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PubMed2002

The effect of surface charge and partition coefficient on the chemical stability of solutes in O/W emulsions.

Methylparaben (MP) was the model solute used to study the effect of surface charge on the rate of degradation in oil-in-water emulsions. The surface charge was varied by adding small amounts of phosphatidylglycerol (anionic) or stearylamine (cationic) to a standard intravenous lipid emulsion stabilized by egg phospholipid. The rates of hydrolysis at pH 8.0 in the water phase, oil phase, interface, and aqueous micellar phase were determined by application of a four-phase kinetic model. The rate of hydrolysis in the aqueous phase was dependent on the zeta potential. This was attributed to the effect of surface charge on the pH of the microenvironment of the oil drops through the phenomena known as surface acidity. MP in the aqueous phase hydrolyzed at a rate associated with the pH of the microenvironment, not the pH of the bulk. The effect of the partition coefficient of the solute was studied by substituting ethylparaben (EP), propylparaben (PP), and butylparaben (BP) for MP in the emulsions used to study the effect of surface charge. The rate of hydrolysis was inversely related to the partition coefficient. The effect of surface charge on the rate of hydrolysis was evident in the emulsions containing MP and EP. Partitioning had the greatest effect on the emulsions containing PP and BP. In general, the effect of surface charge predominated when the partition coefficient was small. The partition coefficient had a greater effect than surface charge when the partition coefficient was large.

Drug Stability↗
PubMed1975

Evaluation of a dynamic permeation technique for studying drug-macromolecule interactions.

The applicability of a permeation rate technique to the determination of drug-macromolecule interactions was tested by measuring the extent of interaction of methylparaben with polyvinylpyrrolidone and polysorbate 80. Results were in agreement with literature data obtained by other techniques. The present method, although restricted to permeant molecules that diffuse readily through nonporous nylon membranes, is of potential value for investigations of drug binding by macromolecules not retained by porous dialysis membranes.

Binding, Competitive↗
PubMed1976

Molecular orbital calculations for parabens: a possible mechanism of action.

Molecular orbital calculations were carried out on the series benzoic acid, p-hydroxybenzoic acid, methylparaben, and ethylparaben. The characteristic trends of this entire series of preservatives are demonstrated by these members. The computer program used was Iterated Extended Hückel Theory. These systems were characterized in terms of atomic charge distributions, effect of hydroxyl and ester groups (both sterically and electronically), preferred molecular conformations, and distinguishing features of molecular orbitals. Through this approach, it was hoped that a common mode of action for all members of this series could be detected and that the trend(s) in this feature would correlate with known trends in activity of members of this series.

Chemical Phenomena↗
PubMed1977

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.

Chemical Phenomena↗
PubMed1978

Simultaneous quantitation of morphine and paraben preservatives in morphine injectables.

A high-performance liquid chromatographic method for the simultaneous determination of morphine sulfate, methylparaben, and propylparaben in morphine sulfate injection was developed. A reversed-phase system, based on an octadecylsilane stationary phase, was used with a binary solvent mobile phase consisting of methanol--phosphate buffer (pH 4.0) containing methanol (5%) delivered at a constant rate (0.6:0.4 ml/min) using a two-pump system. The detector response at 254 nm was linear with the amount injected over a wide range, allowing rapid and reproducible quantitation of each component.

Chromatography, High Pressure Liquid↗
PubMed1979

TLC determination of biotin in a lyophilized multivitamin preparation.

A TLC method for the determination of biotin was developed. The method is selective and sensitive and permits the determination of biotin in the presence of all water-soluble vitamins as well as glycine, edetate sodium, and methylparaben. The main steps are: dissolution of the lyophilized multivitamin preparation in water, addition of the internal standard, application on a thin-layer plate, separation from interfering components, visualization by spraying with 4-dimethylaminocinnamaldehyde, and in situ determination by reflectance measurements. Spraying the plate with paraffin after the coloring procedure increases the sensitivity of the method. The coefficient of variation is 2.3% with 0.15 microgram of biotin/spot. Quantities as low as 10 ng/spot can be determined.

Biotin↗
PubMed1979

High-pressure liquid chromatographic evaluation of aqueous vehicles for preparation of prednisolone and prednisone liquid dosage forms.

