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A marked elevation in plasma triglycerides is observed when experimental animals are anesthetized with a pentobarbital sodium injection (Nembutal), a most widely used anesthetic in animal experiments. This is proven, however, to be a false rise due to the interference of propylene glycol present in the solvent of the injection with the plasma triglyceride determinations. One mole of propylene glycol produces one mole of formaldehyde by oxidation. The formaldehyde thus generated from propylene glycol mixes with those from glycerol moiety of plasma triglycerides, and gives an enhanced color reaction to all chromogenic reactions with formaldehyde. Since most of the chemical methods for plasma triglyceride determination is based on either one of these color reactions, we have to pay attention to a hypertriglyceridemia due to such influence as exerted by a solvent additive of propylene glycol upon the triglyceride measurements.
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PMID:Interference of an anesthetic preparation with plasma triglyceride determinations. 56 75

The degradation kinetics of pentobarbital sodium in propylene glycol-based solutions were studied along with the in vivo effects in laboratory animals. The degradation rate constant was directly proportional to the water concentration in propylene glycol-water solvent systems. An activation energy of 23.4 kcal/mole was obtained in propylene glycol-water (1:1). Pentobarbital sodium solutions in anhydrous propylene glycol and 9:1 mixtures of propylene glycol with ethanol, glycerin, or dimethylacetamide gave relatively slow degradation rates at 100 degrees with all projected 25 degrees t 99% values greater than 4.5 years. Intravenous administration of pentobarbital sodium in various anhydrous propylene glycol-based vehicles to rats produced no hemolysis of gross organ damage that would interfere with pathological evaluations. Results of an intraperitoneal sleeptime study indicated that pentobarbital sodium produced consistent hypnotic effect when administered as an aqueous solution or in anhydrous propylene glycol-based vehicles.
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PMID:Stable nonaqueous pentobarbital sodium solutions for use in laboratory animals. 87 53

The solubilities of the methyl, ethyl, propyl, and butyl esters of p-hydroxy- and p-aminobenzoates have been determined in propylene glycol:water mixtures. The log of the observed solubility data in propylene glycol:water mixtures was examined for deviations from the following equation: In Xi = f In (Xc) + (1 - f) In (Xw), where Xi is the calculated mole fractional solubility of the solute, f is the volume fraction of cosolvent, Xc is the observed mole fractional solubility in the neat cosolvent, and Xw is the solubility in water. In each case, the deviations from the predicted solubilities demonstrated a characteristic pattern. Positive deviations were observed at high volume fractions of cosolvent, while negative deviations were observed at low volume fractions. The magnitude of the deviations at low volume fractions of cosolvent was related to the carbon chain length within each group of esters. A similar phenomenon was not observed at high volume fractions of cosolvent; however, the magnitude of the deviations was dependent on the nature of the polar group on the ester. The data are interpreted in terms of the possible effects of solvent structure on the solubility of the solutes.
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PMID:Influence of solute structure on deviations from the log-linear solubility equation in propylene glycol:water mixtures. 188 Jul 29

The complex formation of a series of aromatic compounds with povidone was studied in buffer solutions and organic solvent mixtures by equilibrium dialysis. For all the ligand molecules studied, a linear relationship was found between r, the number of moles of bound ligand per mole of povidone, and the free ligand concentration. The binding constants and the free energies of binding (-delta F), were greater for compounds in the nonionic state and increased with the number of hydroxyl groups which were capable of forming hydrogen bonds. They decreased with temperature elevation. The thermodynamic data showed entropy gains during the binding process accompanied by small negative enthalpy values. The increased ability to form hydrogen bonds and the increase in ionization of the ligand molecule was reflected in more negative delta H and decreasing delta S values. (The thermodynamic values were interpreted on the basis of the "iceberg" concept of water structure.) From these entropy and enthalpy changes, hydrogen and hydrophobic bondings appeared to be the most important types of binding. In organic solvent mixtures, the association constants lowered with increasing ethanol or propylene glycol concentration; a line relationship between the free energy and the dielectric constant of the solvent mixtures was observed.
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PMID:Interaction of povidone with aromatic compounds III: Thermodynamics of the binding equilibria and interaction forces in buffer solutions at varying pH values and varying dielectric constant. 709 3

