Showing papers by "Ulrike Holzgrabe published in 2009"

Penetration of antibacterials into bone: pharmacokinetic, pharmacodynamic and bioanalytical considerations.

Abstract: Antibacterials play a key role in the treatment of bone infections and appropriate surgical prophylaxis. The rate and extent of penetration of antimicrobials into bone has been assessed and shown to be important for successful treatment in numerous studies. However, no recent review or critical evaluation of the analytical techniques is available. This review compares established and new sample preparation and analytical methods to measure bone concentrations. We performed a systematic literature search in MEDLINE, EMBASE, conference abstracts and references from published articles on bone penetration of antibacterials. This article focuses on the standardization of drug analysis in bone, the extent and rate of bone penetration of antibacterials, and the design, evaluation and reporting techniques of pharmacokinetic studies of bone penetration. The focus is on studies conducted between 1998 and 2007, since a previous review was published in 1999. WinNonlin® Professional version 5.0.1 software was used for statistics. Very different methods for sample preparation, drug analysis, data handling and reporting have been employed in bone penetration studies. There is substantial variability in the reported mean bone penetration between drugs and between different studies of the same drug. Quinolones, macrolides and linezolid have mean bone:serum concentration ratios that are commonly between 0.3 and 1.2, and higher ratios have been found for azithromycin (bone concentration in mg/kg of total bone). The ratios are usually between 0.15 and 0.3 for cephalosporins and glycopeptides, and between 0.1 and 0.3 for penicillins. Cephalosporins and penicillins have shown significantly lower (p<0.05) concentration ratios than linezolid. For 20 of 25 different drugs, the ratios were higher for cancellous bone than for cortical bone. The available data show a larger extent of bone penetration for quinolones, macrolides and linezolid than for β-lactams. The bone penetration of penicillins and cephalosporins was significantly lower than that of linezolid. Guidelines on sample preparation, drug analysis, study design and pharmacokinetic evaluation of bone penetration studies are vitally needed.

Dualsteric GPCR targeting: a novel route to binding and signaling pathway selectivity

Abstract: Selective modulation of cell function by G protein-coupled receptor (GPCR) activation is highly desirable for basic research and therapy but difficult to achieve. We present a novel strategy toward this goal using muscarinic acetylcholine receptors as a model. The five subtypes bind their physiological transmitter in the highly conserved orthosteric site within the transmembrane domains of the receptors. Orthosteric muscarinic activators have no binding selectivity and poor signaling specificity. There is a less well conserved allosteric site at the extracellular entrance of the binding pocket. To gain subtype-selective receptor activation, we synthesized two hybrids fusing a highly potent oxotremorine-like orthosteric activator with M(2)-selective bis(ammonio)alkane-type allosteric fragments. Radioligand binding in wild-type and mutant receptors supplemented by receptor docking simulations proved M(2) selective and true allosteric/orthosteric binding. G protein activation measurements using orthosteric and allosteric blockers identified the orthosteric part of the hybrid to engender receptor activation. Hybrid-induced dynamic mass redistribution in CHO-hM(2) cells disclosed pathway-specific signaling. Selective receptor activation (M(2)>M(1)>M(3)) was verified in living tissue preparations. As allosteric sites are increasingly recognized on GPCRs, the dualsteric concept of GPCR targeting represents a new avenue toward potent agonists for selective receptor and signaling pathway activation.

Structure-Activity Relationship and Studies on the Molecular Mechanism of Leishmanicidal N,C-Coupled Arylisoquinolinium Salts

Abstract: Alternative drugs against leishmaniasis are desperately needed. Antimonials, the main chemotherapeutic tool, cause serious side effects and promote chemoresistance. We previously demonstrated that representatives of N,C-linked arylisoquinolines are promising leishmanicidal drug candidates. We now performed structure−activity relationship studies varying the aryl portion of our lead substrate. The new series of compounds show an enhanced selectivity against Leishmania major in comparison to their major host cell, the macrophage. Our results suggest that the arylisoquinolinium salts decrease the macrophage infection rate acting directly on the intracellular parasites. However, the activity of the 4′-i-propyl derivative might also involve the modulation of cytokine and nitric oxide production by host macrophages. Additionally, this isoquinoline acts synergistically with amphotericin B and does not interact with drug-metabolizing cytochrome P450 enzymes involved in the metabolism of antileishmanial drugs. The...

