Biomedical subjects

Khouloud A Alkhamis

Publications and source records attributed to Khouloud A Alkhamis.

9 recordsLinked to original sources

PubMed2006

Effect of surfactant on dissolution of spherical particles in micellar systems.

The influence of micelle-drug solubilization on the dissolution rate of monodisperse particles of benzocaine has been investigated. A model describing and predicting the initial dissolution rates of spherical particles was derived starting from the boundary layer theory. The dissolution rate of benzocaine spherical particles was determined in water and in solutions of sodium lauryl sulfate (SLS) under static conditions. The derived model was applied to the experimental data. The diffusion coefficients and the aqueous diffusion layer values were estimated from the experimental results and the aforementioned model. The diffusion coefficients and the boundary layer thickness values were also obtained experimentally from the rotating disk method and were used to predict the initial dissolution rates. Excellent correlations were obtained between the experimental and the calculated values at low micellar concentrations. However, obvious deviation was observed at high micellar concentrations. The results obtained from this study suggest that it is possible to predict the initial dissolution rates of monodisperse particles in micellar systems.

Algorithms↗

PubMed2006

Comparison between dehydration and desolvation kinetics of fluconazole monohydrate and fluconazole ethylacetate solvate using three different methods.

It was of interest to study the dehydration and the desolvation of fluconazole monohydrate and ethyl acetate solvate respectively and also to determine the kinetics of dehydration and desolvation using thermogravimetry (TGA). Fluconazole monohydrate and ethyl acetate solvate were prepared by crystallization in water and in ethyl acetate solvent respectively. The dehydration and the desolvation processes were characterized by differential scanning calorimetry, thermogravimetry, powder X-ray diffractometry, and Fourier transform infrared spectroscopy. The weight changes of the fluconazole monohydrate and ethyl acetate solvate samples were monitored by isothermal TGA. Kinetic analyses of isothermal TGA data were done using model dependent and model independent methods. Various heating rates were also employed in different TGA samples, in order to apply the Ozawa method to determine the kinetic parameters. Eighteen solid-state reaction models were used to interpret the isothermal TGA experiments. Based on statistics, the three-dimensional phase boundary reaction model provided the best fit of the monohydrate data while the three-dimensional diffusion model provided the best fit for the ethyl acetate solvate data. The activation energy (E(a)) values derived from rate constants of the aforementioned models were 90 +/- 11 and 153 +/- 11 kJ/mol for fluconazole monohydrate and ethyl acetate solvate respectively. Model independent analysis and the Ozawa method were also applied to the experimental results. Based on the results obtained from the model dependent, model independent and the Ozawa method, the mechanisms of the dehydration and the desolvation were determined.

Acetates↗

PubMed2004

Preparation and crystal characterization of a polymorph, a monohydrate, and an ethyl acetate solvate of the antifungal fluconazole.

The preparation and solid-state characterization of three crystalline modifications of the antifungal agent fluconazole [2-(2,4-difluorophenyl)-1,3-bis-(1H-124-triazol-1-yl)-propan-2-ol] are reported. Recrystallization of fluconazole from propan-2-ol yielded a polymorph (Form III), whereas the solvents water and ethyl acetate yielded the solvated products fluconazole monohydrate and fluconazole. (ethyl acetate)(0.25), respectively. These species were analyzed by thermogravimetry (TGA), differential scanning calorimetry (DSC), FTIR spectroscopy, powder X-ray diffractometry (PXRD), and single crystal X-ray diffraction. Availability of the hitherto unknown crystal structures facilitated interpretation of the thermal data and clarified previous findings relating to the polymorphism of this compound. Fluconazole was found to exist as a centrosymmetric hydrogen bonded dimer in Form III. For the solvated phases, the solvent locations within the drug host matrices were established as isolated sites for water molecules and constricted channels for ethyl acetate molecules. Desolvation of the monohydrate and ethyl acetate solvate yielded polymorphic Form I. Reference PXRD patterns computed from the refined single-crystal X-ray data for the title compounds are presented.

Acetates↗

PubMed2003

Study of the solubilization of gliclazide by aqueous micellar solutions.

It was of interest to increase the solubility of gliclazide in aqueous media. Therefore, solubilization of gliclazide in a variety of surfactants was investigated. Anionic and cationic surfactants exhibited dramatic solubilizing ability for gliclazide, whereas nonionic surfactants showed significantly lower solubilizing ability. It was found that gliclazide solubility increases with increasing the carbon chain length of cationic surfactants and decreases with increasing the carbon chain length of anionic surfactants. The solubilization data were analyzed on the basis of a pseudo-phase model with gliclazide exhibiting moderate partition coefficients into the micellar phase. The possible sites of solubilization of gliclazide in the micelle were examined by studying the effect of NaCl on solubilization and by comparing the absorption spectra of gliclazide in different solvents. The results obtained from these two experiments indicated that gliclazide is solubilized mainly in the inner core of the cationic surfactant micelles and in the outer regions of the anionic surfactant micelles.

Gliclazide↗

PubMed2003

Prediction of the adsorption of diazepam by activated carbon in aqueous media.

Adsorption isotherms for the diazepam-activated carbon system in simulated intestinal fluid (SIF), without pancreatin, and in SIF with different percentages of ethanol were determined as were the solubilities of diazepam in SIF and in SIF with different percentages of ethanol. The surface area of the activated carbon was also evaluated. The results from the experimental work provided information on the relationship between adsorption and solubility. An excellent logarithmic relationship was observed between the adsorption affinity and the solubility of diazepam in the ethanol-SIF mixtures. This relationship was explained by a linear relationship between the differential free energy of displacement and the differential free energy of solution. Excellent correlations were also observed between the amounts of diazepam adsorbed by activated carbon and the solubilities of diazepam in the ethanol-SIF mixtures. This relationship was used to predict the complete isotherm, which was in excellent agreement with the experimental work.