The solubility profiles of theobromine, theophylline, and caffeine at 25 degrees were examined in binary solvent systems including dioxane-formamide, water-polyethylene glycol 400, and glycerin-propylene glycol. Theobromine solubility was studied in dioxane-water mixtures, a solvent system that was investigated earlier for the solubility of theophylline and caffeine. Solubilities were calculated in these polar systems by a regression method, based on an extension of the Hildebrand-Scatchard equation of regular solution theory. A linear relationship between the mixed solvent solubility parameter, and dielectric constant, epsilon, was introduced earlier and was confirmed in the present study. In addition, it was observed that a regression of log (activity coefficient) on epsilon in a second or higher degree polynomial provides reasonable solubility values for the methylxanthines in mixed solvents. A direct regression of molal or mole fraction (but not molar) solubility against delta 1, epsilon, or against volume percent of one or the other solvent in a binary solvent mixture provided a suitable measure of solubility for these crystalline drugs in mixed polar solvents. The drug's solubility parameter as determined from peak solubility in mixed polar solvents varied somewhat, depending on the specific solvent system employed. It is suggested that a drug may exhibit one (or more) solubility parameters in nonpolar solutions and multiple solubility parameters in polar systems. The extended solubility approach serves for the back-calculation of solubilities in mixed solvent systems, even though the solubility parameter of the solute may vary from one solvent system to the next.
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PMID:Extended Hildebrand Solubility Approach: methylxanthines in mixed solvents. 729 44

The degradation kinetics of neostigmine were studied in aqueous solutions with varied pH from 1.5 to 9.9 under accelerated storage conditions. The stability of neostigmine in solutions containing propylene glycol or polyethylene glycol 400 was also investigated. The reaction order of neostigmine in these aqueous and solvent systems followed pseudo-first-order degradation kinetics. The degradation rates of neostigmine under various buffer concentrations within the investigated pH range were obtained. They indicated that the degradation was independent of the species of buffering agent. Maximum stability of neostigmine was determined at pH 5.0 buffer species conditions. The activation energy could be estimated from the Arrhenius plot as 15.72 kcal/mole. The half-life of 883.7 days was estimated at room temperature in 0.1 M, pH 4.9 acetate buffer solution (mu = 0.5). Ultraviolet (UV) irradiation at 254 nm of the neostigmine solutions in pH 4.9 acetate buffer showed an accelerated degradation in comparison with light-protected samples. Incorporation of propylene glycol into the neostigmine solution at pH 4.9 enhanced the stability; however, an adverse effect on the stability of neostigmine was noted when a polyethylene glycol 400 solvent system was used.
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PMID:Degradation kinetics of neostigmine in solution. 1106 98

The mole fraction solubility of a poorly water soluble loop diuretic, furosemide, was determined in aqueous binary mixtures of ethanol, propylene glycol, and glycerol from 0% to 100% cosolvent concentrations at 25 degrees C. Solubility predictions based on the minimum number of experimental data points were performed using the commonly used accurate cosolvency models: the three-suffix excess free energy (3xEFE), the mixture response surface (MRS), the combined nearly ideal binary solvent/Redlich-Kister (CNIBS/R-K), and the general single model (GSM). This prediction method was tested using three sets of solubility data for furosemide generated in this study and 11 data sets collected from the literature. The average percentage deviations (APDs) were 8.4 +/- 3.8, 13.6 +/- 7.3, 7.4 +/- 2.8, and 7.6 +/- 2.9, respectively, for 3xEFE, MRS, CNIBS/R-K, and GSM models. Using 3xEFE, CNIBS/R-K, and GSM models, which are theoretically related, a mean predicted solubility (MPS) approach was also proposed. The APD for this method was 7.3 +/- 2.3. The mean differences between MRS and the others were statistically significant (p < .001). The results showed that one can employ solubility prediction based on a minimum of five experimental data points, and the expected APD is less than 10%.
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PMID:Solubility prediction for furosemide in water-cosolvent mixtures using the minimum number of experiments. 1154 65

