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Biomedical subjects

U Jaehde

Publications and source records attributed to U Jaehde.

At least 37 records · Page 2Linked to original sources
PubMed1999

Utility of isotachophoresis-capillary zone electrophoresis, mass spectrometry and high-performance size-exclusion chromatography for monitoring of interleukin-6 dimer formation.

The utility of isotachophoresis-capillary zone electrophoresis (ITP-CZE) and high-performance size-exclusion chromatography (HPSEC) was investigated for determination of dimeric and monomeric recombinant human interleukin-6 (rhIL-6). Using ITP-CZE heterogeneity of dimeric rhIL-6 could be revealed resolving two peaks in the electropherograms, while with HPSEC dimeric rhIL-6 eluted as one homogeneous fraction. Both protein forms were monitored during incubation of monomeric rhIL-6 at different pH and temperature. The selectivity of counterflow ITP-CZE in conjunction with the low concentration determination limits enabled reanalysis of HPSEC fractions for identification of the dimer in the electropherograms. Both ITP-CZE and HPSEC were shown to be suitable to monitor the dimerization of rhIL-6, similar monomer-to-dimer peak area ratios were obtained throughout the incubation. Dimer formation kinetics increased with decreasing pH and with increasing temperature, it was entirely suppressed at neutral pH and room temperature. In contrast to HPSEC, ITP-CZE enabled separation of further still unidentified artifacts apparently formed during incubation of rhIL-6. CZE analysis in conjunction with electrospray ionization mass spectrometry revealed the non-covalent binding character of the dimeric rhIL-6 complex and facilitated interpretation of the electropherograms.

Chromatography, Gel↗
PubMed1999

Monitoring of chemotherapy-induced proteinuria using capillary zone electrophoresis.

Capillary zone electrophoresis (CZE) was investigated for its suitability to monitor proteinuria occurring during nephrotoxic drug therapy. Urine samples of tumor patients receiving chemotherapy consisting of carboplatin, etoposide, and ifosfamide were concentrated and desalted in microconcentrators and analyzed in two different alkaline CZE buffer systems. Reduction of electroosmotic flow (EOF) by the addition of putrescine increased the number of resolved protein peaks. Both CZE methods were linear between 2.5 and 50 microg/ml, exhibited satisfactory precision (relative standard deviation <10%) and were suitable for monitor the time course of proteinuria after chemotherapy administration. In contrast to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), CZE detected interindividual differences in protein patterns. Whereas these differences hampered a direct quantification of proteins in urine, they may contain information on the type or extent of kidney damage.

Adult↗
PubMed1999

Pharmacokinetic and pharmacodynamic comparison of two doses of calcium folinate combined with continuous fluorouracil infusion in patients with advanced colorectal cancer.

The optimum dose of calcium folinate (leucovorin) as modulator of fluorouracil has not been defined yet. We conducted a randomized trial to compare the pharmacokinetics/pharmacodynamics of two doses of calcium folinate. 16 patients with advanced colorectal cancer were treated with 650 mg/m2/d fluorouracil as 5 day continuous infusion and randomized to receive either 20 mg/m2 or 100 mg/m2 calcium folinate as short infusion twice daily. The two diastereoisomers of calcium folinate were analyzed separately by chiral HPLC to account for differences in their pharmacokinetics. The pharmacokinetics of fluorouracil was not affected by folinate dosing. Total clearance of the active (6S)-diastereoisomer was found to be lower after the higher dose of folinate which can be explained by nonlinear metabolism. The incidence of treatment-induced mucositis significantly increased with (6S)-folinate exposure, whereas fluorouracil exposure was not related to this type of toxicity. In conclusion, exposure to folinate is more important for toxicity in this regimen than fluorouracil pharmacokinetics. Therefore, monitoring of fluorouracil plasma levels is not useful in this combination. Our results show that folinate dose should be carefully selected. Lower doses of folinate might be preferred because of less toxicity compared to higher doses.