A small-molecule inhibitor of Nipah virus envelope protein-mediated membrane fusion.

Abstract: Nipah virus (NiV), a highly pathogenic paramyxovirus, causes respiratory disease in pigs and severe febrile encephalitis in humans with high mortality rates. On the basis of the structural similarity of viral fusion (F) proteins within the family Paramyxoviridae, we designed and tested 18 quinolone derivatives in a NiV and measles virus (MV) envelope protein-based fusion assay beside evaluation of cytotoxicity. We found five compounds successfully inhibiting NiV envelope protein-induced cell fusion. The most active molecules (19 and 20), which also inhibit the syncytium formation induced by infectious NiV and show a low cytotoxicity in Vero cells, represent a promising lead quinolone-type compound structure. Molecular modeling indicated that compound 19 fits well into a particular protein cavity present on the NiV F protein that is important for the fusion process.

Penetration of Moxifloxacin into Bone Evaluated by Monte Carlo Simulation

Abstract: Moxifloxacin is a fluoroquinolone with a broad spectrum of activity and good penetration into many tissues, including bone. Penetration of moxifloxacin into bone has not yet been studied using compartmental modeling techniques. Therefore, we determined the rate and extent of bone penetration by moxifloxacin and evaluated its pharmacodynamic profile in bone via Monte Carlo simulation. Twenty-four patients (10 males, 14 females) undergoing total hip replacement received 400 mg moxifloxacin orally 2 to 7 h prior to surgery. Blood and bone specimens were collected. Bone samples were pulverized under liquid nitrogen by a cryogenic mill, including an internal standard. Drug concentrations were analyzed by high-performance liquid chromatography. We used ADAPT II (results reported), NONMEM, and WinBUGS for pharmacokinetic analysis. Monte Carlo simulation was performed to reverse engineer the necessary area under the free concentration-time curve f AUC SERUM /MIC in serum and total AUC BONE /MIC in bone for a successful clinical or microbiological outcome. The median (10% to 90% percentile for between-subject variability) of the AUC in bone divided by the AUC in serum (AUC BONE /AUC SERUM ) was 80% (51 to 126%) for cortical bone and 78% (42 to 144%) for cancellous bone. Equilibration between serum and bone was rapid. Moxifloxacin achieved robust (≥90%) probabilities of target attainment (PTAs) in serum, cortical bone, and cancellous bone up to MICs of ≤0.375 mg/liter based on the targets f AUC SERUM /MIC ≥ 40 and AUC BONE /MIC ≥ 33. Moxifloxacin showed high bone concentrations and a rapid equilibrium between bone and serum. The favorable PTAs compared to the 90%-inhibitory MIC of Staphylococcus aureus warrant future clinical trials on the effectiveness of moxifloxacin in the treatment of bone infections.

Bone Penetration of Amoxicillin and Clavulanic Acid Evaluated by Population Pharmacokinetics and Monte Carlo Simulation

