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PubMed1993

A modification of the extended Hildebrand approach to predict the solubility of structurally related drugs in solvent mixtures.

A modification of the extended Hildebrand equation is proposed to estimate the solubility of an organic drug in solvent mixtures. The equation accurately reproduces the solubility of four sulphonamides in dioxane-water mixtures without requiring the heat of fusion of the solute. A single equation is obtained for predicting the solubility of related drugs using the solubilities of the drugs in the pure solvents, dioxane and water, and solute-solvent interaction terms consisting of the solubility parameter, delta 2, of the solute and the solubility parameter, delta 1, and basic partial solubility parameter, delta 1b, of the solvent mixture. By this procedure a single equation was obtained to estimate the solubilities of three xanthines in dioxane-water and another equation to obtain the solubilities of four sulphonamides. The equation obtained for sulphonamides is able to predict the experimental solubilities of two parent compounds, sulphasomidine and sulphathiazole, and the solubilities of a drug of different structure, p-hydroxybenzoic acid. This suggests that the intermolecular solute-solvent interaction of sulphonamides and p-hydroxybenzoic acid are similar. The results indicate that the solubility behaviour of drugs having different structures may be modelled using a common equation provided that they show similar solute-solvent interactions.

Dioxanes↗

PubMed2002

Quantification of the soluble leptin receptor in human blood by ligand-mediated immunofunctional assay.

Panels of monoclonal antibodies (mAbs) were raised against recombinant human leptin and the recombinant human soluble leptin receptor. Using these mAbs, we established a ligand-mediated immunofunctional assay (LIFA) to quantify concentrations of the soluble leptin receptor, which has been shown to be a major binding protein for leptin in human serum. In performing the assay, a monoclonal antibody (mAb 2H6) against the soluble leptin receptor, which binds an epitope outside the leptin-binding site and equally recognizes both, free and leptin-occupied soluble leptin receptor, is used to capture the soluble leptin receptor on a microtiter plate. Recombinant human leptin is added to saturate all binding sites, and a biotinylated anti-leptin mAb (4D3) detects the amount of leptin (endogenous and exogenous) bound to the soluble leptin receptor. The same procedure, but without adding exogenous leptin, allows for measurement of the circulating endogenous leptin/soluble leptin receptor complexes. The LIFA assay has a linear working range of 0.5-200 microg/liter, intra- and interassay coefficients of variation ranged from 3.2-6.3% and from 5.2-7.9%, respectively. The assay has a linearity of 102.2 +/- 5.2% (mean +/- SD) and a recovery of 100.7 +/- 6.9%. Size-exclusion chromatography revealed that the assay measures a protein with a main peak eluted at 340 kDa. The soluble leptin receptor concentration (63.3 +/- 22.8 microg/liter (mean +/- SD), range 17.9-129.2 microg/liter, n = 43) in normal subjects (body mass index = 22.3 +/- 2.3 kg/m(2)) was not different from the concentration (54.4 +/- 19.8 microg/liter, range 23.7-104.8 microg/liter, n = 34, P > 0.05) found in obese subjects (body mass index = 40.9 +/- 15.7 kg/m(2)). However, the percentage of the total soluble leptin receptor complexed with endogenous leptin was significantly higher in obese subjects, compared with normal subjects (74.9% +/- 23.5% vs. 33.1% +/- 19.5%, P < 0.001). Higher serum leptin levels in obese subjects (38.4 +/- 23.7 microg/liter vs. 7.8 +/- 5.5 microg/liter in normal subjects, P < 0.001) together with comparable soluble leptin receptor levels result in a lower proportion of leptin bound to the soluble leptin receptor in obese subjects (19.3% +/- 19.4%, range 4.9-97.2%) than in normal subjects (39.0% +/- 22.5%, range 15.3-96.5%, P < 0.001). The development of this LIFA for the rapid and accurate quantification of total soluble leptin receptor and circulating leptin/soluble leptin receptor complexes provides a valuable tool for the further understanding of the role of leptin and its soluble receptor in health and disease.