Aged↗
PubMed1999

Determination of platinum complexes in clinical samples by a rapid flameless atomic absorption spectrometry assay.

The frequent use of platinum (Pt) complexes in cancer chemotherapy and the application of new therapeutic options and dosing strategies have increased the need for rapid analytic procedures to determine Pt concentrations in the biologic fluids of patients. Therefore a flameless atomic absorption spectrometry method for the quantification of Pt in plasma and ultrafiltrate was developed and validated. A simple sample preparation of only one dilution step was established. Only 400 microL of whole blood was required for duplicate analysis of Pt in both matrices. The matrix-specific temperature programs took less than 75 seconds. The lower limit of quantification was 40 ng Pt/mL and 20 ng Pt/mL for plasma and ultrafiltrate, respectively. Suitable linearity could be reached using separate calibration curves for the high and low Pt concentration ranges. Recovery of Pt was complete, and there were no major stability problems. The accuracy and precision of the new method met the international criteria for the validation of bioanalytic methods. In addition, the use of different anticoagulants for clinical sampling, ultrafiltration systems, and ultrafiltration conditions were investigated. The assay has already been extensively applied to pharmacokinetic studies. In conclusion, the new Pt assay proved to be rapid, simple, sensitive, and suitable for clinical use.

Anticoagulants↗
PubMed1998

Quantitative trace analysis of interleukin-3, interleukin-6, and basic model proteins using isotachophoresis-capillary zone electrophoresis with hydrodynamic counterflow.

A quantitative analytical technique to determine trace concentrations of recombinant human interleukin-3 (rhIL-3), recombinant human IL-6 (rhIL-6), and various basic model proteins is described using isotachophoresis-capillary zone electrophoresis (ITP-CZE). Proteins were separated on coated fused-silica capillaries using a commercial capillary electrophoretic system modified for the application of isotachophoretic preconcentration with hydrodynamic counterflow. The effect of injection time and isotachophoretic focusing time was investigated and compared with predictions from existing mathematical models. Good linearity of the calibration graphs (r > 0.995) was observed for all investigated proteins. The limit of quantification was in the 10(-8) M range using UV detection at 200 nm. Within-day and between-day precision of peak area ranged between 1 and 6%. Precision was unaffected by isotachophoretic preconcentration. In conclusion, the described method is feasible to quantify trace concentrations of rhIL-3, rhIL-6, and basic proteins. Potential applications comprise issues of pharmaceutical quality control.

Electrophoresis, Capillary↗
PubMed1997

Determination of the cytotoxic catechol metabolite of etoposide (3'O-demethyletoposide) in human plasma by high-performance liquid chromatography.

The anticancer drug etoposide undergoes O-demethylation in humans. The formed catechol metabolite exhibits significant cytotoxic activity. A simple, rapid, selective, and sensitive reversed-phase high-performance liquid chromatography assay was developed for the measurement of etoposide catechol in plasma of tumour patients. The metabolite was quantified using electrochemical detection. Ascorbic acid was added to each sample to prevent oxidation of etoposide catechol during sample preparation. Linear responses were obtained between 40 ng/ml and 1.25 microg/ml with correlation coefficients exceeding 0.991. The detection limit was 10 ng/ml. Recovery, within-day precision, between-day precision and accuracy were satisfactory. The method has been applied to characterize the concentration-time profile of etoposide catechol in plasma of tumour patients following administration of high-dose etoposide.

Antineoplastic Agents, Phytogenic↗
PubMed1997

Five-day continuous infusion of 5-fluorouracil and pulsed folinic acid in patients with metastatic colorectal carcinoma: an effective second-line regimen.

