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Biomedical subjects

J K Seydel

Publications and source records attributed to J K Seydel.

At least 19 recordsLinked to original sources
PubMed1992

A time hierarchy-based model for kinetics of drug disposition and its use in quantitative structure-activity relationships.

By using the time hierarchy of the processes determining the fate of drugs in biosystems (absorption, transport, distribution, protein binding, and elimination), a one-compartment open model is formulated at a subcellular level for the disposition phase of pharmacokinetics. The resulting disposition function describes the kinetics of the intracellular disposition of drugs as determined by their hydrophobicity, acidity or basicity, affinity to proteins, and rate parameters of elimination. Structure-activity relationships, based on the function with incorporated extrathermodynamic relations, fit the literature data well (fixed-time bioactivity-hydrophobicity profiles, kinetics of microbial degradation of organic compounds, and kinetics of analgesic effects of fentanyl derivatives in rats). Application of the approach, creating a basis for the construction of model-based quantitative structure-time-activity relationship, to biosystems of varying complexity is discussed.

Animals↗
PubMed1992

Penetration of rifampicin into the cerebrospinal fluid of adults with uninflamed meninges.

The penetration of rifampicin into CSF was studied in seven patients who had undergone external ventriculostomy for occlusive hydrocephalus without major disturbance of the blood-CSF barrier. After the first dose of rifampicin 600 mg i.v. over 3 h, blood and CSF concentrations were determined serially by HPLC. Peak CSF concentrations obtained 0-8 h (median = 1 h) after the end of the infusion ranged from 0.57 to 1.24 mg/L (median = 0.73 mg/L). Elimination from CSF was slower than from serum (T1/2 beta CSF: 9.1-21.0 h (median = 14.5 h, n = 5); T1/2 beta serum: 2.2-5.8 h (median = 3.6 h, n = 7)). Based on the ratios of the areas under the concentration-time curves in CSF and serum, the overall penetration of rifampicin into CSF was 0.13-0.42 (median = 0.22). These results demonstrate effective CSF penetration and favourable pharmacokinetics of rifampicin in the absence of meningeal inflammation. They support the use of rifampicin as part of a combination therapy not only for tuberculosis of the central nervous system (CNS), but also for staphylococcal and listerial infections of the CNS in which there may be little meningeal inflammation.

Aged↗
PubMed1992

Development of effective drug combinations for the inhibition of multiply resistant mycobacteria, especially of the Mycobacterium avium complex.

Rationally designed combinations of rifampicin (RAMP) and thiacetazone plus isonicotinic acid hydrazide and/or ethambutol are highly effective in the treatment of patients (including HIV-positive) infected with multiply resistant mycobacteria of the Mycobacterium avium complex (MAC). Clinical results are very promising. The high efficacy of these combinations is due to the synergistic potentiation of single-drug activities. As soon as rifabutin is marketed, it should replace RAMP in the combination treatment of patients with highly RAMP-resistant MAC bacteria.

Chromatography, High Pressure Liquid↗
PubMed1992

[A new, highly synergistic drug combination for the treatment of infections with multiresistant mycobacteria, especially the mycobacterium avium complex].

Rationally designed combinations of rifampicin/thiacetazone plus isoniazid and/or ethambutol are highly effective in the treatment of patients (including HIV-pos.) infected with multiply resistant mycobacteria of the M. avium complex (MAC). Clinical results are very promising. The high efficacy of these combinations is due to the synergistic potentiation of single drug activities. As soon as rifabutin is marketed it should replace rifampicin in the combination treatment of patients with highly rifampicin-resistant MAC bacteria.

Acquired Immunodeficiency Syndrome↗
PubMed1992

Critical comments on the treatment of leprosy and other mycobacterial infections with clofazimine.

The usefulness of clofazimine (CLO, CAS 2030-63-9) in the treatment of mycobacterial infections with special emphasis on treatment of leprosy is critically discussed. Skin discolouration which decreases compliance, placenta passage, excretion in mother's milk which endanger the embryo or baby respectively, saturation kinetics in absorption and difficulties to determine free drug concentration are severe problems. The observed antagonism in the combination of CLO with other drugs, especially with dapsone, is another argument against its application in the therapy of mycobacterial infections. In Germany CLO has not been approved by the Bundesgesundheitsamt.

Clofazimine↗
PubMed1991

Interaction of prostaglandin E1 with alpha-cyclodextrin in aqueous systems: stability of the inclusion complex.

Prostavasin, an inclusion complex of prostaglandin E1 (PGE1) with alpha-cyclodextrin (alpha-CD), is used in the therapy of thrombosis. Nuclear magnetic resonance measurements have been made to study the interaction of PGE1 with alpha-CD. The observed interaction (chemical shift) and the derived dissociation constant prove that only weak interaction forces are operative and that complete dissociation occurs upon dilution.

Alprostadil↗
PubMed1991

Pyrimethamin-resistant Plasmodium falciparum lack cross-resistance to methotrexate and 2,4-diamino-5-(substituted benzyl) pyrimidines.