The solubility of four benzodiazepines (BZPs) including diazepam (DIZ), lorazepam (LRZ) clonazepam (CLZ), and chlordiazepoxide (CHZ) in water-cosolvent (ethanol propylene glycol and polyethylene glycol 200) binary systems were studied. In general, increasing the volume fraction of cosolvents resulted in an increase in the solubility of benzodiazepines. The mole fraction solubilities were fitted to the various cosolvency models, namely extended Hildebrand approach (EHA), excess free energy (EFE), combined nearly ideal binary solvent/Redlich-Kister (CNIBS/R-K), general single model (GSM), mixture response surface (MR-S). double log-log (DL-L), and linear double log-log (LDL-L). The results showed that DL-L model was the best model in predicting the solubility of all drugs in all the water-cosolvent mixtures (OAE% = 4.71). The minimum and maximum errors were observed for benzodiazepine's solubility in water-propylene glycol and water-ethanol mixtures which were 2.67 and 11.78%, respectively. Three models (EFE, CNIBS/R-K and LDL-L) were chosen as general models for solubility descriptions of these structurally similar drugs in each of the solvent systems. Among these models, the EFE model was the best in predicting the solubility of benzodiazepines in binary solvent mixtures (OAE% = 11.19).
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PMID:Prediction of benzodiazepines solubility using different cosolvency models. 1216 13

Alkyl esters of ketorolac were synthesized as potential prodrugs for transdermal delivery and evaluated to determine the relationship between their skin permeation characteristics and their physicochemical properties. Solubility of the prodrugs in various vehicles was determined at room temperature while lipophilicity was obtained as 1-octanol/water partition coefficients (logP) and capacity factors (k') using HPLC. Metabolism of the prodrugs to ketorolac was studied both in rat skin homogenate and in plasma. Rat skin permeation characteristics of the prodrugs saturated in propylene glycol were investigated using the Keshary-Chien permeation system at 37 degrees C. An increase in logP and capacity factor values of the prodrugs were observed in proportion to their alkyl chain length. Good linear relationship between the logP values and capacity factor was observed (r(2) = 0.92). Prodrugs were rapidly degraded to ketorolac both in the skin homogenate and in plasma following a first-order kinetics. To determine accurate amounts of prodrug permeated, both the prodrug and parent drug concentration in the receptor solution were determined in mole units. The skin permeation rate of the alkyl ester prodrugs was significantly higher with a shorter lag time than that of ketorolac. The permeation rate of ketorolac reached maximum in its 1-propyl ester form as 46.61 nmol/cm(2)/h, and a parabolic relationship was observed between the permeation rate and the logP values of the prodrugs. Alkyl ester prodrugs of ketorolac having optimum lipophilicity could improve the transdermal delivery of ketorolac.
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PMID:Synthesis and evaluation of Ketorolac ester prodrugs for transdermal delivery. 1271 20

A transdermal patch for delivering nicotine for periods of 12-48h was designed. An inclusion complex formed between the nicotine and beta-cyclodextrine (beta-CD) was used in drug depot. The usefulness of a specially cross-linked polyvinyl alcohol (cross-PVA) membrane was investigated as a rate controlling membrane. The influence of carbopol polymers, type C-934P and C-940 and propylene glycol on transdermal permeation of nicotine through the rat skin was investigated. The results indicated a maximum flux of 42 microgcm(-2)h(-1) after 48 h from the patches made from C-934P when the propylene glycol concentration was 15% and the nicotine-beta-CD mole ratio in the inclusion complex was 3:1. These nicotine transdermal patches can be fabricated to obtain a controlled release, zero order systems.
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PMID:Development of a novel prolonged-release nicotine transdermal patch. 1566 73


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