Adult↗

PubMed2001

Analysis of the phase solubility diagram of a phenacetin/competitor/beta-cyclodextrin ternary system, involving competitive inclusion complexation.

The competitive inclusion complexations in the ternary phenacetin/competitors/beta-cyclodextrin (beta-CyD) systems were investigated by the solubility method, where m-bromobenzoic acid (m-BBA) and o-toluic acid (o-TA) were used as competitors. The solubility changes of the drug and competitors as a function of beta-CyD concentration in the ternary systems were formulated using their stability constants and intrinsic solubilities. The decrease in solubility of phenacetin by the addition of competitors could be quantitatively simulated by the formulation, when both drug and competitor give A(L) type solubility diagrams. On the other hand, when one of the guests gives a B(S) type solubility diagram, its solubility change was clearly reflected in that of the another guest, i.e., phenacetin gave an A(L) type solubility diagram in the binary phenacetin/beta-CyD system and o-TA gave a B(S) type diagram in the binary o-TA/beta-CyD system, but in the ternary phenacetin/o-TA/beta-CyD system, a new plateau region appeared in the original A(L) type diagram of phenacetin. This was explained by the solubilization theory of Higuchi and Connors. The solubility analysis of the ternary drug/competitor/CyD systems may be particularly useful for determination of the stability constant of a drug whose physicochemical and spectroscopic analyses are difficult, because they can be calculated by monitoring the solubility change of a competitor, without monitoring that of a drug. Furthermore, the present results suggest that attention should be paid to the type of the phase solubility diagram, as well as the magnitude of the stability constant and the solubility of the complex, for a rational formulation design of CyD complexes.

Cyclodextrins↗

PubMed1996

Solubility enhancement of a bisnaphthalimide tumoricidal agent, DMP 840, through complexation.

The purpose of this research was to enhance the aqueous solubility of DMP 840 by complexation with water-soluble and nontoxic agents, and to understand the nature of the interactions involved in complex formation using nuclear magnetic resonance (1H-NMR). The solubility of DMP 840 in water, saline, acetate buffers, and cosolvent mixtures was determined by high-performance liquid chromatography, and the effect of nicotinamide and pyridoxine concentrations on the solubility of DMP 840 was examined by the phase solubility method. 1H-NMR spectra were acquired in deuterated acetate buffer at 400 MHz on a Varian Unity-400 spectrometer. The aqueous solubility of DMP 840 was sensitive to the presence of chloride and acetate anions in solution, and did not improve in the presence of cosolvents. The use of the nontoxic and water-soluble complex-forming agents nicotinamide and pyridoxine, however, resulted in a linear increase in the aqueous solubility of DMP 840 with both ligands. The solubilization appears to be due to formation of 1:1 complexes between DMP 840 and the bioorganic ligands. The complexation constants were 15.57 M-1 for the DMP 840:nicotinamide complex and 13.36 M-1 for the DMP 840:pyridoxine complex. The NMR results indicate that the interaction is a result of vertical or plane-to-plane stacking and the complexation constants were in agreement with that obtained by phase solubility. The results suggest that the aqueous solubility of a poorly water soluble drug substance such as DMP 840 can be significantly enhanced by its complexation with water-soluble and nontoxic agents.

Antineoplastic Agents↗

PubMed2006

Solubilization behavior of a poorly soluble drug under combined use of surfactants and cosolvents.

