INTERACTION OF SOME PHARMACEUTICALS WITH MACROMOLECULES. I. EFFECT OF TEMPERATURE ON THE BINDING OF PARABENS AND PHENOLS BY POLYSORBATE 80 AND POLYETHYLENE GLYCOL 4000

Preventing False Negatives for Histochemical Detection of Phenolics and Lignins in PEG-Embedded Plant Tissues

Polyethylene glycol (PEG) is a low-cost and advantageous embedding medium, which maintains the majority of cell contents unaltered during the embedding process. Some hard or complex plant materials are better embedded in PEG than in other usual embedding media. However, the histochemical tests for phenolics and lignins in PEG-embedded plant tissues commonly result in false negatives. We hypothesize that these false negatives should be prevented by the use of distinct fixatives, which should avoid the bonds between PEG and phenols. Novel protocols for phenolics and flavanols detection are efficiently tested, with fixation of the samples in ferrous sulfate and formalin or in caffeine and sodium benzoate, respectively. The differentiation of lignin types is possible in safranin-stained sections observed under fluorescence. The Maule's test faultlessly distinguishes syringyl-rich from guaiacyl- and hydroxyphenyl-rich lignins in PEG-embedded material under light microscopy. Current hypothesis is corroborated, that is, the adequate fixation solves the false-negative results, and the new proposed protocols fill up some gaps on the detection of phenolics and lignins.

Efficiency of the Polyethylene-Glycol (PEG) Embedding Medium for Plant Histochemistry

Histochemical analyses in plants are commonly performed on hand-made sections of fresh materials. The disadvantages of embedding in historesin, paraffin or paraplast® are the alterations to cellular contents, the high costs and few evident results, depending on the test. Polyethylene-glycol (PEG), as a low cost, hydrophilic medium that maintains most of the cellular features similar to fresh conditions, may be useful for obtaining good histochemical results in thinner and homogeneous sections. The current study aimed to compare the efficiency of PEG as an embedding medium for histochemical analyses of primary and secondary metabolites accumulation. Using hand-made sections of fresh samples (T1) as a comparison, we tested the influence of the use of Karnovsky's solution as a fixative (T2) versus embedding in PEG (T3). The samples herein analyzed comprise leaves, stems, seeds and insect galls of different plant species. Neither the Karnovsky's fixative nor the embedding in PEG altered the histochemical results for starch, lipids, terpenoids, proteins and reducing sugars in T1, T2, and T3. However, PEG binds to phenols, such as tannins, flavonoids and lignins, thereby presenting false negatives in T3.

The influence of diphenhydramine on the absorption of methaqualone in man

1 The effects of diphenhydramine on the buccal absorption, in vivo absorption and the in vitro dissolution of methaqualone have been studied. 2 Diphenhydramine significantly reduced the buccal absorption of methaqualone and the effect was dose and pH dependent. In vivo, diphenhydramine did not alter the rate of absorption or the distribution of methaqualone in blood. In vitro, the presence of diphenhydramine increased the rate of dissolution of methaqualone and the effect was more marked when the particle size was small. 3 The reasons for and the implications of these apparently contradictory results are discussed and it is concluded that any increased efficacy resulting from combining diphenhydramine with methaqualone cannot be due to increased plasma drug levels.

Micellization and solubilization behavior of sucrose laurate, a new pharmaceutical excipient

The micellization and solubilization properties of sucrose laurate have been investigated. Solubilization experiments showed that numerous poorly water-soluble drug substances could be solubilized by aqueous sucrose laurate solutions; the solubilization was uncomplicated and the maximum solubilizate concentration was high. Laser light scattering investigations proved that solutions containing pure sucrose monolaurate formed spheroidally shaped micelles with a hydrodynamic radius of 29.2 A, which behaved like ideal particles, showing no solute-solute interactions. Surprisingly, the hydrodynamic radii of the sucrose monolaurate micelles were hardly changed by the introduction of 0.20% cyclosporin-A. The addition of sucrose dilaurate, the main impurity of the sucrose laurate product, however, resulted in large and polydisperse structures. Considering the critical packing parameters, the light scattering results could be explained by assuming a transformation of the spherical micelle into a disk with rounded edge.