OBJECTIVE: A previous phase I trial in 14 pretreated patients with progressive advanced colorectal cancer demonstrated 750 mg/m2 to be the maximum tolerable dose of 5-fluorouracil (5-FU) administered as a five-day continuous infusion modulated by short infusions of 100 mg/m2 folinic acid twice daily. The dose-limiting toxicities were hand-foot syndrome and severe mucositis. A response rate of 21% and 50% stable disease could be achieved. In order to determine the effectiveness and tolerability, we initiated a multicenter phase II trial applying a 650 mg/m2 recommended dose of 5-FU and 100 mg/m2 folinic acid twice daily every three weeks. PATIENTS AND METHODS: From January 1994 to July 1996, 88 advanced and progressive colorectal cancer patients either previously treated with a bolus schedule of 5-FU and folinic acid (34 patients) or without (54 patients) previous chemotherapy were included in this trial. RESULTS: In the group of previously treated patients, therapy led to 6% (2 of 34 patients) remissions while stable disease could be observed in 68% (23 of 34 patients) of the patients. The median survival time was 14 months. The main toxicity was mucositis grade 3 in 15% of the previously treated patients and 10% in the nonpretreated patients. In the population of nonpretreated patients, the overall response rate was 15% (eight of 54 patients) and stable disease could be induced in 67% (36 of 54 patients). The median survival time was 13.7 months. CONCLUSION: This regimen is an active second-line therapy in advanced colorectal cancer with minimal toxicity, thus preserving the quality of life during palliative chemotherapy. Antitumor activity in previously untreated patients does not seem superior to that obtained with weekly regimens applying 24- or 48-hour continuous infusions of 5-FU and folinic acid.

Adult↗
PubMed1996

Potential of on-line isotachophoresis-capillary zone electrophoresis with hydrodynamic counterflow in the analysis of various basic proteins and recombinant human interleukin-3.

Isotachophoresis-capillary zone electrophoresis with hydrodynamic counterflow was applied to the analysis of various basic model proteins and recombinant human interleukin-3. The use of coated capillaries and simple modifications of a commercial capillary zone electrophoresis (CZE) system allowed the detection of concentrations in the 10(-8) M region. The limit of detection was decreased by a factor of 100 compared to conventional CZE. The separation efficiency was unaffected by the preceding isotachophoretic step. Our method is applicable to the analysis of proteins with an isoelectric point higher than 7.0.

Buffers↗
PubMed1995

Effect of probenecid on the distribution and elimination of ciprofloxacin in humans.

OBJECTIVE: Probenecid-sensitive anion transport systems may be involved in distribution and elimination processes of anionic drugs. The aim of this study was to determine the effect of multiple probenecid treatment on the pharmacokinetic disposition of the zwitterionic fluoroquinolone ciprofloxacin in 12 healthy volunteers. METHODS: A single intravenous dose of 200 mg ciprofloxacin was given with and without multiple oral administration of probenecid in a randomized crossover fashion. Serial plasma, urine, saliva, tear, and sweat samples were drawn and analyzed for ciprofloxacin and its 2-aminoethylamino-metabolite (M1) by reversed-phase HPLC. RESULTS: Plasma area under the concentration-time curve and elimination half-life of ciprofloxacin were increased (p < 0.05), and urinary recovery and total and renal clearance decreased (p < 0.05) in the presence of probenecid. Nonrenal clearance and volume of distribution did not differ significantly with and without coadministration of probenecid. Peak plasma concentration, plasma area under the concentration-time curve, and elimination half-life of M1 were increased (p < 0.05) because of the higher amount of M1 formed and the reduced renal clearance (p < 0.05) of the metabolite. Saliva, tear, and sweat exposure were elevated (p < 0.05), but the alterations can be attributed primarily to the different kinetics of ciprofloxacin in plasma. CONCLUSIONS: Coadministration of probenecid altered the renal excretion and hence the plasma concentrations of ciprofloxacin. Metabolite kinetics and distribution into saliva, tears, and sweat were affected accordingly, but there was no direct effect of probenecid on these processes. This type of drug-drug interaction might be of clinical relevance when ciprofloxacin is combined with drugs eliminated by the organic anion transport system in the kidney tubules.

