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Biomedical subjects

R W Sparidans

Publications and source records attributed to R W Sparidans.

At least 19 recordsLinked to original sources
PubMed2006

Development and validation of a quantitative assay for the measurement of two HIV-fusion inhibitors, enfuvirtide and tifuvirtide, and one metabolite of enfuvirtide (M-20) in human plasma by liquid chromatography-tandem mass spectrometry.

A method for the quantification of two peptide HIV-1 fusion inhibitors (enfuvirtide, T-20 and tifuvirtide, T-1249) and one metabolite of enfuvirtide (M-20) in human plasma has been developed and validated, using liquid chromatography coupled with electrospray tandem mass spectrometry (LC-MS/MS). The analytes were extracted from plasma by solid-phase extraction (SPE) on vinyl-copolymer cartridges. Chromatographic separation of the peptides was performed on a Symmetry 300 C(18) column (50mmx2.1mm I.D., particle size 3.5 microm), using a water-acetonitrile gradient containing 0.25% (v/v) formic acid. The triple quadrupole mass spectrometer was operated in the positive ion-mode and multiple reaction monitoring (MRM) was used for peak detection. Deuterated (d60) enfuvirtide and (d50) tifuvirtide were used as internal standards. The assay was linear over a concentration range of 20-10,000 ng/ml for enfuvirtide and tifuvirtide and of 20-2000 ng/ml for M-20. Intra- and inter-assay precisions and deviations from the nominal concentrations were </=13%. Stability of the analytes was tested under all relevant conditions for sample handling. The method was capable to measure concentrations of enfuvirtide and its metabolite in plasma samples of human immunodeficiency virus type-1 (HIV-1) infected patients treated with the drug.

Enfuvirtide↗
PubMed2006

Isolated lung perfusion with melphalan: pharmacokinetics and toxicity in a pig model.

BACKGROUND: In patients with unresectable lung cancer or pulmonary metastases, isolated lung perfusion (ILP) has been described as an alternative method to deliver high-dose chemotherapy to the lungs, thereby minimizing systemic toxicity. Pharmacokinetics of ILP have not been extensively investigated. Therefore, we studied the feasibility of ILP with melphalan in a pig model with emphasis on pharmacokinetics and acute lung damage. METHODS: Five pigs underwent ILP with melphalan. Blood and tissue samples were obtained for determination of melphalan levels. Tissue biopsies were taken for microscopic evaluation of lung damage. RESULTS: During ILP, no hemodynamic effects of importance were noted. No systemic leakage of melphalan was observed in any of the animals. Compared with normal lung tissue, microscopic examination of lung tissue after perfusion without melphalan showed pulmonary edema. Directly after melphalan perfusion additional hemorrhagic areas were seen; however, electron microscopy displayed no irreversible endothelial damage. CONCLUSION: This study on pigs proved to be a well reproducible model for ILP with melphalan. Pharmacokinetics show a safety profile with no systemic toxicity, which could justify further patient studies, necessary to determine its effect on pulmonary metastases in humans, especially in case of adjuvant therapy after surgical resection or in unresectable disease.

Animals↗
PubMed2005

Phase I and pharmacological study of the farnesyltransferase inhibitor tipifarnib (Zarnestra, R115777) in combination with gemcitabine and cisplatin in patients with advanced solid tumours.

