca+2 and Na+ ions is discussed.

Calcium↗
PubMed1997

Effects of in-vitro activity of miconazole and ketoconazole in phospholipid formulations.

Antifungal agents are often used in liposomal formulations in order to improve their pharmacological activity, but how vesicle inclusion can actually affect this is still not fully understood. We report here the results obtained from evaluation of the in-vitro activity against Candida albicans ATCC E10231 of miconazole and ketoconazole in various vesicular and non-vesicular preparations, obtained from egg and soya phospholipids, using time-kill curves. In most cases inclusion of miconazole or ketoconazole in liposomes led to a delayed and decreased activity of the drugs, with detectable differences among the various phospholipid concentrations and different liposomal preparations (small unilamellar vesicle, liposomes, multilamellar aggregates and broken liposomal structures). The results obtained may be helpful in the study of new preparations of antifungal agents entrapped in liposomal structures.

Antifungal Agents↗
PubMed1996

Gellan in sustained release formulations: preparation of gel capsules and release studies.

The ability of gellan to form gels in the presence of calcium ions enabled us to prepare capsules by gelation of this polysaccharide around a core containing starch, calcium chloride and a model drug. Release from the dried capsules was studied in vitro by means of the rotating basket technique (USP) in different environmental conditions (distilled water, pH = 2.0, pH = 6.8) and the effects of the presence of increasing amounts of drug in the formulation were also investigated. The behaviour of the gellan capsules was compared with that of beads prepared with the same polysaccharide but containing different additives. Results obtained indicate that gellan is suitable for the formulation of sustained release capsules and that solvent uptake by the dried capsules is most likely the main factor capable of affecting the rate of delivery from the tested preparations.

Calcium Chloride↗
PubMed1994

Effects of surfactants on the spectral behaviour of calcein.

The spectral behaviour of calcein, a water-soluble self-quenching molecule that is often used as a marker in biomedical analysis, can be considerably affected by the presence of surfactants. The aim of this work was to investigate the spectral properties of calcein under conditions that are particularly significant in liposome studies. For this purpose the fluorescence and absorbance of this dye were determined in solutions of ionic and non-ionic surfactants (cetyltrimethylammonium bromide, sodium dodecyl sulphate and Triton X-100), at different concentrations below and above their critical micelle concentrations (c.m.c.) as well as in the presence of phospholipids in the form of liposomes and/or mixed micelles. Cationic surfactants induced changes in lambda max, absorbance and fluorescence but these changes were less noticeable in the phospholipid dispersions. The anionic and the non-ionic surfactants induced mainly changes in fluorescence intensity.

Cetrimonium↗
PubMed1990

Scleroglucan sustained release oral preparations. Part II. Effects of additives.

Swelling and diffusion experiments, performed in vitro with tablets prepared with scleroglucan and several hydrophilic and hydrophobic additives, indicate that it is possible to modulate drug delivery from the matrix by appropriate choice of the nature and amount of the additive. The additives in the formulations may affect the mechanisms (zero order, diffusion, erosion) involved in the release of drugs from the dosage forms.

Chemistry, Pharmaceutical↗
PubMed1989

Scleroglucan sustained-release oral preparations. Part I. In vitro experiments.

Experiments performed in vitro with tablets and capsules indicate that the fungal polysaccharide scleroglucan is suitable for the formulation of sustained-release, oral dosage forms. Delivery of model drugs from the non-disintegrating matrix was studied in solutions buffered at different pH values. The effect on drug release of drug concentration, the physico-chemical properties of the drug, and the compression force used in the preparation of the matrix are reported, and the possible mechanisms of release are discussed.

Capsules↗
PubMed1987

Prevention of molecular self-association by sodium salicylate: effect on insulin and 6-carboxyfluorescein.

The effect of sodium salicylate on the concentration-dependent self-association of insulin and 6-carboxyfluorescein (CF), as expressed by metachromasy, fluorescence, and changes in aqueous solubility, was learned. By decreasing the CF concentration from 12 to 0.48 microgram.ml-1, lambda max peaks shift from the shorter wavelengths (451, 474 nm), indicating the presence of oligomers, toward the monomer wavelength region (484 nm). Sodium salicylate shifts the peaks of a 12 micrograms.mL-1 CF solution towards the monomer region, eliminating the peak at the lower wavelengths and generating a spectrum with one peak at 490 nm, the effect being concentration dependent. The fluorescence of insulin and CF solutions increases with their concentration. Quenching of these solutions was observed, up to complete elimination of fluorescence, when various concentrations of salicylate were added. The water solubility of both molecules, CF and insulin, was considerably increased with the addition of increasing concentrations of salicylate to the solutions: at 37 degrees C, 2.5 M sodium salicylate solution increases the CF solubility 532 times from 12.2 to 6.5 mg.mL-1, and 1.5 M salicylate increases the solubility of insulin 7875 times, thus an aqueous solution containing 630 mg.mL-1 of insulin may be prepared. The results obtained here, together with our previously reported data, indicate that the interference between sodium salicylate and drug self-association behavior, by increasing drug solubility, may substantially contribute to the improved drug bioavailability mediated by salicylate.

Chemistry, Pharmaceutical↗
PubMed1985

A possible pH-controlled drug delivery system based on a derivative of the polysaccharide scleroglucan.

Four carboxylated derivatives of scleroglucan have been obtained by oxidation, to different extents, of the glucopyranose side chains of the natural polysaccharide. The diffusion of model molecules through aqueous solutions of these new products was measured at various pH values. The reversible pH induced sol-gel transition of some of the polyelectrolyte solutions tested effects a remarkable variation in the diffusion rate of the permeating species; in this sense the most interesting polysaccharide appears to be the product with 70% oxidized glucopyranose moieties. The behaviour of scleroglucan and its derivatives has been compared with that of carboxymethylcellulose and the mechanism involved in drug permeation and release discussed. The possible application of one of the new products in controlled release formulations for oral use is also reported.

Delayed-Action Preparations↗
PubMed1985

Cholic acids/salts as barriers to diffusing species: effect of pH.

Bile acids have been absorbed on a microporous polypropylene membrane and the diffusion of ionic and non-ionic compounds through the barriers obtained has been studied at different pH values. Results indicate that permeation rates are affected by environmental pH conditions and an explanation of this behaviour is proposed. This study represents an approach for a pH-controlled drug delivery system.

Chenodeoxycholic Acid↗
PubMed1983

Swelling and binding effects in a polymeric microfiber model for controlled drug release.

The diffusion of model molecules from water dispersions of ethylenevinyl-N,N-diethylglycinate copolymer microfibers has been studied in different conditions. The influence of pH on diffusion rate has been related to water association and swelling effects following structural transitions induced in the copolymer by the acidic medium, rather than to difference in binding of the diffusing species to the macromolecule.

Benzoates↗