Adult↗
PubMed1995

Distribution kinetics of enoxacin and its metabolite oxoenoxacin in excretory fluids of healthy volunteers.

The distribution kinetics of enoxacin and its main metabolite oxoenoxacin in excretory fluids was investigated in 11 healthy volunteers. A single intravenous dose of 428 mg of enoxacin was given as a 1-h infusion. Serial samples of plasma, urine, saliva, nasal secretions, tears, and sweat were drawn and analyzed for enoxacin and oxoenoxacin by reversed-phase high-pressure liquid chromatography. Large differences in the concentration-time profiles of the excretory fluids analyzed were observed. Nasal secretions exhibited the highest enoxacin exposure, as assessed by the area under the concentration-time curve. Excretory fluid/plasma area under the concentration-time curve ratios were found to be 1.67 +/- 0.36 for nasal secretions, 0.76 +/- 0.28 for saliva, 0.25 +/- 0.07 for sweat, and 0.23 +/- 0.11 for tears. The elimination half-life of enoxacin from sweat (8.27 +/- 2.63 h) was significantly longer than that for plasma (5.10 +/- 0.46 h). Oxoenoxacin was detected in urine and saliva and exhibited a higher renal clearance and a lower saliva exposure than the parent compound. In contrast to that of the metabolite, distribution of enoxacin in saliva was found to be time and pH dependent. In conclusion, our study revealed considerable differences in the distribution kinetics of enoxacin among various excretory sites. Because of distinct acidic and basic properties, the anionic oxometabolite significantly differs from the zwitterionic parent compound in its distribution characteristics.

Adult↗
PubMed1995

Clinical pharmacokinetics in patients with burns.

Burn injury induces many different pathological changes in the human body, which potentially alter pharmacokinetic parameters such as bioavailability, protein binding, volume of distribution (Vd) and clearance. The extent of these alterations depends on the drug, the type and extent of injury and the time that elapsed between injury and drug administration. Bioavailability of large and hydrophilic molecules may be increased because of enhanced intestinal permeability. The free fraction of a drug in plasma can be increased (when primarily bound to albumin) or decreased (when primarily bound to alpha 1-acid glycoprotein). Vd may change as a consequence of altered protein binding or an enlarged extracellular fluid volume. Alterations in clearance may be due to changes in glomerular filtration, tubular secretion, hepatic blood flow, drug-metabolising activity, protein binding and to the presence of additional elimination pathways. Elimination half-life changes when Vd and/or clearance is affected following burn injury. The therapeutic consequences of pharmacokinetic alterations are discussed in principle, and for specific treatment with antibacterials, anti-ulcer drugs, analgesics, muscle relaxants, anxiolytics, phenytoin and cyclosporin. If significant changes in pharmacokinetic disposition occur following thermal injury, therapeutic drug monitoring and dosage adjustment may be required to ensure rational and well tolerated drug therapy in patients with burns. Future studies should focus on the impact of specific patient variables (e.g. type of injury and size of burn) on the extent of pharmacokinetic alterations.

Absorption↗
PubMed1994

Quantification and visualization of the transport of octreotide, a somatostatin analogue, across monolayers of cerebrovascular endothelial cells.

