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  • 1
    ISSN: 1432-1041
    Keywords: Nimodipine ; Cimetidine ; Ranitidine ; pharmacokinetic interaction ; cytochrome P-450 ; healthy volunteers ; haemodynamics ; drug interation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary A possible interaction between the calcium antagonist nimodipine and the H2-receptor antagonists cimetidine and ranitidine has been investigated in two separate studies in healthy subjects. In eight young volunteers the concomitant administration of nimodipine 30 mg t.i.d. and cimetidine 1000 mg/d for 7 days led to a significant increase of the relative bioavailability of nimodipine. The changes in the pharmacokinetic parameters were not accompanied by discernible haemodynamic effects or any change in the tolerability of nimodipine. There was no evidence of any significant change in the steady-state pharmacokinetics of nimodipine during five days of combined treatment with 30 mg t.i.d. nimodipine and ranitidine 300 mg/d given as single morning dose to twelve healthy, elderly subjects. Analysis of haemodynamics, clinical chemistry and tolerance also did not reveal any difference between the two treatment periods.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1041
    Keywords: Nimodipine ; pharmacokinetics ; Chinese patients ; acute subarachnoid haemorrhage
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary Nimodipine pharmacokinetics was investigated in 12 Chinese patients with acute subarachnoid haemorrhage receiving an IV infusion of 1.6 or 2 mg/h (based on estimated body weight) for 10 days. Peripheral venous blood samples were collected for up to 4 days and plasma nimodipine was assayed by GC/ECD. The mean value was taken as the steady state concentration (Css) and Clearance (CL) (hourly dose/Css) was calculated. Eight survivors were given oral nimodipine (60 or 90 mg) every 6h (based on body weight), blood was sampled over 6 h and the plasma nimodipine level determined. The values for Css, CL and CL·kg−1 were 33.5 μg·l−1, 58 l·h−1 and 1.0 l·h−1·kg−1 respectively; in survivors receiving the drug orally, bioavailability of the 30 mg tablet was 9%. In one very sick patient given crushed tablets by naso-gastric tube, the AUC was very low; in vitro studies indicated that adsorption of nimodipine by the tubing was unlikely to have been the cause. The pharmacokinetic findings in Chinese patients are comparable to previously reported values in Caucasians.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-1041
    Keywords: Key words Cerivastatin; cytochrome P450 3A4 inhibition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Abstract Objective: Cerivastatin is a novel, synthetic, highly potent 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor that effectively reduces serum cholesterol levels at very low doses. It is exclusively cleared from humans via cytochrome P450-mediated biotransformation (demethylation M1; hydro‐xylation M23) and subsequent biliary/renal excretion of the metabolites. The influence of concomitant administration of erythromycin, a potent CYP3A4 inhibitor, on cerivastatin bioavailability and pharmacokinetics was investigated. Methods: Twelve healthy young male subjects received single oral doses of 300 μg cerivastatin alone or on the 4th day of a 4-day pre- and co-treatment with erythromycin 500 mg t.i.d. in a randomised, non-blind crossover study. Plasma and urine samples were analysed for cerivastatin and its major metabolites by validated specific high-performance liquid chromatography assays. Results: Cerivastatin was safe and well tolerated. No clinically relevant treatment-emergent changes in laboratory parameters were observed. The pre- and co-treatment with erythromycin 500 mg t.i.d. had a modest influence on cerivastatin clearance, leading to a mean increase in the maximum plasma concentration (Cmax) of 13% and a slightly increased terminal half-life (approximately 10%), resulting in a mean elevation of the area under the curve (AUC) of 21%; time to peak (tmax) remained unchanged. While the mean AUC of the metabolite M1 following the combined dosing was decreased by 60% compared with mono-dosing, the mean AUC of M23 exhibited an increase of approximately 60%. The respective Cmax results paralleled these pronounced effects, whereas the influence on mean terminal half-lives was small (i.e. for M23, an approximate 20% increase) or not observable (i.e. for M1). Conclusions: Concomitant administration of erythromycin 500 mg t.i.d. affects, to a certain extent, the metabolism of cerivastatin, administered as a single oral dose of 300 μg, resulting in a slightly increased exposure of the parent drug and active metabolites which, however, does not need dose adjustment. In addition, the small increase in cerivastatin half-life does not predict an accumulation beyond steady state. The pharmacokinetic data for the major metabolites suggest that the M1 metabolic pathway is more sensitive to CYP3A4 inhibition than the parallel M23 pathway, supporting recent in vitro findings that further cytochrome P450 isozymes are differently involved in the metabolic pathways of cerivastatin.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Fresenius' Zeitschrift für analytische Chemie 331 (1988), S. 359-366 
