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Biomedical subjects

B W Müller

Publications and source records attributed to B W Müller.

65 records · Page 4Linked to original sources
PubMed1990

Effect of cyclodextrin derivatives on indomethacin stability in aqueous solution.

The effect of various cyclodextrins (CD) and cyclodextrin derivatives on indomethacin stability in phosphate buffer, pH 7.4, was investigated. The influence of CD-ring size, type of substituent, degree of substitution, substitution pattern, and influence of CD concentration were monitored. The indomethacin complex in solution was studied by 1H-NMR spectroscopy to develop a molecular inclusion model. The most favorable ring size for the stabilization of indomethacin was the beta-CD. The beta-CD derivatives inhibited the hydrolysis of indomethacin more effectively than the parent CD. Among the studied CD derivatives, those with lipophilic substituents, such as ethyl or methyl, were superior to those with hydrophilic substitutents. The more hydroxyl groups of the glucose moiety are substituted, the better is the stabilizing effect. Further, the p-chlorobenzoic part of the indomethacin molecule is included in the CD channel.

2-Hydroxypropyl-beta-cyclodextrin↗
PubMed1990

Stability of gonadorelin and triptorelin in aqueous solution.

The influence of pH, temperature, various buffer species at different concentrations, and ionic strength on the stability of gonadorelin and triptorelin in aqueous solution has been studied using stability-indicating high-performance liquid chromatographic methods. The degradation behavior of both peptides is similar. The maximum stability of both peptides was shown to be at an approximate pH of 5.0. Acetate has the most favorable effect on stability, while phosphate causes higher degradation. Varying the concentration of acetate buffer does not affect the degradation behavior of the peptides. A higher phosphate concentration in buffer solutions causes higher degradation, however. The ionic strength of buffer solutions has no significant influence on stability. Solutions of gonadorelin and triptorelin, respectively, buffered with acetate (0.1 M, pH 5.0) with 3% (w/v) mannitol as an additive show a predicted t90% of 9.0 years and 7.7 years at 20 degrees C, respectively.

Acetates↗
PubMed1986

Hydroxypropyl-beta-cyclodextrin derivatives: influence of average degree of substitution on complexing ability and surface activity.

The average degree of substitution of mixtures of hydroxypropyl-beta-cyclodextrin derivatives has a large influence on the complexing abilities and physiochemical properties of the derivatives. A low degree of substitution is preferable, since these derivatives show the best complexing properties and, at the same time, low surface activities.

Chemistry, Pharmaceutical↗
PubMed1984

Particle size analysis of latex suspensions and microemulsions by photon correlation spectroscopy.

The particle size in microemulsions and other highly dispersed systems was determined by means of photon correlation spectroscopy (PCS). As PCS cannot be applied to highly concentrated dispersed phases, the measurement accuracy was tested for its dependence on the particle concentration using latex suspensions. The data obtained by clipping and scaling were compared. The particle size determination was expected to provide information about the influence of the structure of the surfactant system on microemulsions, using a homologous alcohol series as cosurfactant and potassium oleate as surfactant. In this system the region of solubilization is characteristically divided from the region of microemulsification by a zone of instability. Furthermore, there are distinct differences in mean particle sizes between microemulsions (9-30 nm) and micellar solutions (4-6 nm).

Alcohols↗
PubMed1984

Particle size distributions and particle size alterations in microemulsions.

Several component diagrams for different alcohols as cosurfactants and potassium oleate as the surfactant were investigated. Between the regions of the water-in-oil microemulsion and the micellar solution (reverse micelles), and diagrams showed a zone of instability which was determined by particle size analysis by means of photon correlation spectroscopy (PCS). The polydispersity of the internal phase was determined at the instant of microemulsion formation and after fixed intervals of storage. At the edge of the microemulsion region, a rapid increase in particle size due to coalescence followed by breaking was observed. If a slow transition toward the region of solubilization could be seen by a slow decrease of the droplet size, coalescence was observed after storage. In the middle of the microemulsion region, the particle radius, however, was almost constant for a long interval. The velocity of the microemulsion formation depended on the alcohol used. In some cases a very fast formation (milliseconds) was observed; in others, macroemulsions were formed which became transparent within a few hours or days. PCS was used to follow the dynamic process of formation and breaking of such systems with droplet diameters of 5-200 nm by obtaining the mean hydrodynamic diameters. Distribution curves were calculated by the Laplace transform of the correlation function. The practicability of the method was demonstrated with mono- and polydispersed latex suspensions and microemulsions.

Emulsions↗
PubMed1984

[Comparative studies on the bioavailability of paracetamol from suppositories].

In a comparative study with 10 healthy male volunteers three paracetamol preparations (two commercial products and one preparation with micronized paracetamol) are tested. No differences in absorption and elimination rate as well as in bioavailability are determined. Reported variations in absorption rate and bioavailability can be explained by different vehicle volumes which were applicated. The vehicle volume, that means the dimension of the rectal absorption area is main factor for interpretation of pharmacokinetic data. The micronization of the drug leads to a sustained release. This result is in correlation with in vitro studies.

Acetaminophen↗
PubMed1983

Cephalosporin antibiotics. Synthesis and antimicrobial activity of 7 beta-[2-(5-amino-1,2,4-thiadiazol-3-yl)-2-oxyiminoacetamido]cephalosporin derivatives.

Cephalosporins with a 7 beta-[2-(5-amino-1,2,4-thiadiazol-3-yl) -2-oxyiminoacetamido] side chain were synthesized and their in vitro inhibitory potency was established. The compounds exhibit a strong antibacterial activity against various Gram-positive and Gram-negative bacteria. The antimicrobial activity is related to the oxime-substituent R1 and the C-3 substituent R2. Selected amino-1,2,4-thiadiazolyl-cephems 1 show a prolonged half-life in mice.

Animals↗
PubMed1979

Semisynthetic bicyclomycin derivatives: preparation and antibacterial evaluation.

A number of semisynthetic bicyclomycin derivatives have been prepared by modifications at various sites of the molecule. The preparation, characterization and antimicrobial evaluation of the new compounds is described. In contrast to bicyclomycin itself, the new derivatives 48 and 58 are also active against Proteus species. Otherwise, the antibacterial potency of the bicyclomycin molecule was found to be very sensitive to structural changes.

Animals↗
PubMedDate not supplied

Production of drug loaded microparticles by the use of supercritical gases with the aerosol solvent extraction system (ASES) process.

The aerosol solvent extraction system (ASES) uses a supercritical gas as non-solvent for an organic solution of drug and polymer in order to form microparticles by a flocculation process. Due to the miscibility of organic solvent and supercritical gas phase, microparticles with residual organic solvents below 30 ppm are formed. This principle was tested to encapsulate model drugs such as hyoscine butylbromide, indomethacin, piroxicam and thymopentin. As a carrier, the polymer poly-L-lactide was used. The resulting microparticles were investigated with regard to particle formation, morphology, particle size, size distribution, and drug loading. With decreasing, polarity of the incorporated drug, an increasing extraction occurs which lowers the drug loading of the microparticles. The extraction capacity of the gas phase depends on temperature and pressure which determines density and polarity of the gas. The obtained results show that the production conditions have to be optimized for each drug/polymer combination. Totally non-polar drugs are completely extracted together with the organic solvent, however, polar drugs, and here especially peptides and proteins, are easy to incorporate with the ASES process.

Aerosols↗