A high-pressure liquid chromatographic method was developed that separates prednisolone from prednisone, prednisone from methylprednisolone succinate sodium, and hydrocortisone from hydrocortisone acetate or cortisone acetate. The common liquid dosage preservatives methylparaben, propylparaben, and sodium benzoate do not interfere with quantitative prednisolone, prednisone, and hydrocortisone determinations. The method was used to study prednisolone and prednisone stability in five aqueous vehicles (water, citrate buffer USP, 50% glycerin, 50% sorbitol, and 50% sucrose) containing 10% (v/v) ethanol. Prednisone crystallized out in all vehicles except glycerin, in which it appeared to be stable for at least 92 days. Prednisolone did not crystallize in any vehicle but decomposed quickly in citrate buffer. Sorbitol and glycerin appeared to be the best vehicles for prednisolone. The developed method was applied successfully to the quantitative determinations of prednisolone, prednisone, and hydrocortisone in commercial tablets.

Chromatography, High Pressure Liquid↗
PubMed1979

Solubility in amide-water cosolvent systems II: Cosolvent excess at solute surface.

The solubility of methylparaben was determined at 25 degrees in a series of amide-water cosolvent systems. The data were used to demonstrate the possibility of an amide excess at or near the ester solute over that in the bulk solvent. The analysis, stemming from an interfacial tension-solute area solubility model proposed by earlier workers, involved data obtained as a function of amide concentration and as a function of amide alkylation. Both sets of data support the basic contention of the paper.

Amides↗
PubMed1980

High-performance liquid chromatographic determination of metaraminol bitartrate in the presence of parabens.

A high-performance liquid chromatographic (HPLC) procedure was developed for the determination of metaraminol bitartrate in the presence of methylparaben and propylparaben. Reversed-phase ion-pair chromatography was employed using dioctyl sodium sulfosuccinate as the counterion. The current official USP procedure for the determination of metaraminol requires dilution, extraction, and measurement of UV absorption. The HPLC procedure is rapid and precise and correlates well with the USP XX procedure. It can be used for metaraminol injectables as well as the raw material.

Chromatography, High Pressure Liquid↗
PubMed1981

Rapid and specific high-pressure liquid chromatographic assay for folic acid in multivitamin-mineral pharmaceutical preparations.

A high-pressure liquid chromatographic assay for folic acid in multivitamin-mineral pharmaceutical formulations was developed. The internal standard solution used for sample extraction contained a chelating agent, pentetic acid, for prevention of metal ion-catalyzed degradation of folic acid in th prepared samples. Samples were chromatographed using a paired-ion mobile phase (water-methanol, approximately 76:24; 0.015 M phosphate buffer, pH 7.0; and 0.3% tetrabutylammonium hydroxide) on a column packed with octadecylsilane bonded to microparticulate silica gel. Sample preparation was rapid, and total chromatographic time was approximately 20 min. The method was accurate, precise, and highly specific. Folic acid and the internal standard, methylparaben, were separated from other tablet components and a number of potential impurities and degradation products of folic acid.

Capsules↗
PubMed1983

Determination of antimicrobial preservatives in pharmaceutical formulations using reverse-phase liquid chromatography.

A specific stability-indicating reverse-phase high-performance liquid chromatographic analytical method has been developed to quantitate the antimicrobial preservatives methylparaben, propylparaben, butylparaben, sorbic acid, and benzoic acid in a series of typical pharmaceutical formulations. The mobile phase of this system is a water-acetonitrile mixture, modified by various acids and buffers. The proportions of water and acetonitrile as well as the type and amounts of modifiers are varied in order to achieve optimum chromatography. This method has been used successfully to quantitate preservatives in solutions, suspensions, creams, lotions, and ointments, and can be readily adapted to routine automated assays, either for routine product evaluation or stability programs.

Benzoates↗
PubMed1987

Flocculation of suspensions containing nonionic surfactants by sorbitol.