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary For the identification of UV spectra only such methods will be successful that incorporate all data of the whole spectrum because there is only a small content of information in UV spectroscopy. Numerical values based on integrated subsets of data are efficient for searching similar spectra. For identification three algorithms are described, the difference of two spectra after special normalization, the function of cross correlation and the rank of the two-row matrix containing the spectra of reference and sample. Difference and rank analysis have the advantage of taking the noise as precision of the system and using this as statistical defined limit for identification.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Chromatographia 23 (1987), S. 934-938 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Calibration ; Confidence interval ; Limit of determination ; Limit of calibration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary In HPLC calibration the expressions lowest calibration limit and determination limit are defined in statistical terms. The lowest calibration limit is the minimum mass in the measured series of calibration points. It is calculated from the confidence interval of the inverse of the calibration function as the lowest mass limit that may be differentiated from zero mass with a preset probability of error. If the calculated lowest calibration limit is lower than the actual data, points at lower concentration may be measured. The determination limit is the smallest concentration of an analysis that is differentiated from the concentration zero or an apparent blind value in the calibration curve with a given probability of error. Using two different UV-detectors (variable wavelength and photodiode-array) the lowest calibration limit is experimentally evaluated and compared with specific data for the detectors.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Chromatographia 25 (1988), S. 1039-1048 
    ISSN: 1612-1112
    Keywords: Coupled HPLC-UV/VIS ; Quantitative peak deconvolution ; Orthogonal polynomials ; Multicomponent analysis ; Photodiode array detection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Four different techniques to quantify unresolved chromatographic peaks with known spectral features combined with photodiode array detection, are investigated as regards their efficiency for the accurate and precise determination of drugs in the low μg-range. The comparison includes peak suppression utilising difference chromatograms, first-order derivative chromatograms, selective chromatograms, generated by the calculation of orthogonal polynomial shares, and the powerful least-squares multicomponent analysis approach. Each of these methods uses UV-spectra taken throughout, the peak. The results presented and conclusions reached should enable the chromatographer to come to a decision about the reasonable use of these options now provided by multichannel detection in HPLC.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1612-1112
    Keywords: HPLC/UV hyphenated techniques ; Principal component analysis ; eigenvalue ; Unresolved peaks ; peak purity (or peak homogeneity) ; Absorbance ratio
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Based on a thorough knowledge of the actual system precision significance testing of the primary eigen values, resulting from principal component analysis of the two-dimensional data array of HPLC with photodiode-array detection, is a powerful means to uncover unresolved chromatographic peaks. The implementation of this chemometric technique for assuring peak homogeneity and results showing the efficiency for two-component peaks in regard to spectral characteristics, chromatographic resolution and absorbance ratio of the investigated compounds are presented.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Fresenius' Zeitschrift für analytische Chemie 327 (1987), S. 794-797 
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Contrary to IR spectra there are only very few or no maxima in most UV spectra. Therefore library search based on peak tables will not be successful. The use of derivatives seems insufficient for there are too less data points for numerical derivatives and in case of trace analysis the signal-to-noise ratio is too bad. Integral numerical values are proposed as mean absorbance in selected wavelength ranges (200–400, 200–300, 200–260 nm) as characteristics for information ranges in the wavelength domaine. On the other hand, the absorbance domaine is characterized by the cross correlation of the spectrum in the same wavelength ranges. These numerical values will differentiate also very similar spectra as carbromal, ephedrin, pethidin, lidocain and atropin, showing only end absorptions up to about 240 nm.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Fresenius' Zeitschrift für analytische Chemie 331 (1988), S. 351-358 
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary For normalization of spectra in spectral libraries in UV/VIS range the maximum of absorbance, the area under the spectrum or a linear regression technique may be used. Using the error propagation law the best method should be the linear regression followed by area normalization. In practical work the area normalization has no advantages compared to a modified point normalization, where the mean of the maximum and the two next data points are taken. Therefore, in an automated comparison of UV spectra the modified point normalization is used for searching for similar spectra. The final comparison is done after linear regression normalization. This has advantages in calculation of error propagation and significance levels of two spectra. The reference spectrum is used as independent, the spectrum of the sample as dependent variable.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Fresenius' Zeitschrift für analytische Chemie 320 (1985), S. 671-672 
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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