The solubilization behavior of a poorly soluble model drug, phenytoin (PHT), under combined use of surfactants (sodium dodecyl sulfate (SDS), Tween 80) and cosolvents (dimethylacetoamide (DMA), ethanol, poly(ethylene glycol) 400 (PEG), glycerol) was examined. The solubility of PHT in the aqueous surfactant solutions increased linearly with increase of the surfactant concentration. The solubility of PHT in water-cosolvent mixtures roughly followed the log-linear model, which is widely accepted to explain the solubilization behavior of poorly soluble compounds in water-cosolvent mixtures, except for the case of glycerol, in which the solubility was minimal at 10% (w/v) of glycerol. When the cosolvents were added to the aqueous surfactant solutions, their effect on the solubility depended on the combination of the surfactant and the cosolvent. The most striking increase in solubility was observed with DMA, regardless of the type of surfactant. When ethanol was added, an increase in the solubility was observed with the Tween 80 solution, while a dramatic decrease was found with the SDS solution. The addition of glycerol or PEG to the surfactant solutions had only a minor impact on the solubility. These solubilization behaviors of PHT in the surfactant-cosolvent mixtures were partially explained by the solubility model introduced in our previous paper [Kawakami, K., Miyoshi, K., Ida, Y., 2004. Solubilization behavior of poorly soluble drugs with combined use of Gelucire 44/14 and cosolvent. J. Pharm. Sci. 93, 1471-1479]. Addition of the cosolvents to the surfactant solutions generally offered only a small advantage from the viewpoint of improving solubility because of the decrease in the solubilization capacity of the micelles.

Algorithms↗

PubMed1997

Soluble E-selectin as a marker of disease activity in atopic dermatitis.

BACKGROUND: Augmentation in the expression of adhesion molecules on endothelial cells can regulate leukocyte migration. These molecules are also shed into the circulation. The level of soluble adhesion molecules in the serum is known to reflect the degree of systemic inflammation, and this level can therefore be used as a marker of inflammation. OBJECTIVE: To elucidate whether soluble adhesion molecules can be used as the marker of disease severity in atopic dermatitis, we examined the levels of soluble E-selectin, soluble intercellular adhesion molecule-1, and soluble vascular cell adhesion molecule-1 and compared these levels with the patients' symptom scores and their total serum IgE levels. METHODS: Fifty-three patients with atopic dermatitis were studied. Soluble adhesion molecules were measured by ELISA. RESULTS: The level of soluble E-selectin was higher in patients with atopic dermatitis than in healthy control subjects (p < 0.01). Moreover, soluble E-selectin is correlated with disease severity (p < 0.01). Soluble E-selectin also reflected the changes in symptom scores. In contrast, there were no differences in soluble intercellular adhesion molecule-1 and soluble vascular cell adhesion molecule-1 between the patients and control subjects. CONCLUSION: Soluble E-selectin is a good marker of disease severity and of its activity in atopic dermatitis.

Adult↗

PubMed1995

Soluble human interleukin-6 receptor. Expression in insect cells, purification and characterization.

The extracellular domain of the human interleukin-6 (IL-6) receptor, comprising 339 amino acids following the signal peptide, has been expressed in baculovirus-infected insect cells (Sf158). When the soluble receptor secreted into the culture medium was purified by affinity chromatography, using IL-6 immobilized on Sepharose, 6 mg soluble receptor was isolated from 1 l conditioned medium of Sf158 suspension cultures. A molar absorption coefficient of 9.3 x 10(4) l.mol-1.cm-1 was calculated from the ultraviolet spectrum of the soluble IL-6 receptor. After SDS/PAGE and silver staining, an apparent molecular mass of 48 kDa was estimated for the purified protein. Deglycosylation with peptide N-glycosidase F resulted in an increase in electrophoretic mobility and a decrease in the apparent molecular mass from 48 kDa to about 41-44 kDa. As expected, the soluble human IL-6 receptor bound human 125I-labeled IL-6 with low affinity (Kd = 500 pM). Furthermore, the binding of soluble human IL-6 receptor to immobilized IL-6 was studied using real-time interaction analysis. The recombinant soluble receptor showed biological activity on HepG2 cells stably transfected with a cDNA coding for IL-6 (HepG2-IL-6 cells). Haptoglobin mRNA synthesis was induced by the soluble IL-6 receptor at concentrations as low as 10 ng/ml. Five monoclonal antibodies were generated. Two groups of antibodies were identified mapping to amino acids 1-67 and 68-143 of the soluble IL-6 receptor, respectively. The plasma clearance of soluble 125I-labeled IL-6 receptor in the absence and presence of IL-6 was studied in rats as a model system. The kinetics was biphasic. Soluble IL-6 receptor/IL-6 complexes were cleared more rapidly than the soluble receptor alone. Intravenously injected soluble 125I-labeled IL-6 receptor, as well as complexes with IL-6, rapidly accumulated in liver and to a lesser extent in skeletal muscle, skin and kidneys. Subsequently, the radioactivity appeared in the gut content.

