Solubilization and rate of dissolution of drugs in the presence of physiologic concentrations of lysolecithin

Molecular dynamics study on micelle-small molecule interactions: developing a strategy for an extensive comparison

Theoretical predictions of the solubilizing capacity of micelles and vesicles present in intestinal fluid are important for the development of new delivery techniques and bioavailability improvement. A balance between accuracy and computational cost is a key factor for an extensive study of numerous compounds in diverse environments. In this study, we aimed to determine an optimal molecular dynamics (MD) protocol to evaluate small-molecule interactions with micelles composed of bile salts and phospholipids. MD simulations were used to produce free energy profiles for three drug molecules (danazol, probucol, and prednisolone) and one surfactant molecule (sodium caprate) as a function of the distance from the colloid center of mass. To address the challenges associated with such tasks, we compared different simulation setups, including freely assembled colloids versus pre-organized spherical micelles, full free energy profiles versus only a few points of interest, and a coarse-grained model versus an all-atom model. Our findings demonstrate that combining these techniques is advantageous for achieving optimal performance and accuracy when evaluating the solubilization capacity of micelles. All-atom (AA) and coarse-grained (CG) umbrella sampling (US) simulations and point-wise free energy (FE) calculations were compared to their efficiency to computationally analyze the solubilization of active pharmaceutical ingredients in intestinal fluid colloids.

Wetting behavior of bile salt-lipid dispersions and dissolution media patterned after intestinal fluids

The wetting properties of bile salt-lipid solutions and dispersions patterned after the contents of the upper intestine in the fed and fasted states were evaluated using poly(methyl methacrylate) (PMMA) as a model substrate. The surface tension of the solutions and their contact angles on PMMA were measured. Media compositions for the intestinal fed and fasted states were estimated on the basis of physiologic data. The effect of various individual lipids and media composition was also evaluated relative to the adhesional, immersional, and spreading stages of wetting. In micellar systems, both the type and concentration of lipid present in the bile salt solution had an influence on wetting. The wetting of media patterned after gastrointestinal contents showed marked differences with respect to the fed or fasted state compositions. For the fed state compositions, alteration of the solution pH from 7.5 to 5.0 resulted in a significant change in wetting. The surface tension of the medium representative of the fasted state was 15 mN/m higher than that of the fed state. The wetting properties of the physiologically representative media formulated in this study were markedly different compared with other media proposed in the literature. Analysis of the wetting behavior of individual lipids as a function of concentration in bile salt solutions showed that they adsorb in a manner that progressively reduces the expected wetting of the surface. The results have implications for the design and formulation of both biorelevant and surfactant-based dissolution media.

Gastric juice as a dissolution medium: surface tension and pH

Aspirated gastric juice from eight patients was measured for surface tension, bile salt concentration and pH. Surface tension ranged between 35 and 45 mM/m, while pH was usually in the range 1-2 and bile salt concentrations were usually between 0 and 1 mM. No correlations were found between the three parameters. These findings suggest that the low surface tension of gastric juice cannot be attributed solely to refluxed bile salts. Once the source of the reduced surface tension is identified dissolution test media should be adjusted to represent these conditions.

Intestinal absorption of drugs. The influence of mixed micelles on on the disappearance kinetics of drugs from the small intestine of the rat

The solubilization of the hydrophilic drugs paracetamol and theophylline, and the lipophilic drugs dantrolene, griseofulvin and ketoconazole has been determined in mixed micellar aqueous dispersions composed of 10 mM taurocholate + 5 mM oleic acid. The solubilization of dantrolene and paracetamol has also been determined in aqueous (mixed) micellar dispersions of 1 g L-1 lysophosphatidyl-choline (LPC), or taurocholate/LPC. The influence of these (mixed) micelles on the absorption of the model drugs from solution was studied in the rat chronically isolated internal loop. Absorption kinetics of the drugs were evaluated on the basis of the disappearance rate of the drug dissolved in the perfusion medium in this loop. Absorption experiments with taurocholate/oleic acid in the perfusate resulted in a reduction of the disappearance rate for the lipophilic drugs and the hydrophilic drug theophylline. This could partly be ascribed to the decreased fraction of drug free in solution as a result of its micellar solubilization for dantrolene, griseofulvin and ketoconazole, but the decrease in the disappearance rate of theophylline was unexpected. Taurocholate/oleic acid, LPC and taurocholate/LPC micelles had no effect on the disappearance of paracetamol. The disappearance rate of dantrolene in the presence of LPC alone was not altered, in spite of the decreased fraction of the drug free in solution owing to its micellar solubilization. In contrast, taurocholate/LPC micelles caused a reduction in the rate of disappearance of dantrolene, as expected according to the phase-separation model. In-vitro, taurocholate and taurocholate/LPC reduced the molecular cohesion of porcine intestinal mucus, whereas LPC alone did not exhibit an effect on the gel structure of mucus.(ABSTRACT TRUNCATED AT 250 WORDS)

Mesure de la vitesse de dissolution pour l'amélioration et le contrôle de la qualité des médicaments

The main purpose of this presentation is to define the different situations in which dissolution tests are used. The criteria for choosing a method and the establishment of the experimental procedure depend on the research goal. Information concerning the dissolution medium (surfactants, enzymes, volume, de-aeration) confirms, disproves, or completes the classical recommendations.