Methotrexate resistance induced in cultured Plasmodium falciparum depends on an altered dihydrofolate reductase with decreased affinity for methotrexate as well as for pyrimethamine. In contrast, pyrimethamine-resistant field isolates of P. falciparum lack cross-resistance to methotrexate and 2,4-diamino-5-(substituted benzyl) pyrimidines. The structure of the latter class was optimized by the use of trimethoprim as a lead and the substitution of methoxy groups at the benzyl ring by 3-(4'-aminophenyl-4-sulfonylphenylamino)propoxy or by (4'-aminophenyl-4-sulfonylphenyl)methoxy, which resulted in antimalarials of high potency. The efficiency of these newly designed 2,4-diamino-5-(substituted benzyl) pyrimidines was confirmed by their strong inhibitory effect on plasmodial dihydrofolate reductase as well as by in vitro screening against drug-sensitive and -resistant strains of P. falciparum.

Animals↗
PubMed1991

A kinetic description of the fate of chemicals in biosystems.

A simple kinetic description of the fate of low-molecular-weight compounds in biosystems was derived using the mass action law. Michaelis-Menten kinetics of enzymatic reactions was considered with respect to its two boundary cases, namely first- and zero-order kinetics. Absorption, membrane accumulation, non-covalent protein binding, biotransformation, and excretion have been included in the model, with only the last two steps being considered as time-dependent on the pertinent time scale of hours and days. This time hierarchy allowed for simplification of the resulting expression. In accordance with the results of uptake experiments and contrary to previous approaches, transport of organic molecules into the cell was not considered as the rate-limiting step. The decisive compound properties were found to be hydrophobicity and the intrinsic rate parameters of biotransformation and excretion. The model was applied to the elucidation of the dependence of the observed biotransformation rate parameters on hydrophobicity. The resulting equations are consistent with literature data.

Biotransformation↗
PubMed1990

Application of bacterial growth kinetics to in vitro toxicity assessment of substituted phenols and anilines.

Bacterial growth kinetics were applied to determine toxicity of substituted phenols and anilines serving as model toxicants. The effects observed on Escherichia coli can be quantified reliably. Additional information is obtained about the onset, the duration, and the time course of the toxic action. For most compounds under study a uniform mode of toxicity was observed, but multihalogen-and/or nitrosubstituted phenols differ in toxicity pattern. Possible reasons for the change in mechanism were examined. A comparison with published quantitative data for fish toxicity of halogenated phenols indicates good agreement with toxic effects observed in E. coli cultures. This may lead to the possibility of replacing the more costly, less stable fish test system by this simple and reliable in vitro test system.

Aniline Compounds↗
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

In vitro and in vivo experiments with the new inhibitor of mycobacterium leprae brodimoprim alone and in combination with dapsone.

The antibacterial effect of brodimoprim alone and in combination with dapsone has been studied in vitro in cell-free systems and in whole mycobacterial cells as well as in vivo in mice and humans. The obtained inhibitory effects in vitro and in vivo against model mycobacterial strains and M. leprae, the pharmacokinetic properties in human and its synergistic effect with the most used drug in the chemotherapy of leprosy, dapsone, make brodimoprim a promising candidate in the therapy of leprosy.

Adenosine Triphosphate↗
PubMed1989

Preparation and biological activity of new substituted antimalarial diaminodiphenylsulfones.

Starting from 4,4'-diamino-diphenylsulfone (DDS) as a lead structure, new 2-substituted analogues as well as new 2-substituted 4-alkylamino-4'-amino diphenylsulfones have been designed and synthetized in different ways. This has led to compounds the inhibitory activity of which against 7,8-dihydropteroic acid synthase of plasmodia and mycobacteria is clearly superior to that of sulfadoxine and in most cases to that of DDS. Of special interest is 4'-amino-4-n-propylamino-2-methyl-diphenylsulfone. Together with inhibitors of 7,8-dihydrofolate reductase in vitro and in vivo it possesses a marked synergistic inhibitory activity against plasmodia. In contrast to DDS in doses up to 200 mg/kg p.o. (cat) no methemoglobin formation is observed. The compound has been selected for further studies.

Animals↗
PubMed1989

Studies on 2,3,N,N'-substituted 4,4'-diaminodiphenylsulfones as potential antimalarial agents.

A series of new 4,4'-diaminodiphenylsulfones substituted at 2 and 3 position and also at primary amino group of the phenyl rings have been synthesized and evaluated for their antimalarial activity against Plasmodium berghei infection in mice. Some of these compounds were active and showed complete inhibition of parasitaemia which included 7a1-7a4, 7b3, 7b4 and 16a at 1 mg/kg i.p. for 4 days and 16a, at 0.3 mg/kg for 4 days. Some compounds tested for their synthetase inhibitory action in cell-free system isolated from P. berghei (7b1, 7b2 and 8b2) were found to be more active than diaminodiphenylsulphone. The difference in order of activity between these in vivo and in vitro tests may be due to differences in their pharmacokinetic properties.

Animals↗