Animals↗

PubMed1996

Soluble receptors and cytokine antagonists in human milk.

To determine whether human milk contained soluble receptors and cytokine antagonists that might contribute to its anti-inflammatory properties, ELISA and enzyme-amplified sensitivity immunoassay methods were used to quantitate soluble intercellular and vascular cell adhesion molecules, soluble E-selectin, soluble IL-6 receptor, IL-1 receptor antagonist, and soluble tumor necrosis factor-alpha (TNF-alpha) receptors I and II in human milk and colostrum. Soluble adhesion receptors (soluble intercellular and vascular cell adhesion molecules and soluble E-selectin) were present in colostrum at levels approximately equal to serum, whereas milk levels were significantly lower. Both colostrum and milk contained soluble IL-6 receptor, but the levels present were significantly lower than that reported for serum. The colostrum contents of IL-1 receptor antagonist (672 +/- 202 pg/mL), TNF-alpha receptor I (> 3703 +/- 305 pg/mL), and TNF-alpha receptor II (> 4507 +/- 770 pg/mL) were significantly elevated over serum/plasma levels. Milk levels of IL-1 receptor antagonist and TNF-alpha receptor I were also greater than serum/ plasma levels, but lower than colostrum levels. Examination of sequential milk specimens collected from seven women over a period of 2-6 mo showed that IL-1 receptor antagonist and TNF-alpha receptors I and II persisted throughout lactation. Column chromatographic fractionation of colostrum and milk demonstrated that soluble TNF-alpha receptors I and II had molecular sizes up to 60 kD, suggesting that they might be associated with other molecules. Antigen assays for TNF-alpha in colostrum and milk, as well as chromatographic fractionation experiments, showed that, although present, most TNF-alpha was not "free" in colostrum or milk, consistent with the observed content of soluble TNF-alpha receptors I and II. These studies demonstrate that human milk and colostrum contain soluble receptors and cytokine antagonists, materials which could contribute to their anti-inflammatory properties.

Antigens, CD↗

PubMed2000

[Evaluation of restenosis by serum levels of soluble Fas, Fas ligand and nuclear matrix protein before and after coronary intervention].

Serum levels of soluble Fas, soluble Fas ligand, and nuclear matrix protein (NMP) were measured in 38 patients with ischemic heart disease before and after coronary angiography or coronary intervention. Serum levels of soluble Fas, soluble Fas ligand and NMP were determined by enzyme-linked immunosorbent assay. Patients one week after undergoing stent implantation had much higher levels of soluble Fas ligand and significantly lower levels of soluble Fas than patients without coronary intervention. Serum levels of soluble Fas ligand and NMP in patients with coronary restenosis were significantly higher than those in patients without restenosis. Serum levels of soluble Fas and soluble Fas ligand in patients one week after undergoing stent implantation who had coronary restenosis were markedly lower and higher than in patients without restenosis, respectively. Serum levels of soluble Fas ligand were positively correlated with NMP in those patients. These results indicate that coronary restenosis might be affected by the Fas/Fas ligand system. We conclude that measurement of soluble Fas, soluble Fas ligand and NMP is useful for determination of coronary restenosis in patients with ischemic heart disease.

Angioplasty, Balloon, Coronary↗

PubMed1981

Effect of macromolecules on aqueous solubility of cholesterol and hormone drugs.

The solubility of cholesterol and some hormone drugs in aqueous macromolecule solutions was investigated. Polyvinylpyrrolidone, dextrans, and heparin increased the solubilities of progesterone, testosterone, and diethylstilbestrol, while acacia, pectin, and carrageenans decreased their solubilities. Dextrans increased the solubilities of cholesterol and the three hormone drugs. Acacia and pectin greatly increased cholesterol solubility; however, these macromolecules significantly decreased progesterone and diethylstilbestrol solubilities and slightly decreased progesterone solubility. Heparin decreased cholesterol solubility and increased progesterone, testosterone, and diethylstilbestrol solubilities. Carrageenans significantly decreased cholesterol, progesterone, and testosterones solubilities and had little effect on diethylstilbestrol solubility. A strong bathochromic shift in the absorption spectra of progesterone and testosterone in polyvinylpyrrolidone solutions indicated an attachment between the polymer and the C=O group of the steroids.