Abstract: Amoxicillin (amoxicilline)-clavulanic acid has promising activity against pathogens that cause bone infections. We present the first evaluation of the bone penetration of a beta-lactam by population pharmacokinetics and pharmacodynamic profiling via Monte Carlo simulations. Twenty uninfected patients undergoing total hip replacement received a single intravenous infusion of 2,000 mg/200 mg amoxicillin-clavulanic acid before surgery. Blood and bone specimens were collected. Bone samples were pulverized under liquid nitrogen with a cryogenic mill, including an internal standard. The drug concentrations in serum and total bone were analyzed by liquid chromatography-tandem mass spectrometry. We used NONMEM and S-ADAPT for population pharmacokinetic analysis and a target time of the non-protein-bound drug concentration above the MIC for > or = 50% of the dosing interval for near-maximal bactericidal activity in serum. The median of the ratio of the area under the curve (AUC) for bone/AUC for serum was 20% (10th to 90th percentile for between-subject variability [variability], 16 to 25%) in cortical bone and 18% (variability, 11 to 29%) in cancellous bone for amoxicillin and 15% (variability, 11 to 21%) in cortical bone and 10% (variability, 5.1 to 21%) in cancellous bone for clavulanic acid. Analysis in S-ADAPT yielded similar results. The equilibration half-lives between serum and bone were 12 min for amoxicillin and 14 min for clavulanic acid. For a 30-min infusion of 2,000 mg/200 mg amoxicillin-clavulanic acid every 4 h, amoxicillin achieved robust (> or = 90%) probabilities of target attainment (PTAs) for MICs of < or = 12 mg/liter in serum and 2 to 3 mg/liter in bone and population PTAs above 95% against methicillin-susceptible Staphylococcus aureus in bone and serum. The AUC of amoxicillin-clavulanic acid was 5 to 10 times lower in bone than in serum, and amoxicillin-clavulanic acid achieved a rapid equilibrium and favorable population PTAs against pathogens commonly encountered in bone infections.

Competitive inhibition of renal tubular secretion of gemifloxacin by probenecid

Abstract: Probenecid interacts with transport processes of drugs at several sites in the body. For most quinolones, renal clearance is reduced by concomitant administration of probenecid. The interaction between gemifloxacin and probenecid has not yet been studied. We studied the extent, time course, site(s), and mechanism of this interaction. Seventeen healthy volunteers participated in a randomized, two-way crossover study. Subjects received 320 mg gemifloxacin as an oral tablet without and with 4.5 g probenecid divided in eight oral doses. Drug concentrations in plasma and urine were analyzed by liquid chromatography-tandem mass spectrometry. WinNonlin was used for noncompartmental analysis, compartmental modeling, and statistics, and NONMEM was used for visual predictive checks. Concomitant administration of probenecid increased plasma gemifloxacin concentrations and amounts excreted in urine compared to baseline amounts. Data are average estimates (percent coefficients of variation). Modeling showed a competitive inhibition of the renal tubular secretion of gemifloxacin by probenecid as the most likely mechanism of the interaction. The estimated K(m) and Vmax for the saturable part of renal elimination were 9.16 mg/liter (20%) and 113 mg/h (21%), respectively. Based on the molar ratio, the affinity for the renal transporter was 10-fold higher for gemifloxacin than for probenecid. Since probenecid reached an approximately 200-times-higher area under the molar concentration-time curve from 0 to 24 h than gemifloxacin, probenecid inhibited the active tubular secretion of gemifloxacin. Probenecid also reduced the nonrenal clearance of gemifloxacin from 25.2 (26%) to 21.0 (23%) liters/h. Probenecid inhibited the renal tubular secretion of gemifloxacin, most likely by a competitive mechanism, and slightly decreased nonrenal clearance of gemifloxacin.

New semiphysiological absorption model to assess the pharmacodynamic profile of cefuroxime axetil using nonparametric and parametric population pharmacokinetics