Confocal laser scanning microscopy (CLSM) was used to quantify and visualize the transport of the octapeptide and somatostatin analogue, octreotide (SMS 201-995, Sandostatin), across monolayers of bovine cerebrovascular endothelial cells, an in vitro model of the blood-brain barrier. The concentrations of octreotide and its conjugates in the cell culture medium were determined by radioimmunoassay (RIA). Two fluorescent conjugates of octreotide (FITC- and NBD-octreotide) were used to obtain CLSM images. The peptides did not undergo significant degradation in the presence of brain endothelial cell monolayers. The transport rate of octreotide expressed as clearance (Cl) and endothelial permeability (Pe) did not depend on either the initial concentration (between 10 nM and 1 microM) or the site of administration (luminal or abluminal side of the monolayer), indicating the absence of saturable and/or asymmetrical transport mechanisms. The Pe of octreotide and that of the paracellular permeability marker fluorescein correlated well. Although the conjugates are more lipophilic than octreotide itself, they exhibited lower Cl and Pe, values probably because of their larger molecular size. On the CLSM images, FITC-octreotide was present only in the intercellular space, while the cells did not exhibit detectable fluorescence. Transport studies and CLSM images suggest that octreotide passes the endothelial monolayer primarily via the paracellular route without significant contribution of carrier-mediated transport.

4-Chloro-7-nitrobenzofurazan↗
PubMed1994

In vitro and in vivo transport of zidovudine (AZT) across the blood-brain barrier and the effect of transport inhibitors.

The transport of the antiviral nucleoside analogue zidovudine (3'-azido-3'-deoxythymidine; AZT) into the central nervous system (CNS) was characterized in vitro and in vivo. The in vitro model consisted of primary cultures of isolated bovine capillary endothelial cells. The transport rate of AZT across the monolayer, expressed as endothelial permeability P, was determined following luminal and abluminal administration. P did not differ between the two administration sites (luminal, 1.65 +/- 0.44 cm/min/10(3); abluminal, 1.63 +/- 0.28 cm/min/10(3)). The transport of AZT across the endothelial cell monolayer was found to be concentration independent in the range between 0.4 and 50 micrograms/mL. AZT transport was not affected by pretreatment of the cells with either metabolic inhibitors (DODG and DODG/NaN3) or probenecid. This suggests that AZT passes the monolayer mainly by passive diffusion. The in vivo transport of AZT across the blood-brain barrier and the blood-CSF barrier was studied in male Wistar rats after coadministration of potential inhibitors of active transport of AZT: probenecid (organic anion transport) and thymidine (nucleoside transport). Intracerebroventricular and intravenous coadministration of probenecid caused a significant (P < 0.001) increase in the CSF/plasma concentration ratio compared to the control phase, indicating that the organic anion carrier is involved in AZT transport from CSF to blood. Since there was no effect of probenecid on the transport of AZT in vitro, it is suggested that this carrier is located at the choroid plexus. Coadministration of thymidine did not affect the CSF/plasma concentration ratio, suggesting that a nucleoside carrier system is not involved in AZT transport into or out of the CNS.

Analysis of Variance↗
PubMed1994

Effect of an antacid containing magnesium and aluminum on absorption, metabolism, and mechanism of renal elimination of pefloxacin in humans.

The effects of an antacid containing magnesium and aluminum hydroxide on the pharmacokinetics of pefloxacin in 10 healthy volunteers were investigated. In a randomized crossover design, each subject received an oral dose of 400 mg of pefloxacin either with or without multiple doses of the antacid. The concentrations of pefloxacin and its metabolites in plasma and urine were determined by high-performance liquid chromatography assays. We found that coadministration of magnesium and aluminum hydroxide caused a decrease of levels of pefloxacin in plasma and urine. The area under the plasma concentration-time curve decreased significantly (P < 0.001), suggesting impaired absorption of pefloxacin from the gastrointestinal tract. The relative bioavailability of pefloxacin after the antacid treatment was 44.4% +/- 23.8%, compared with that after a single administration. The underlying mechanism of this drug interaction is the formation of chelate complexes and probably also physical adsorption to the aluminum hydroxide gel. The metabolism of pefloxacin was not altered by the antacid treatment. Renal clearance was found to depend on urinary pH. Terminal half-life was significantly shorter after the antacid treatment, probably because of an increase in nonrenal clearance. In conclusion, pefloxacin should be given at least 2 h before the antacid to ensure sufficient therapeutic efficacy of the quinolone.

Adult↗