Effect of some syrup constituents on the solubility of sorbic acid

The effects of sucrose, glucose, sorbitol, and saccharin on the aqueous solubility of sorbic acid at 20 and 37 degrees C were determined. Sucrose, glucose, and sorbitol decreased the solubility of sorbic acid with increasing concentrations at both temperatures. Increasing the concentrations of these sweetening agents resulted in decreases in the dielectric constants. Calculation of the free energy and enthalpy changes indicated that the dissolution process for sorbic acid became progressively unfavorable with increasing sugar concentration.

Interaction of povidone with aromatic compounds V: Relationship of binding tendency in a macromolecular solution treated as a pseudo two phase and a monophase

The pseudo-two-phase model is proposed to correlate complex formation of ligand molecules with povidone with partition coefficients (log P or II constants). The conditions which permit the use of the pseudo-two-phase model for binding of ligand onto macromolecules are determined. This model seems to be a more rational choice than the frequently used complex formation model (monophase). This is demonstrated theoretically and confirmed experimentally. The advantages of the use of such a model are also discussed.

Interaction of povidone with aromatic compounds IV: effects of macromolecule molecular weight, solvent dielectric constant, and ligand solubility on complex formation

Complex formation of ligand molecules with povidone was investigated to elucidate the effect of the molecular weights of the macromolecule and the influence of the solvent dielectric constant on the complexing tendency. The higher molecular weight polymers were more effective complexing agents than those with lower degrees of polymerization. When studying complex formation as a function of the dielectric constant (D), a linear relationship was noted between D and log B/F (B/F representing the ratio of bound to free ligand); the use of solvent mixtures to achieve a range of solvent dielectric constants enabled changes of the pH of the solvent, ligand dissociation, and solubility of the ligand and macromolecule. Of the variables under investigation, only the change in ligand solubility seemed to play an important role: a linear relationship was noted between the complexing tendency (log B/F) and the logarithm of the inverse of the ligand molecule solubility in the solvent mixtures (log 1/S). It was concluded that the change in solubility of the ligand was the predominant factor in the decrease of the complexing tendency with decreasing dielectric constant.

Protein binding of anthraquinone glycosides, with special reference to adriamycin

The binding of anthraquinone glycosides (adriamycin, adriamycinol, daunorubicin, daunorubicinol, and 4'epiadriamycin) to human serum albumin and human plasma has been studied by equilibrium dialysis. About 62% of adriamycin was bound to human serum albumin (45 g/l). Only minor variations in the degree of binding were observed between the anthraquinone glycosides. The binding degree of adriamycin in plasma from cancer patients was not significantly different from that observed in healthy volunteers, the fraction of free adriamycin being 24.56% +/- 4.51%, and 27.67% +/- 2.78%, respectively. The plasma albumin concentration was significantly lower in cancer patients than in the healthy volunteers (26.90% +/- 5.88% and 39.24% +/- 1.74%, respectively). In cancer patients the fraction of free adriamycin decreased with increasing plasma albumin concentration.

Interaction of povidone with aromatic compounds I: Evaluation of complex formation by factorial analysis

In a study of complex formation between macromolecules and small ligands such as drugs, it appeared that the association constants must be calculated with more care (i.e., after a thorough investigation of the influencing parameters such as buffer composition, ionic strength, and temperature) to allow meaningful interpretations of the phenomena. For this purpose, factorial analysis seems to be the method of choice; it offers the advantage of evaluating the influence of several variables and their interactions at the same time with a minimum of experiments. The method was applied to the association of povidone with two ligands, salicylic acid and benzoic acid. Parameters such as buffer composition and ionic strength, which affect binding, could be distinguished. Especially at pH 7.00, a great positive influence of buffer ions (phosphate buffer) and a relative positive interaction between temperature and ionic strength were noted. Knowledge of the influences of these parameters allowed comparison of the effects of the functional groups attached to the ligand molecules, as well as their degree of dissociation, on adsorption to permit more meaningful interpretation of thermodynamic constants.