Cholesterol↗

PubMed1981

Extended Hansen solubility approach: naphthalene in individual solvents.

A multiple regression method using Hansen partial solubility parameters, delta D, delta p, and delta H, was used to reproduce the solubilities of naphthalene in pure polar and nonpolar solvents and to predict its solubility in untested solvents. The method, called the extended Hansen approach, was compared with the extended Hildebrand solubility approach and the universal-functional-group-activity-coefficient (UNIFAC) method. The Hildebrand regular solution theory was also used to calculate naphthalene solubility. Naphthalene, an aromatic molecule having no side chains or functional groups, is "well-behaved', i.e., its solubility in active solvents known to interact with drug molecules is fairly regular. Because of its simplicity, naphthalene is a suitable solute with which to initiate the difficult study of solubility phenomena. The three methods tested (Hildebrand regular solution theory was introduced only for comparison of solubilities in regular solution) yielded similar results, reproducing naphthalene solubilities within approximately 30% of literature values. In some cases, however, the error was considerably greater. The UNIFAC calculation is superior in that it requires only the solute's heat of fusion, the melting point, and a knowledge of chemical structures of solute and solvent. The extended Hansen and extended Hildebrand methods need experimental solubility data on which to carry out regression analysis. The extended Hansen approach was the method of second choice because of its adaptability to solutes and solvents from various classes. Sample calculations are included to illustrate methods of predicting solubilities in untested solvents at various temperatures. The UNIFAC method was successful in this regard.

Chemical Phenomena↗

PubMed1989

Effect of temperature and fat content on the solubility of hydrochlorothiazide and chlorothiazide in milk.

The solubility of hydrochlorothiazide and chlorothiazide in milk has been studied. Experiments were carried out at 5, 15, 25, and 37 degrees C on a buffer solution of pH 6.5, a 2.6% solution of casein, bovine skim milk samples, and bovine milk samples with fat contents of 0.75, 1.70, and 3.50%. The "total" solubility of both drugs in the media studied was higher than the buffer solubility. The highest "total" solubility for both drugs was observed in skim milk. Based on binding data of thiazides to milk, the "total" solubility was split into "free" and "bound" solubility. The increases of solubility noted cannot be explained on the basis of drug-milk binding data. The enhancement of solubility was attributed to the increase of intrinsic solubility of drugs in milk. Results of the thermodynamic analysis of solubility data showed that a different solubilization process of hydrochlorothiazide may be responsible for the high solubility values found in skim milk for this drug. In contrast, the thermodynamic parameters of chlorothiazide in all types of milk are similar, indicating a common solubilization mechanism. The biopharmaceutical significance of the findings is discussed in light of the freeze-dried drug-milk formulations and coadministration of drugs with milk in general.

Animals↗

PubMed1993

Solubility of nickel oxide particles in various solutions and rat alveolar macrophages.

The solubility of five types of commercial nickel oxide particles was determined in different types of solutions, including distilled water, physiological saline, buffered saline, and tissue-culture medium, in order to estimate their solubility in the human respiratory tract. In addition, we examined the solubility of the two types of particles that were the most and least soluble particles of the above five types of nickel oxide, in rat alveolar macrophages cultured in vitro. The solubility of the nickel oxide particles in these solutions varied remarkably with their types, suggesting that, even though they are called as "nickel oxide," their solubilities are different among the manufacturer and the product lot. Their solubilities were also influenced by the types of solution and the existence of carbon dioxide in the atmosphere. The solubility of nickel oxide particles in the alveolar macrophages was significantly larger than that observed in the culture medium without macrophages, but smaller than that observed in the distilled water. These results suggest that the actual solubility of nickel oxide particles in the respiratory tract may be difficult to estimate by the conventional solubility analysis method using distilled water, and that the enhancement of particle dissolution by the alveolar macrophages and the depression of particle solubility by the coexisting salt and carbon dioxide should be taken into consideration for the accurate estimation.