This phase I trial was designed to determine the safety and maximum tolerated dose (MTD) of tipifarnib in combination with gemcitabine and cisplatin in patients with advanced solid tumours. Furthermore, the pharmacokinetics of each of these agents was evaluated. Patients were treated with tipifarnib b.i.d. on days 1-7 of each 21-day cycle. In addition, gemcitabine was given as a 30-min i.v. infusion on days 1 and 8 and cisplatin as a 3-h i.v. infusion on day 1. An interpatient dose-escalation scheme was used. Pharmacokinetics was determined in plasma and white blood cells. In total, 31 patients were included at five dose levels. Dose-limiting toxicities (DLTs) consisted of thrombocytopenia grade 4, neutropenia grade 4, febrile neutropenia grade 4, electrolyte imbalance grade 3, fatigue grade 3 and decreased hearing grade 2. The MTD was tipifarnib 200 mg b.i.d., gemcitabine 1000 mg m(-2) and cisplatin 75 mg m(-2). Eight patients had a confirmed partial response and 12 patients stable disease. No clinically relevant pharmacokinetic interactions were observed. Tipifarnib can be administered safely at 200 mg b.i.d. in combination with gemcitabine 1000 mg m(-2) and cisplatin 75 mg m(-2). This combination showed evidence of antitumour activity and warrants further evaluation in a phase II setting.

Administration, Oral↗
PubMed2001

Degradation kinetics of aplidine, a new marine antitumoural cyclic peptide, in aqueous solution.

The degradation kinetics of aplidine were investigated using reversed-phase high-performance liquid chromatography combined with UV detection. Aplidine consists of at least two isomers that undergo interconversion at a low rate. Influences of pH, temperature, buffer ions and ionic strength on the degradation kinetics were studied. The log kobs) -pH profile can be divided into three parts, a proton, a solvent and a hydroxyl-catalysed section. The stability-indicating properties of the used analysis technique as well as the identities of the main degradation products were checked using gradient liquid chromatography and mass spectrometric detection. The overall degradation rate constant as a function of the temperature under acidic and alkaline conditions obeys the Arrhenius equation. No catalytic influences were observed with phosphate and carbonate buffers and, in addition, the ionic strength showed no substantial effect on the stability, as expected. Results from gradient LC-MS indicated that hydrolysis of the ester groups present in the ring structure was the main degradation route. There is no difference in degradation rate constants for the individual isomers.

Antineoplastic Agents↗
PubMed2001

Liquid chromatographic assay for simultaneous determination of abacavir and mycophenolic acid in human plasma using dual spectrophotometric detection.

A combined bio-analytical assay for abacavir, a reversed transcriptase inhibitor, and mycophenolic acid (MPA), based on reversed-phase liquid chromatography and both ultraviolet (UV) absorption and fluorescence detection, is reported. Both analytes are extracted from plasma with acetonitrile. After centrifugation, evaporation of the supernatant and reconstitution in water, the sample is injected into the chromatograph. Abacavir is detected using UV detection at 285 nm and MPA spectrofluorometrically at 345 and 430 nm for excitation and emission, respectively. The method has been validated in the 80-2000 ng/ml range for abacavir and in the 10-10,000 ng/ml range for MPA for 200-microl plasma samples. The lower limits of quantification are 80 and 10 ng/ml for abacavir and MPA, respectively. Precisions and accuracies are < or = 8% in the valid concentration ranges of both analytes.

Anti-HIV Agents↗
PubMed2001

Chemical and enzymatic stability of a cyclic depsipeptide, the novel, marine-derived, anti-cancer agent kahalalide F.

Kahalalide F is a cyclic depsipeptide isolated from the Hawaiian mollusk Elysia rufescens. This compound is under present phase I clinical investigations as an anti-tumor drug. The role of possible metabolic reactions of this drug in (pre-)clinical investigations has not yet been explored. The first results for kahalalide F in this field of research are given in this paper. The chemical degradation of kahalalide F was investigated under acid, neutral and alkaline conditions using high-performance liquid chromatography with ultraviolet detection. The half-lives at 80 degrees C were 1.1, 20 and 8.6 h at pH 0, 1 and 7, respectively. At 26 degrees C and pH 11, the half-life was 1.65 h. At pH 7 and 11, only one reaction product of kahalalide F was observed, kahalalide G, the hydrolyzed lactone product of kahalalide F. At pH 0 and 1, additional reaction products emerged. Metabolic conversion of kahalalide F was tested in vitro using three different enzyme systems based on pooled human microsomes, pooled human plasma and uridine 5'-diphosphoglucuronyl transferase, respectively. The incubated samples were analyzed using the same chromatographic technique as for the degradation samples. Biotransformations were not observed under these conditions and, therefore, it is concluded that kahalalide F is a metabolically stable drug.