Effect of polyols on interaction of paraben preservatives with polysorbate 80

A quantitative study of the interaction of the methyl, ethyl, propyl, and butyl esters of p-hydroxybenzoic acid with polysorbate 80 in the presence and absence of two polyols (propylene glycol and glycerol), which were potential competitors, was performed. The results indicate that neither competitor displaced significant amounts of the parabens from their binding sites on polysorbate 80. The previously observed synergistic antimicrobial effects of these polyols appear to be due to a mechanism other than the displacement of the parabens from their micellar binding sites.

Benzocaine diffusion from polyethylene glycol through human stratum corneum

The diffusion, penetration, and surface effects of benzocaine incorporated in various polyethylene glycol ointment bases through human stratum corneum were studied. Benzocaine diffusion was measured by following the benzocaine concentration in the receiving compartment of a diffusion cell. The ointment was placed in the other cell compartment and was separated from the receiving compartment by sheets of human stratum corneum. Surface effects were monitored by scanning electron micrographs of the stratum corneum. Results showed a decrease in drug diffusion in the presence of relatively high amounts of the lower molecular weight portions of polyethylene glycol. Scanning electron microscope studies showed that both benzocaine and polyethylene glycol affect the surface structure of the stratum corneum. Thermal analysis indicated that benzocaine dissolves in polyethylene glycol.

Effect of sorbitol on interaction of phenolic preservatives with polysorbate 80

The effect of sorbital on the binding of several commonly used phenolic preservatives (i.e., p-hydroxybenzoic acid, methylparaben, ethylparaben, and propylparaben) with the nonionic surfactant polysorbate 80 was investigated using an equilibrium dialysis technique. The binding data were expressed in the form of Scatchard plots utilizing a modified form of the Scatchard equation. The data analysis indicated that all four phenolic preservatives were bound to two distinct loci within the polysorbate micelle; one exhibited a high affinity and a low capacity for the preservative molecules, while the other appeared to have a near-zero affinity but an almost infinite binding capacity. The high affinity site was assumed to be located near the junction of the hydrocarbon core with the polyoxyethylene region of the micelle. The interaction of the preservatives with the second class of sites apparently involved a non-specific and nonsaturable partitioning of the preservative molecules into the polyoxyethylene region of the micelle. Sorbitol was ineffective in displacing significant amounts of bound preservative from either binding site, presumably because it was too polar to partition into the micelle sufficiently to displace bound preservative.

Effect of a second solubilizate on the partition coefficient of drugs in micellar solution and their permeation rate across an artificial membrane

The distribution of a solubilizate between micelles and the aqueous phase does not obey a simple partition law when a second solubilizate species is present. Alterations of the apparent partition coefficient cannot be explained in terms of a simple displacement mechanism, following the interaction of both solubilizates with the same site of the micelle. A non linear increase in solubilizate association to micelles following an increase in surfactant concentration is observed in the presence of a second solubilizate. A depression in the cloud point temperature follows the addition of a second species and is such that cannot be interpreted as a simple additive effect. Alteration of the apparent partition coefficient in a miscellar solution has an effect on the permeation rate of the solubilizate across an artificial membrane. Biopharmaceutical implications are discussed.

