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G F Schneider

Publications and source records attributed to G F Schneider.

10 recordsLinked to original sources
PubMed1981

[Bioavailability of theophylline in a new oral sustained-release preparation (author's transl)].

On the basis of biopharmaceutic-pharmacokinetic and galenic aspects a new sustained-release preparation of theophylline according to the "divided-dose" principle was developed. The technological procedure used allows a reproducible manufacture of a stable product with narrow limits of pharmaceutical quality. The bioavailability of the sustained-release pellets in a dose corresponding to 350 mg active principle is examined in comparison to an aqueous solution or retard-tablet formulation on the marked (containing 260 mg drug/dose), respectively, after single or multiple dose administration to 7 healthy volunteers. The relative bioavailability of the new formulation is about 100%. During chronic application the controlled drug delivery from the sustained-release pellets warrants only slight fluctuations of plasma levels by avoiding peak concentrations. Formulations with a dosage of 200, 350 or 500 mg, respectively, allow adaptation of continuous plasma levels in the therapeutic range between 5--20 micrograms/ml according to the therapeutic necessities of a patient.

Adult↗
PubMed1976

[Studies on the absorption of benzilic acid esters of homologous dimethyl-(2-hydroxyethyl)-alkylammonium bromides through buccal mucosa. 5th communication: On optimum bioavailability of homologous quaternary ammonium compounds (author's transl)].

Distribution studies in vitro predict increasing absorption rates in vivo with increasing distribution coefficients up to a limiting value. Buccal absorption tests with homologous, quaternary cholinesterbromides of benzilic acid do not confirm this hypothesis. The reasons could be the rather hydrophilic properties of the mucosal membranes and thus adsorption of drug to the mucosa. The evaluation of results with undissociated homologous carboxylic acids, however, shows a good correlation between the prediction from in vitro studies and the buccal absorption test.

Absorption↗
PubMed1975

[The optimization of the availability of homologous quaternary ammonium compounds. 2. In vitro studies on the partition of homologous benzilic acid esters of dimethyl-(2-hydroxyethyl)-alkylammonium bromides].

The partition of homologous quaternary esters of benzilic acid is studied in a modified three-phase model according to Schulmann (water-n-octanol-water). The logarithms of the partition coefficients of the compounds increase linearly with increasing alkyl chain. The rate determining step for the interphase transport of hydrophilic compound is the diffusion through the organic diffusion layer. The rate constants for the transfer from the aqueous to the organic phase increase linearly with the corresponding partition coefficient, whereas the rate constants for the reverse reaction are not influenced. With increasing chain length the diffusion through the aqueous diffusion layer becomes rate determining for the interphase transport. Thus the rate constants for the transfer from the aqueous to the organic phase are independent of partition coefficients. The rate constants for the reverse transfer are inversely proportional to the corresponding partition coefficients. The half-lives of the transfer of the homologous compounds under sink conditions show a minimum between the heptyl and octyl derivative. The equilibration time decreases with increasing agitation, concentration and temperature. The significance of the results for biological problems is discussed.

Benzilates↗
PubMed1975

[Optimating the availability of homologous quaternary ammonium compounds/3rd communication: The influence of salts on in vitro distribution of benzilic acid esters of homologous dimethyl-(2-hydroxyethyl)-alkyl-ammoniumbromides (author's transl)].

The addition of NaBr, Na-butansulfonate or Na-trichloracetat increases the partition coefficients of homologous quaternary cholinesters of benzilic acid between n-octanol and water. In a three-phase model (water/n-octanol/water) thus the rates of equilibration increase considerably for hydrophilic compounds.

Benzilates↗