Aqueous suspensions of sulfamerazine, salicylamide, and butamben, containing either polysorbate 20 or polysorbate 80 as a wetting agent, were deflocculated. The presence of relatively high concentrations of sorbitol in the suspensions resulted in flocculation due to dehydration of surfactant polyoxyethylene groups (reflected by the cloud point). The critical flocculation concentration of sorbitol was reduced by raising the storage temperature, lowering the surfactant concentration, switching from polysorbate 80 to polysorbate 20, or adding sodium sulfate to the suspension formulation. Both the cloud point and the sorbitol critical flocculation concentration depended on the particular drug that was suspended. Methylparaben lowered the cloud point, suggesting that the choice of preservative could influence the suspension characteristics in certain cases. The various dehydrating influences were additive. By assuming that interparticle repulsion becomes negligible at the cloud point, it was possible to use cloud point curves to estimate the critical flocculation concentration of sorbitol.

Benzocaine↗
PubMed1990

A model for alcohol-enhanced permeation through polydimethylsiloxane membranes.

In this study the influence of paraben concentration on flux from solution in 1-propanol through polydimethylsiloxane membranes was investigated. Alcohol was sorbed by the polymer membrane leading to changes in membrane dimensions and increased membrane capacity to contain paraben (partition coefficient). Diffusion coefficients were not significantly influenced by alcohol sorption. Flux was increased 5-30 fold over nonimbibed donors such as water and polyols. An increase in paraben concentration reduced alcohol activity, its uptake by the membrane, and consequently the partition coefficient of paraben. As a result, flux increased with paraben concentration, reached a peak, and then declined. Maximal membrane concentration involves a trade-off between alcohol-membrane interaction (solvent activity) and paraben concentration, and occurred at paraben concentrations in the range of 1.3 to 1.4 mmol/g. At equimolar concentrations, flux was highest for methylparaben and declined as the series was ascended. Differences in flux between parabens at a specified molar concentration were due only to differences in diffusivity.

1-Propanol↗
PubMed1995

Transesterification reactions of parabens (alkyl 4-hydroxybenzoates) with polyols in aqueous solution.

Accelerated stability tests of aqueous solutions containing parabens and polyols were performed using concentrations similar to pharmaceutical and cosmetic formulations. Reaction products were detected in these solutions by HPLC and identified by chromatographic and spectroscopic means. Using xylitol and methylparaben as model reactants, three unknown peaks having the relation 1:2:4 were obtained together with the hydrolysis product 4-hydroxybenzoic acid. Diode array detection gave identical UV spectra for each peak with a maximum at 255 nm. The structures of the isomeric 1-, 2-, and 3-xylityl 4-hydroxybenzoic acid esters were proved by means of LC-MS, GC-MS, and NMR and correlated to the peaks in the HPLC chromatograms. The rate of the transesterification was shown to be highest in strongly alkaline medium (ph 10-11), whereas equilibration of the reaction was optimally balanced at pH 8-9. An increase of polyol concentration enhanced the formation of the esters. The reactivity of different substituted parabens was higher in the case of parabens with a short alkyl ester function. Similar reaction profiles were observed with C3-C6 polyols, but no transesterification took place when aldoses were used.

Chromatography, High Pressure Liquid↗
PubMed2006

Advantages of ultra performance liquid chromatography over high-performance liquid chromatography: comparison of different analytical approaches during analysis of diclofenac gel.

Miniaturization embracing instrumentation, column particle size, and column dimensions is one of the major current trends in separation techniques. This leads to shortening of analysis time and great savings in solvent consumption. Ultra performance liquid chromatography (UPLC) is one of the new developments in liquid chromatography. An ultra-high pressure system allows using of small particle-packed columns with small diameter, which has a positive effect on both system efficiency and analysis time. An analytical method for determination of the active substance diclofenac, the degradation product 1-(2,6-dichlorphenyl)-2-indolinone, and the preservatives methylparaben and propylparaben was used for testing and comparing LC systems. Various octadecylsilica-based analytical columns were examined. Acquity UPLC BEH C18 (2.1 x 50 mm, 1.7 microm) and (2.1 x 100 mm, 1.7 microm) were tested for UPLC. The following analytical columns were used in a test for HPLC: Purospher RP 18e (125 x 4.0 mm, 5 microm), Zorbax Eclipse XDB C18 (75 x 4.6 mm, 3.5 microm), Zorbax Eclipse SB C18 (50 x 4.6 mm, 1.8 microm), as was a monolithic column (Chromolith Performance RP-18e (100 x 4.6 mm). Results of a System Suitability Test (SST) were calculated and compared for each chromatographic peak. System efficiency and analysis duration were compared with regard to solvent consumption and system maintenance

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1996

A novel complex of a phenolic derivative with insulin: structural features related to the T-->R transition.

