Search results for "metabolite"
showing 10 items of 551 documents
Computer simulations of bioequivalence trials: selection of design and analyte in BCS drugs with first-pass hepatic metabolism: linear kinetics (I).
2008
Modeling and simulation approaches are useful tools to assess the potential outcome of different scenarios in bioequivalence studies. The aim of this study is to propose a new and improved semi-physiological model for bioequivalence trial simulations and apply it for all BCS (Biopharmaceutic Classification System) drug classes with non-saturated first-pass hepatic metabolism. The semi-physiological model was developed in NONMEM VI to simulate bioequivalence trials. Parent drug and metabolite levels for both reference and test were simulated. Eight types of drugs (with high or low permeability and high or low solubility (class I to IV) and high or low intrinsic clearance) were considered in …
5-Fluorouracil Buccal Tablets for Locoregional Chemotherapy of Oral Squamous Cell Carcinoma: Formulation, Drug Release and Histological Effects on Re…
2010
5-Fluorouracil (5-FU) is currently used for treatment of oral squamous cell carcinoma (OSCC). 5-FU is given by i.v. although the systemic administration is associated with severe toxic effects and no topical formulations of 5-FU for buccal drug delivery have been reported. In this study we would report the development of buccal tablets suitable for direct application of low-doses of 5-FU on cancer lesions. The topical administration could be effective on tumor area while systemic undesired side effects are avoided. Preliminarily, the limited tendency of 5-FU to cross the buccal tissue was established using reconstituted human oral epithelium (RHOE, in vitro) and porcine buccal mucosa (ex vi…
Medium-Term Culture of Primary Oral Squamous Cell Carcinoma in a Three- Dimensional Model: Effects on Cell Survival Following Topical 5-Fluororacile …
2012
Since the activity of several conventional anticancer drugs is restricted by resistance mechanisms and dose-limiting side-effects, the design of formulations for local application on malignant lesions seems to be an efficient and promising drug delivery approach. In this study, the effect of locally applied 5-FU on cell death was evaluated both in a SCC4/HEK001 model and in a newly proposed 3D outgrowth model of oral squamous cell carcinoma (OSCC). Initially, the optimal drug dose was established by delivery of solutions containing different amounts of 5-FU. The solution containing 1% (w/v) of 5-FU resulted effective in inducing cell death with complete eradication of cell colonies. Buccal …
Biochemical approach on the conservation of drug molecules during hair fiber formation
1997
A biochemical concept for the endogenous incorporation of drug molecules into growing hair is presented. It is based on the principles of transport across biomembranes, on the principles of biotransformation and drug melanin affinity. The approach gives explanations for current observations in hair analysis, which up to date have not been understood sufficiently. Phenomena such as the ratio of parent drug to metabolite in hair, the dependence of incorporation on the physico-chemical properties of the drug, the independence of drug incorporation on active melanogenesis (incorporation into non-pigmented hair) as well as the dependence of drug content on hair pigmentation are elucidated.
Distribution of clozapine and desmethylclozapine between blood and brain in rats.
1999
Desmethylclozapine is the major metabolite of clozapine in serum. Although the metabolite is pharmacologically active in vitro, the occurrence of desmethylclozapine in brain under steady-state conditions and its role for clinical actions of clozapine are unclear. In this study 20 male Sprague-Dawley rats received five oral doses of clozapine 20 mg/kg at 1.5-h intervals. At 0.5, 1, 2 and 5 h after the last administration, at a time four animals were killed for analysis of clozapine and desmethylclozapine concentrations in serum and brain. The treatment yielded steady-state serum concentrations of clozapine that are considered as therapeutically effective in man. Desmethylclozapine concentrat…
Perspiration versus saliva--basic aspects concerning their use in roadside drug testing.
1999
Various aspects concerning the practical application and forensic interpretation of data obtained by saliva drug testing and drug monitoring from the skin surface are discussed. Basic information on the composition of saliva and skin secretions and their particular transport mechanisms, as far as known, are given. For drugs of abuse secretion into saliva is suggested to be by passive diffusion and to depend on lipid solubility, pKa, plasma protein binding and on the pH of saliva. Drug molecules from blood are considered to reach the skin surface by various routes such as by sweat and sebum as well as by inter- and/or transcellular diffusion. The role of the stratum corneum as a temporary dr…
Mechanisms of Toxification and Detoxification which Challenge Drug Candidates and Drugs
2007
Almost all drugs are metabolized in the human organism. In most cases this changes the toxicity, sometimes by toxification, sometimes by detoxification. For obvious ethical reasons, the toxicity cannot be experimentally studied in human beings. In systems available for toxicity studies such as whole animals or human or animal cells in culture, the drug metabolism is substantially different from that in the human organism. Risk assessment for human therefore requires knowledge of drug metabolism, its differences between systems, and the consequences for toxicity. In phase 1 of drug metabolism (oxidoreductions and hydrolyses) drugs are often toxified. This is especially the case if the result…
Drug-metabolizing enzymes in the skin of man, rat, and pig.
2007
The mammalian skin has long been considered to be poor in drug metabolism. However, many reports clearly show that most drug metabolizing enzymes also occur in the mammalian skin albeit at relatively low specific activities. This review summarizes the current state of knowledge on drug metabolizing enzymes in the skin of human, rat, and pig, the latter, because it is often taken as a model for human skin on grounds of anatomical similarities. However only little is known about drug metabolizing enzymes in pig skin. Interestingly, some cytochromes P450 (CYP) have been observed in the rat skin which are not expressed in the rat liver, such as CYP 2B12 and CYP2D4. As far as investigated most d…
Induction of Drug Transporters Alters Disposition of Risperidone - A Study in Mice
2010
Pharmacokinetic interactions, e.g. modulation of drug transporters like P-glycoprotein at the blood-brain barrier, can be a reason for treatment non-response. This study focuses on the influence of induction of drug transporters on the disposition of the antipsychotic drugs risperidone and 9-hydroxyrisperidone. Brain and serum concentrations of risperidone and its active metabolite 9-hydroxyrisperidone, which are known P-glycoprotein substrates, were measured after drug transporter induction with rifampicin, dexamethasone or 5-pregnene-3beta-ol-20-on-16alpha-carbonitrile using high performance liquid chromatography. Disposition of risperidone and 9-hydroxyrisperidone was dramatically decrea…
Metabolic Adaptation and Protein Complexes in Prokaryotes.
2012
Protein complexes are classified and have been charted in several large-scale screening studies in prokaryotes. These complexes are organized in a factory-like fashion to optimize protein production and metabolism. Central components are conserved between different prokaryotes; major complexes involve carbohydrate, amino acid, fatty acid and nucleotide metabolism. Metabolic adaptation changes protein complexes according to environmental conditions. Protein modification depends on specific modifying enzymes. Proteins such as trigger enzymes display condition-dependent adaptation to different functions by participating in several complexes. Several bacterial pathogens adapt rapidly to intrace…