Abstract: Cefuroxime axetil is widely used to treat respiratory tract infections. We are not aware of a population pharmacokinetic (PK) model for cefuroxime axetil. Our objectives were to develop a semiphysiological population PK model and evaluate the pharmacodynamic profile for cefuroxime axetil. Twenty-four healthy volunteers received 250 mg oral cefuroxime as a suspension after a standardized breakfast. Liquid chromatography-tandem mass spectrometry was used for drug analysis, NONMEM and S-ADAPT (results reported) were used for parametric population PK modeling, and NPAG was used for nonparametric population PK modeling. Monte Carlo simulations were used to predict the duration for which the non-protein-bound-plasma concentration was above the MIC (fT(>MIC)). A model with one disposition compartment, a saturable and time-dependent drug release from the stomach, and fast drug absorption from the intestine yielded precise (r > 0.992) and unbiased curve fits and an excellent predictive performance. The apparent clearance was 21.7 liters/h (19.8% coefficient of variation [CV]) and the volume of distribution 38.7 liters (18.3% CV). Robust (>or=90%) probabilities of target attainment (PTAs) were achieved by 250 mg cefuroxime given every 12 h (q12h) or q8h for MICs of MIC) of >or=40% and for MICs of MIC) of >or=65%. For the >or=40% fT(>MIC) target, the PTAs for 250 mg cefuroxime q12h were >or=97.8% for Streptococcus pyogenes and penicillin-susceptible Streptococcus pneumoniae. Cefuroxime at 250 mg q12h or q8h achieved PTAs below 73% or 92%, respectively, for Haemophilus influenzae, Moraxella catarrhalis, and penicillin-intermediate S. pneumoniae for susceptibility data from various countries. Depending on the MIC distribution, 250 mg oral cefuroxime q8h instead of q12h should be considered, especially for more-severe infections that require near-maximal killing by cefuroxime.

Cerulenin analogues as inhibitors of efflux pumps in drug-resistant Candida albicans.

Abstract: Overexpression of the ABC transporters Cdr1 and Cdr2 or the major facilitator Mdr1 causes multidrug resistance in the human fungal pathogen Candida albicans. The fatty acid synthesis inhibitor cerulenin and the structurally unrelated Golgi transport inhibitor brefeldin A are substrates for both types of efflux pumps in Candida albicans. In an effort to overcome efflux pump-mediated drug resistance in Candida albicans, cerulenin analogues were generated using a variety of synthesis pathways. The so obtained cerulenin derivatives were tested on multidrug-resistant Candida albicans isolates which constitutively overexpress either Mdr1 or Cdr1 and Cdr2. Some of these compounds were found to decrease Mdr1-mediated resistance to brefeldin A up to eightfold compared to the control.

Meropenem-clavulanate: a new strategy for the treatment of tuberculosis?

Abstract: The Great White Plague: Mycobacterium tuberculosis, the bacteria causing tuberculosis, is a continuing threat to global health through the emergence of resistant strains and the lack of novel therapeutic agents. Recently reported results on this important work are highlighted.

Prediction of the oversulphated chondroitin sulphate contamination of unfractionated heparin by ATR-IR spectrophotometry.

Abstract: The detection of a contamination of heparin with oversulphated chondroitin sulphate (OSCS) was first analysed in an unfractionated heparin batch supplied to the US API-market in April 2006. OSCS is a semi-synthetic derivative of the natural occuring glycosaminoglycan chondroitin sulphate. Moreover some spectroscopic characteristics of the substance overlap with those of heparin, so that the infrared (IR) spectra are visually difficult to distinguish whereas (1)H-NMR (Nuclear Magnetic Resonance) spectroscopy or capillary electrophoresis (CE) provides identification by a simple visual inspection of either the spectrum or the electropherogram respectively. However, applying special tools of Multivariate Data Analysis (MVA) to the IR spectra an identification of the contaminated samples is possible. In detail a rapid Attenuation Total Reflectance-Infrared (ATR-IR) measurement was selected, which does not require any sample preparation. The result (contaminated or not contaminated) is predicted within a few minutes. A method transfer to mobile ATR-IR spectrometers seems to be possible. The analysis is based on the fact that the fingerprint of the OSCS IR spectrum (1st derivative) complies with a theoretically calculated principal component in the MVA.