Comparison of polyethylene glycol and polyoxyethylene stearate as excipients for solid dispersion systems of griseofulvin and tolbutamide II: dissolution and solubility studies

The effects of joining a long-chain ester group with the polyethylene glycol molecule were studied in solid dispersion systems by comparing the dissolution and solution properties of such systems prepared from polyethylene glycol 2000 with those prepared from the nontoxic, water-soluble, solid excipient polyoxyethylene 40 stearate. Solid dispersion systems of griseofulvin and tolbutamide were prepared by physical mixing, fusion, or coprecipitation from ethanol. The compacted dispersion systems dissolved by progressive erosion, releasing floccules of microcrystals. The released microcrystals of tolbutamide (3--10 micrometer) were smaller than the original drug particles (approximately 20 micrometer), but those of griseofulvin were of similar size to the original particles. In general, the rate of and extent of release of each drug were greater from polyoxyethylene 40 stearate than from polyethylene glycol 2000 dispersions. The aqueous solubility and dissolution rate of nondisintegrating disks of each pure drug increased only slightly in the presence of polyethylene glycol 2000 but increased considerably with increasing concentration of polyoxyethylene 40 stearate due to micellar solubilization. Thus, polyoxyethylene 40 stearate generally is superior to polyethylene glycol 2000 in promoting the dispersion of the drugs in solids, disintegration of the compacted solids, and solubilization of the drug during dissolution.

Effect of dioctyl sodium sulfosuccinate and poloxamer 188 on dissolution and intestinal absorption of sulfadiazine and sulfisoxazole in rats

The influence of two medicinal surfactants, poloxamer 188 and dioctyl sodium sulfosuccinate, on the dissolution of sulfisoxazole and sulfadiazine was investigated. A dramatic increase in the dissolution rate was observed at all surfactant concentrations. Drug absorption from the rat small intestine was also studied, and a significant but less dramatic increase was noted. Dissolution rate and absorption could be correlated only qualitatively. The two surfactants had no effect on the amount of sulfisoxazole excreted by the rat in 24 hr.

Bioavailability of micronized griseofulvin from corn oil-in-water emulsion, aqueous suspension, and commercial tablet dosage forms in humans

The purposes of this investigation were to determine and to compare the oral absorption characteristics of micronized griseofulvin (500 mg) after its administration to humans in the form of a corn oil-in-water emulsion containing dispersed drug, an aqueous suspension, and two different commercial tablets (A and B). The four dosage forms were administered in a random crossover fashion to five fasting subjects, and drug absorption was assessed from urinary excretion data for the major metabolite of the antibiotic (6-desmethylgriseofulvin). The drug was most rapidly, uniformly, and completely absorbed from the corn oil-in-water emulsion. As compared to either the aqueous suspension, Tablet A, or Tablet B, three- to fourfold increases in the maximum body levels and a twofold enhancement in the bioavailability of the antibiotic were observed after administration of the emulsion dosage form. A mechanism based on the ability of the linoleic and oleic acids liberated during the digestion of corn oil to inhibit GI motility and stimulate gallbladder evacuation may explain the marked enhancing effect of emulsified corn oil on griseofulvin absorption in humans. This new lipid-in-water emulsion dosage form of micronized griseofulvin appears to offer several clinical advantages in the treatment of fungal infections.

The solubilization of some local anaesthetic ester of p-aminobenzoic acid by lysophosphatidylcholine

The solubilization by lysophosphatidylcholine (LPC) of three n-alkyl esters of p-aminobenzoic acid has been studied. These esters have a local anaesthetic action. Quantitative studies show that the amount of compound solubilized is proportional to the LPC concentration and that solubilization increases in the order ethyl, n-propyl and n-butyl ester. 100MHz nmr studies indicate that the local anaesthetic esters are solubilized in the hydrocarbon interior of the LPC.

The effect of some non-ionic surfactants and a polyoxyethylene glycol on the dissolution rate of griseofulvin

Measurements of the dissolution rate of griseofulvin in water, four non-ionic surfactants, and a polyoxyethylene glycol have been made. These results are analysed in terms of a zero order rate constant (k1) for transfer of the drug from the crystal to the bulk of the solution, and a first order constant (k2) for the reverse process. Surfactants greatly increase the dissolution rate, increasing k1 and decreasing k2. Polyoxyethylene glycol is not so effective as the surfactants at increasing dissolution rates. In an attempt to interpret k1 and k2, it appears that both chemical and transport processes are involved in the dissolution, the presence of surfactant decreasing the energy change for transferring griseofulvin molecules from the crystal to the solution.

Solubilization of griseofulvin by nononic surfactants

Four nonionic surfactants, Me[CH2]15·[OCH2·CH2]xOH where x = 10, 22, 45 and 60, and polyoxyethylene glycols 200, 400 and 1000 increased the solubility of griseofulvin over its value in water. Cetomacrogol micelles solubilize two molecules of griseofulvin per micelle. The site of solubilization seems likely to be the polyoxyethylene part of the micelles. The partial molal heats and entropies of solution decrease as surfactant or polyoxyethylene glycol concentration is increased.