Solubilization of hydrocortisone, dexamethasone, testosterone and progesterone by long-chain polyoxyethylene surfactants

Solubility and dialysis methods were used to study the solubilization of hydrocortisone, dexamethasone, testosterone and progesterone in aqueous long-chain polyoxyethylene non-ionic surfactant solutions. Partition coefficients, Km, between micellar and aqueous phases were calculated between 10-50 degrees. Km decreased with temperature and polyoxyethylene chain length but increased with decrease in steroid polarity. The standard free energy change, deltaGOS, for the solubilization of the steroids decreased with decrease in steroid polarity and surfactant hydrophilic chain length but was essentially independent of temperature. The enthalpies and entropies for the process were determined from the variation of Km with temperature. deltaHOS and deltaSOS increased with decreasing steroid polarity but were essentially independent of temperature and polyoxyethylene chain length.

The effect of ageing on plasma pethidine concentration

1. Plasma pethidine levels have been monitored after the administration of 1.5 mg/kg intramuscularly to a group of young (under 30) and old (over 70) subjects. 2. Plasma levels were consistently higher in the old group, this was most marked for the first three hours but for most of the study there was a more than two-fold difference. 3. Differences in uptake from muscle and in metabolism were small and appeared unimportant. 4. Less pethidine was excreted in the elderly and this contributed to the overall differences in serum levels but was not important in explaining the marked disparity noted over the first three hours. 5. Red cell binding of pethidine by the young was much greater than by the old and if the differences in drug binding also applies to other tissues this would explain the high serum levels in the old and the increased incidence of side effects.

The diffusion of penicillin G and ampicillin through phospholipid sols

The self-diffusion coefficients of penicillin G and ampicillin have been determined at 25 degrees in water and in the presence of a swamping concentration of electrolyte. The antibiotics diffused through phospholipid dispersions at a reduced rate due to interaction with the lipid aggregates. Ampicillin diffused through the phosphatidylcholine and phosphatidylethanolamine dispersions more rapidly than penicillin G, whereas the latter diffused more rapidly through the lysophosphatidylcholine dispersions. Estimates of binding have been made from these data and compared with those obtained from equilibrium dialysis studies. Surface tension measurements indicated that the antibiotics exhibited minimal surface activity. These results have been correlated with data obtained in other studies and a possible explanation has been advanced for the reported differences in vivo activity of penicillin G and ampicillin.

A note on the solubilization of preservative mixtures by cetomacrogol

Preliminary data are reported for the solubilization of several pairs of preservatives by the non-ionic surfactant cetomacrogol. In all cases the addition of a second preservative altered the equilibrium solubility of the first to an extent which depended on the particular co-solute and the concentration added.

Effects of solubilization on drug diffusion

The diffusion of ephedrine, sulphathiazole, chloramphenicol, paracetamol, isoniazid and amphetamine in solutions of Tween 40, Tween 80 and cetomacrogol 1000 have been studied. With the exception of isoniazid, the observed diffusion coefficients, corrected for resistance to flow, depend upon the surfactant used and both the drug and surfactant concentration. The effect of drug solubilization upon the diffusion coefficient is also discussed.

A model for the influence of emulsion formulation on the activity of phenolic preservatives

Basic mathematical models are suggested for calculating the concentration of preservatives which is chemically available in the water of emulsions. It is influenced by the total concentration of preservative in the emulsion, the oil: water partition coefficient of the preservative, the oil: water ratio and the concentration of emulgent. The activity of the preservative is related to the concentration free in the water.

Dissolution rate measurement by an automated dialysis method

An automated dialysis method for measuring the dissolution profiles of unit dose forms is described. The suitability of the method for the evaluation of these profiles has been demonstrated by an examination of tablets of sulphathiazole prepared under different conditions of pressure and excipient content. The addition of the water soluble resin, polyethylene oxide, has been shown to cause a small increase in the dissolution rates of the tablets.

The effects of polyoxyethylene compounds on the hydrolysis of chlorbutol

The rates of hydrolysis of chlorbutol are reduced by surface-active agents, but not by polyethylene glycols. The ratio of the rate-constant in simple aqueous systems to that in systems containing surface-active agents can be predicted if the distribution coefficient for chlorbutol between the micellar pseudo-phase and the aqueous phase is known and is independent of concentration.