Erkennung und Vermeidung von Arzneimittelfälschungen durch Verwendung adäquater Wirk- und Hilfsstoffe

Abstract: For the last years the number of cases of counterfeit drugs is substantially increasing. Beside the classical categories of counterfeits, being fake packaging, wrong or no active pharmaceutical ingredient (API) or the wrong amount of API, a fifth category occurred recently, i.e. APIs of low quality. The contaminated heparin which has lead to deaths in the United States is a representative case and will not be the last one. The fact that 80 % of the APIs are produced in China and India will foster this development. Thus, methods orthogonal to the pharmacopoeia methods, such as NMR-, Raman, and near-infrared spectroscopy as well as powder X-ray-diffractometry, should be additionally applied to ensure the identity and quality of the APIs.

Piperidone derivatives and medical uses thereof

Abstract: The present invention relates to compositions comprising 4-Oxo-piperidine-carboxylates and derivatives thereof, for example derivatives substituted with phenyl, nitrophenyl or benzyl groups. It also teaches the medical use of these and related compounds for treatment of retroviral diseases, in particular, HIV and HTLV, proliferative diseases, in particular CML and Trypanosomiasis.

Neue Antibiotika in Sicht

Abstract: In den letzten 40 Jahren wurden nur zwei neue Antibiotikagruppen aufgefunden, und zwar die Oxazolidinone (Linezolid) und die Lipopeptide (Daptomycin), die neue Zielstrukturen bedienen, um ihre bakerizide Wirkung zu entfalten. Ubrigens wurden beide Gruppen – wie auch die wenigen anderen Substanzen in der Pipeline wie Glycolipodepsipeptide (Ramoplanin), Pleuromutiline (Retapamulin) oder Glycosyltransferase-Inhibitoren (Moenomycin) – schon vor sehr langer Zeit aufgefunden, aber damals aus verschiedenerlei Grunden wie z.B. Toxizitat nicht weiterentwickelt.

Problem Arzneimittelfälschungen in Afrika und Südostasien. Gefälschte Antimalariamittel und mehr

Abstract: In Afrika und Sudostasien ist der Prozentsatz gefalschter Arzneimittel sehr hoch. Dies gilt insbesondere fur Antibiotika gegen Tropenkrankheiten. Grose analytische Anstrengungen in internationalen Konsortien, in denen Analytiker, Polizei, INTERPOL und Behorden zusammenarbeiten, sind notwendig, um Falschungen auf die Spur zu kommen und Falschern das Handwerk zu legen.

Wege aus der Malaria-Resistenz?

Abstract: Obgleich es zum ersten Mal berechtigte Hoffnung auf einen Malaria-Impfstoff gibt, ist es naturlich dennoch wichtig, potente Wirkstoffe gegen Malaria zu haben. Problem ist, dass es gegen immer mehr Antimalariamittel Resistenzen gibt, z.B. gegen die ganze Reihe der Substanzen, die sich von Chinin und Chloroquin ableiten.

Vitamin E. Alles ist im Fluss

Abstract: Die Literatur uber die Chemie, Physiologie, Biochemie und den therapeutischen Einsatz von Vitamin E ist unubersehbar. Erst kurzlich haben wir den antioxidativen Wirkmechanismus von Tocopherol vollstandig verstanden. Weniger wissen wir uber seine physiologischen Wirkungen und damit auch uber den moglichen Einsatz in Pravention und Therapie von Krankheiten wie Krebs, kardiovaskularen Erkrankungen oder Rheuma. Grose Metaanalysen haben keine Vorteile aufgezeigt, ja sogar eine leichte Erhohung der Mortalitat ergeben, so dass bei der Supplementierung mit hohen Dosen Vitamin E Vorsicht geboten ist.

Neue Hoffnung auf eine Malaria-Impfung

Abstract: Malaria ist auch heute noch weltweit eine der am weitesten verbreiteten parasitaren Erkrankungen, insbesondere in Afrika sudlich der Sahara. Sie verursacht jahrlich 300 Millionen Neuerkrankungen und 1 bis 3 Millionen Tote, zumeist unter Kindern im Alter unter 5 Jahren.