The structure of a symmetric T3R3f insulin hexamer, complexed with 4-hydroxybenzamide, has been determined using X-ray crystallographic techniques. Data were measured from six crystals grown in microgravity to a resolution of 1.4 A and the structure has been refined including the contributions from hydrogen atoms. The crystals are isomorphous with T3R3f complexes of phenolic derivatives as well as with uncomplexed forms. Unlike the structures of complexes with phenol, m-cresol, resorcinol, 4'-hydroxyacetanilide, and methylparaben, which bind one phenolic derivative molecule per R- or Rf-state monomer, two molecules of 4-hydroxybenzamide are bound by each Rf-state monomer. The presence of the second guest molecule results in an extensive hydrogen bonding network, mediated by water molecules, between the T- and Rf-state trimers and adds stability to the formation of the hexamer. The only access to these second sites is through three symmetry-related, narrow channels that originate on the surface of the T-state trimer. Although the conformation of the backbone atoms of the monomers is nearly identical to that of other T3R3f hexamers, significant changes are observed in the conformations of side chains in the vicinity of the second binding site. The side chain of the T-state A11 Cys residue, which forms a disulfide bond to A6 Cys in the same monomer, is observed in two discrete conformations; two discrete conformations are also present for the entire A8 Thr residue in the Rf-state monomer. A procedure is also described for an alternate method of interframe scaling and merging intensity data from an image plate detector.

Benzamides↗
PubMed1993

Absence of an effect of the lithium-induced increase in cyclic GMP on the cyclic GMP-stimulated phosphodiesterase (PDE II). Evidence for cyclic AMP-specific hydrolysis.

Chronic treatment of rats with LiCl is known to induce a decrease in cAMP, while this decrease has also been found to occur together with both a simultaneous increase in total cortical phosphodiesterase (PDE; EC 3.1.4.17) activity and a concomitant increase in cGMP. These studies have implicated an involvement of PDE in lithium (Li+) action and it has been suggested that cGMP and the cGMP-stimulated PDE may be instrumental in the observed effects of Li+ on cAMP. In this study, three isozymes of PDE were isolated and identified from rat cortex and their activity determined, together with simultaneous measurement of cAMP and cGMP, after chronic treatment with oral LiCl (0.35% m/m). Li+ treatment exerted profound effects on cyclic nucleotides in the cortex, inducing significant suppression of cAMP while increasing cGMP levels. However, the ion only induced a slight but insignificant increase in the activities of the three PDE isozymes. To confirm these observations, methylparaben (MPB), a drug demonstrating both an ability to induce a selective stimulation of cAMP-specific PDE and also to lower intracellular levels of cGMP, was co-administration orally (0.4% m/m) with Li+ over the same period. This combination emphasized certain actions of Li+ not noted with Li+ alone. MPB inhibited the Li(+)-induced increase in cGMP, yet did not prevent the ion from decreasing cAMP. However, the combination of Li+ and MPB engendered a synergistic 100% increase in the activity of the membrane-bound, cAMP-specific PDE, PDE IV. This combination also produced a significant suppression of cAMP, while no reduction in cGMP was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed2004

HPLC determination of estradiol, its degradation product, and preservatives in new topical formulation Estrogel HBF.

This paper deals with the development of a novel method for simultaneous determination of estradiol, its degradation product estrone, and two preservatives, methylparaben and propylparaben, in the topical preparation Estradiol HBF. After optimization of the analytical conditions the method was validated and applied in studies of the stability of the topical preparation Estrogel HBF. Separation of all these compounds was performed on a Supelco Discovery C18 (250 mm x 3.0 mm, 5 microm) analytical column. A mixture of acetonitrile, methanol, and water (23:24:53 v/ v) was chosen as mobile phase. UV absorbance at 225 nm was used for detection and quantitation of analytes. The total analysis time was less than 12 min at a flow rate of 0.9 mL min(-1). All the compounds were isolated from the topical gel by simple extraction with an acetonitrile solution of hydrocortisone, as internal standard, and using sonication and centrifugation thereafter. The supernatant was injected directly on to the analytical column. The recovery of the procedure was from 96.9 to 100.4%. Validation of method according international guidelines was successfully performed.

Administration, Topical↗