Animals↗

PubMed2001

Soluble ICAM-1 and E-selectin levels correlate with clinical and biological aspects of severe ovarian hyperstimulation syndrome.

OBJECTIVE: To assess the potential involvement of the soluble endothelial cell-leukocyte adhesion molecules E-selectin and intercellular adhesion molecule-1 (ICAM-1) in the pathophysiology of capillary hyperpermeability in the ovarian hyperstimulation syndrome (OHSS). DESIGN: Controlled clinical study. SETTING: Women hospitalized for severe OHSS after ovulation induction for IVF at two tertiary medical centers. PATIENT(S): Eleven patients with severe OHSS undergoing IVF and 20 controls who had received a similar ovulation induction regimen and did not develop OHSS. INTERVENTION(S): Serial serum samples were obtained from all patients with OHSS from admission until discharge. Ascitic fluid was obtained from all patients by therapeutic paracentesis. Serum was obtained from all controls 4-8 days after ET. MAIN OUTCOME MEASURE(S): Samples were assayed for soluble E-selectin and soluble ICAM-1 by using enzyme-linked immunosorbent assay and results were correlated with clinical and biological aspects of OHSS. RESULT(S): Compared with controls, patients with severe OHSS had higher levels of soluble ICAM-1 and lower levels of soluble E-selectin detected in serum and ascites. Serum levels of soluble ICAM-1 decreased, while soluble E-selectin levels increased along with clinical and biological improvement. Serum soluble ICAM-1 showed significant positive correlation and serum soluble E-selectin showed significant negative correlation with clinical and biological aspects of severe OHSS. CONCLUSION(S): Soluble ICAM-1 and soluble E-selectin seem to be involved in the pathophysiology of capillary hyperpermeability in severe OHSS.

Adult↗

PubMed1983

Assessment of cystine solubility in urine and of heterogeneous nucleation.

Factors affecting cystine solubility were sought in an effort to derive a reliable method for estimating urinary saturation with respect to cystine. In synthetic solutions, cystine solubility was measured from the maximum ambient cystine concentration reached after incubation with an excess of solid cystine. It rose progressively as the ionic strength increased from addition of mineral electrolytes. The increment in cystine solubility between ionic strength of 0.005 and 0.3 ranged from 13 mg./1. for potassium chloride to 70 mg./1. for calcium chloride. Urinary macromolecules (less than 5,000 daltons, obtained by ultrafiltration), at concentrations normally expected to be found in urine, increased cystine solubility by as much as 45 mg./1. Because of these actions of electrolytes and macromolecules, cystine solubility in urine (from control subjects and patients with cystinuria) exceeded solubility in synthetic solution containing 5 mM sodium cacodylate by 68 to 89 mg./1. Thus, the saturation of cystine in individual urine samples cannot be estimated by comparing the original cystine concentration with a defined cystine solubility curve. It may be more accurately measured as the ratio of original cystine concentration and the directly determined cystine solubility in urine. The estimated assessment of urinary saturation with respect to cystine was shown to deviate from the empirically derived measure from -33 to +44 per cent. In conclusion, cystine is more soluble in urine because of the effects of electrolytes and macromolecules. Thus, urinary saturation of cystine cannot be estimated from solubility curves but must be empirically derived from the direct assessment of cystine solubility in individual urine samples.

Calcium Oxalate↗

PubMed1997

Serum soluble human leucocyte antigen class I in paediatric liver transplantation with live, related donors.