Antineoplastic Agents↗
PubMed2001

Search for metabolites of ecteinascidin 743, a novel, marine-derived, anti-cancer agent, in man.

Ecteinascidin 743 (ET-743) is a potent anti-tumoral agent of a marine origin. It is currently being tested in phase II clinical trials using a 3-weekly 24-h i.v. infusion of 1500 microg/m(2) and 3-h infusions of 1650 microg/m(2). Knowledge of the metabolism of ET-743 is, however, still scarce. In the present study, a qualitative chromatographic discovery of metabolites of ET-743 in man is reported. ET-743 and its demethylated analog ET-729 were incubated at 37 degrees C in the presence of enzyme systems, pooled human microsomes, pooled human plasma and uridine 5'-diphosphoglucuronyltransferase, respectively, in appropriate media. Reaction products were investigated chromatographically using photodiode array and ion spray-mass spectrometric detection (LC-MS). The main reaction products in microsomal incubations of ET-743 resulted from a remarkable breakdown of the molecule. In plasma the drugs were deacetylated, and the transferase did actually yield a glucuronide of both ET-743 and ET-729. In contrast, screening of urine, plasma and bile, collected from patients treated with ET-743 at the highest dose levels, using a sensitive LC-MS assay, did not result in detection of ET-729 and metabolites which were generated in vitro. The urinary excretion of ET-743 in man was lower than 0.7% of the administered dose for a 24-h infusion.

Antineoplastic Agents, Alkylating↗
PubMed2000

Sensitive liquid chromatographic assay for amprenavir, a human immunodeficiency virus protease inhibitor, in human plasma, cerebrospinal fluid and semen.

A sensitive bio-analytical assay for amprenavir, a human immunodeficiency virus protease inhibitor, based on reversed-phase liquid chromatography and fluorescence detection, is reported. The analyte is extracted from the matrix, plasma, cerebrospinal fluid (CSF) or semen, with chloroform using propyl-p-hydroxybenzoate as an internal standard. After centrifugation, evaporation of the organic phase and reconstitution in the eluent, the sample is injected into the chromatograph. The analyte is detected spectrofluorometrically at 270 and 340 nm for excitation and emission, respectively. The method has been validated in the 1-1000 ng/ml range for a 50-microl volume of plasma and in the 0.5-50 ng/ml range for a 100-microl volume of CSF and semen. The lower limit of quantification was 0.5 ng/ml in CSF and 1 ng/ml in both plasma and semen. Precision and accuracy both meet the current requirements for a bio-analytical assay and are <15% in the validated ranges. The assay was successfully used to obtain a concentration-time curve of amprenavir in plasma.

Adult↗
PubMed2000

Semi-automatic liquid chromatographic analysis of olpadronate in urine and serum using derivatization with (9-fluorenylmethyl)chloroformate.

The semi-automatic bioanalytical assays for olpadronate [(3-dimethylamino-1-hydroxypropylidene)bisphosphonate] involves a protein precipitation with trichloroacetic acid and a double co-precipitation with calcium phosphate for serum samples and a triple calcium co-precipitation for urine samples. These manual procedures are followed by an automated solid-phase extraction on a cation-exchange phase. The procedure is continued either directly, at high olpadronate levels in urine, or after off-line evaporation under nitrogen and reconstitution in water on the same robotic workstation. The continued automatic procedure comprehends derivatization with (9-fluorenylmethyl)chloroformate, ion-pair liquid-liquid extraction and ion-pair HPLC with fluorescence detection at 274/307 nm. The intra- and inter-day precisions for urine and serum samples are typically in the 5-8% range for different olpadronate concentrations [levels near the lower limit of quantification (LLQ) excluded]. The LLQ is 5 ng/ml olpadronate for a 2.5-ml urine sample and 10 ng/ml for a 1-ml serum sample, respectively.