Adsorption↗

PubMed2003

The application of the convective diffusion model and the film equilibrium model to surfactant-facilitated dissolution of gliclazide.

Gliclazide is practically insoluble in water, and has low dissolution rate. Therefore, it was of interest to improve its dissolution rate using anionic and cationic surfactants. The intrinsic dissolution rates of gliclazide in solutions of sodium dodecyl sulfate (SDS) and in solutions of tetradecyltrimethyl ammonium bromide (TDTMAB) were measured using the rotating disk method to study the convective diffusion transport of drug-loaded micelles. Two different approaches were applied to the experimental data; the convective diffusion model and the film equilibrium model. The two approaches are based on the same fundamental assumptions differing only in their interpretation of the diffusional boundary layer. The results obtained from the film equilibrium model were less satisfactory, and in case of TDTMAB the model was inapplicable (negative diffusion coefficient). While excellent results were obtained from the convective diffusion model. The free solute diffusion coefficient (D(s)) obtained experimentally was 2.47 x 10(-5) cm(2)/s, and the diffusion coefficient of the drug-loaded SDS micelle (D(sm)) estimated was 1.74 x 10(-6) cm(2)/s. The drug-loaded SDS micelle radius was 14 A. The thickness of the diffusional boundary layer was 54 and 22 microm for the free solute and the drug-loaded SDS micelle, respectively. TDTMAB showed lower effect in improving the dissolution rate of gliclazide than SDS. The drug-loaded TDTMAB micelle diffusion coefficient was 1.03 x 10(-6) cm(2)/s. The radius of the drug-loaded TDTMAB micelle and the boundary layer thickness were 24 A and 19 microm, respectively.

Diffusion↗

PubMed2003

Study of multiple-component adsorption on the surface of activated carbon using a model system of benzyl alcohol and phenobarbital.

The purpose of this work was to characterize the surface of activated carbon and to study the specificity of interactions using multicomponent adsorption. The competition between phenobarbital and benzyl alcohol was studied by conducting multicomponent-adsorption experiments. Benzyl alcohol and phenobarbital were combined to form a bisolute system. The adsorption of the bisolute system from simulated intestinal fluid (without pancreatin) by activated carbon was studied by using the rotating bottle method. The concentrations, both before and after the attainment of equilibrium, were determined with the aid of an HPLC system using a reversed-phase column. The modified competitive Langmuir-like model was fit to the data. A good correlation was obtained between the experimental and the calculated data, which indicates that benzyl alcohol and phenobarbital are competing for the same binding sites. The competition between benzyl alcohol and phenobarbital was not expected, and it suggests that benzyl alcohol is not interacting with the site having the theoretically highest enthalpy of interaction (carbonyl group on the activated carbon surface), due to the blockage of this site by the solvent (water). This unexpected result also indicates that the hydroxyl group is likely to be the most important group when the adsorption occurs from aqueous solution.

Adsorption↗

PubMed2002

Solid-state characterization of fluconazole.

Two polymorphs and three solvates of fluconazole were isolated and characterized by x-ray powder diffractometry, IR spectroscopy, differential scanning calorimetry (DSC), thermogravimetry, and their dissolution rates. The different forms were prepared by crystallization of the original powder in different solvents at different cooling rates. X-ray diffraction patterns of the five solid modifications exhibited substantial differences in both the intensity and position of the peaks. FTIR spectra of the five different solid-state modifications also exhibited differences in the peaks' positions and intensities. DSC thermogram of anhydrate form I showed a single melting point at 139.2 degrees C. Anhydrate form II showed two endothermic peaks at 136.5 and 139.2 degrees C and one exothermic peak in between. The DSC thermogram of acetone 1/4 solvate exhibited two endothermic peaks at 75.5 and 139.2 degrees C. Benzene 1/7 solvate exhibited two endothermic peaks at 131.5 and 138.8 degrees C. Hydrate E exhibited two endothermic peaks at 102.7 and 139.2 degrees C. The DSC thermogram of anhydrate form II showed that this form is sensitive to the application of a mechanical force. The solubility study showed that anhydrate form II and acetone 1/4 solvate have higher solubilities than anhydrate form I while benzene 1/7 solvate and monohydrate have lower solubilities than anhydrate form I. The intrinsic dissolution study confirmed these results.

Fluconazole↗

PubMed2002

Prediction of adsorption from multicomponent solutions by activated carbon using single-solute parameters. Part II--Proposed equation.

Prediction of multicomponent adsorption is still one of the most challenging problems in the adsorption field. Many models have been proposed and employed to obtain multicomponent isotherms from single-component equilibrium data. However, most of these models were based on either unrealistic assumptions or on empirical equations with no apparent definition. The purpose of this investigation was to develop a multicomponent adsorption model based on a thermodynamically consistent equation, and to validate that model using experimental data. Three barbiturates--phenobarbital, mephobarbital, and primidone--were combined to form a ternary system. The adsorption of these barbiturates from simulated intestinal fluid (without pancreatin) by activated carbon was studied using the rotating bottle method. The concentrations, both before and after the attainment of equilibrium, were determined with a high-performance liquid chromatography system employing a reversed-phase column. The proposed equation and the competitive Langmuir-like equation were both fit to the data. A very good correlation was obtained between the experimental data and the calculated data using the proposed equation. The results obtained from the original competitive Langmuir-like model were less satisfactory. These results suggest that the proposed equation can successfully predict the trisolute isotherms of the barbituric acid derivatives employed in this study.

Adsorption↗