Serum soluble human leucocyte antigen (HLA) class-I is a useful marker for predicting immunological events in organ transplantation. In cadaver liver transplant cases it is especially the case that high amounts of soluble HLA-I are excreted from the grafts. In Japan, almost all liver transplants have been performed from living parent donors to their children. Therefore, it is interesting to know how soluble HLA-I changes in relation to clinical course. As part of this study we first examined serum concentrations of soluble HLA-I in 33 paediatric patients using enzyme-linked immunosorbent assay. Soluble HLA-I is composed of three different sized molecules (45, 39 and 34-36 kDa); then the change of distribution of these three molecules was demonstrated by Western blot analysis. When donor and recipient have different soluble HLA-I band patterns, the origin of the antigen can be assumed by this method. We found that in a comparison between pre- and post-transplants, the six out of eight (75%) patients that suffered episodes of acute rejection showed a significant elevation of soluble HLA-I, and all patients with infectious episodes had an elevated soluble HLA-I. Meanwhile, 10 out of 22 (45%) patients without any clinical complications still showed increased soluble HLA-I. The Western blot analysis showed that the soluble HLA-I molecules were considerably derived from the grafted liver, from one week to 24 months after grafting. In acute rejection, the band signals of donor origin were significantly increased. These signals were attenuated after immunosuppressive therapy. The grafted liver appears to contribute to the increase of soluble HLA-I following liver transplantation, and this increase is greater with the effects of the host immune system.

Adolescent↗

PubMed1996

Solubility behavior, phase transition, and structure-based nucleation inhibition of etanidazole in aqueous solutions.

PURPOSE: The solubility behavior, phase transition and inhibition of the nucleation process of etanidazole were characterized. METHODS: Solubility measurements as a function of time permitted characterization of the solubility behavior and phase transition. The precipitate from saturated solutions was isolated and characterized by differential scanning calorimetry, polarized light microscopy, x-ray powder diffraction and coulometric analysis. The physical stability of metastable systems was examined in the presence of various structure-based nucleation inhibitors. RESULTS: Etanidazole is soluble in water with an equilibrium solubility of 68.1 mg/mL, pH 6.5 with changes in pH having virtually no effect on the solubility. Etanidazole reaches concentrations in excess of 150 mg/mL within one hour. Etanidazole solutions prepared at 150 mg/ mL contained crystals after rotating for 24 hours. The crystals were isolated and characterized as etanidazole monohydrate. the solubility of etanidazole monohydrate in water increased with time reaching an equilibrium solubility of 68 mg/mL after 24 hours. Therefore, the solubility studies were actually determining the solubility of the more stable monohydrate from of etanidazole. Etanidazole solutions at concentrations of 50, 100 and 150 mg/mL were stabilized to varying degrees with structure-based nucleation inhibitors (imidazole, ethanolamine or diethanolamine). CONCLUSIONS: Anhydrous etanidazole undergoes a transition in aqueous solutions to the more stable monohydrate when the solubility of the monohydrate is exceeded. The physical stability of etanidazole solutions at 4 degrees C is improved following autoclaving. The addition of structure-based nucleation inhibitors effectively stabilized the metastable systems.

Calorimetry, Differential Scanning↗

PubMed2004

Miniature device for aqueous and non-aqueous solubility measurements during drug discovery.

PURPOSE: A miniature device was developed for the measurement of aqueous and non-aqueous equilibrium solubility during drug discovery. The solubility values obtained using the miniature device were compared to those obtained using the conventional shake-flask method. METHODS: The aqueous solubility of six structurally diverse compounds, the solubility of carbamazepine in various cosolvent systems, and the pH-solubility profile of saquinavir were determined using the miniature device. The device contains a multichannel cartridge pump and a Tygon tubing that is mounted on the pump with two ends linked by a syringe filter. The drug slurry was filled into the tubing and circulated inside, continually passing through the syringe filter. At the end of the experiment, the filtrate was collected and analyzed directly by High-Pressure Liquid Chromatography (HPLC). The solubility was also determined by the shake-flask method. RESULTS: The solubility values determined by the miniature device were in good agreement with those measured by the conventional shake-flask method. CONCLUSIONS: The miniature device provides a unique way of testing aqueous and non-aqueous equilibrium solubility in a microscale setting. With approximately 1 mg of compound, it is possible to determine the entire pH-solubility profile. The device is useful for solubility screening during lead optimization and candidate selection in early drug discovery, when compound supply is limited. It can also be used for screening solubility in non-aqueous systems to select vehicles for preclinical in vivo studies.

Anti-HIV Agents↗