Automation↗
PubMed1999

Improved and simplified liquid chromatographic assay for adefovir, a novel antiviral drug, in human plasma using derivatization with chloroacetaldehyde.

A rapid and simplified chromatographic assay is reported for the quantification of adefovir (PMEA) utilizing derivatization with chloroacetaldehyde. Adefovir is isolated from plasma using protein precipitation with trichloroacetic acid; next, the fluorescent 1,N6-etheno derivative is directly formed at 98 degrees C in the buffered extract with chloroacetaldehyde. This derivative is analyzed using isocratic ion-pair liquid chromatography and fluorescence detection at 254 nm for excitation and 425 nm for emission. In the evaluated concentration range (10-1000 ng/ml) precisions < or = 5% and accuracies between 95 and 117% were found, using a 0.2-ml volume of plasma. The lower limit of quantification is 10 ng/ml with a intra-assay precision of 16%. The currently reported bioanalytical method is 20-25-fold more sensitive than previously published assays.

Acetaldehyde↗
PubMed1999

Quantitative determination of abacavir (1592U89), a novel nucleoside reverse transcriptase inhibitor, in human plasma using isocratic reversed-phase high-performance liquid chromatography with ultraviolet detection.

Abacavir is a novel nucleoside reverse transcriptase inhibitor for the treatment of HIV-1 infection. A simple and rapid high-performance liquid chromatographic method for the quantification of abacavir in human plasma suitable for pharmacokinetic research purposes is described. Sample pretreatment consists of protein precipitation with perchloric acid. The supernatant is injected directly into the chromatographic system after centrifugation. The drug is separated from endogenous compounds by isocratic reversed-phase high-performance liquid chromatography with ultraviolet detection at 285 nm. The method has been validated over the range of 20-2000 ng/ml using a volume of 300 microl of plasma. The assay is linear over this concentration range as indicated by the F-test for lack-of-fit. Within- and between-day precisions are less than 7.5% for all quality control samples. The lower limit of quantitation is 20 ng/ml and the recovery of abacavir is 88.1% (+/-1.3%). Frequently coadministered drugs did not interfere with the described methodology. Abacavir is stable in human plasma under various relevant storage conditions, for example when stored for 51 days at -20 degrees C. This validated assay is suited for use in pharmacokinetic studies with abacavir in human plasma and can readily be implemented in the setting of a hospital laboratory for the monitoring of abacavir concentrations.

Acquired Immunodeficiency Syndrome↗
PubMed1999

Bioanalysis of m-iodobenzylguanidine in plasma by high-performance liquid chromatography after derivatization with benzoin.

A sensitive chromatographic assay has been developed for m-iodobenzylguanidine (MIBG) in human plasma based on the derivatization with benzoin. MIBG is first isolated from plasma using solid-phase extraction on a cyanopropyl-modified silica phase. After evaporation of the eluate, a fluorescent derivative is formed using benzoin. The derivative is analysed by reversed-phase liquid chromatography using a mixture 60% (v/v) acetonitrile, 30% (v/v) water and 10% (v/v) of the 0.5 M Tris buffer (pH 8.0) as the eluent and fluorescence detection at 320 nm for excitation and 435 nm for emission, respectively. In the evaluated concentration range (2-200 ng/ml) precisions < or = 10% and accuracies in between 90 and 100% have been found, with 2 ng/ml being the lower limit of quantification using a 0.5-ml plasma sample volume. The assay can also be used without the internal standard benzylguanidine. The assay was successfully used to obtain a pharmacokinetic curve of MIBG.

3-Iodobenzylguanidine↗
PubMed1999

Semi-automatic liquid chromatographic analysis of pamidronate in urine after derivatization with 1-naphthylisothiocyanate.

An existing sensitive chromatographic assay for pamidronate in urine has considerably been automated. Using the same sample processor, the solid-phase extraction (SPE) was automated separately from the derivatization with 1-naphthylisothiocyanate, the two-fold ion-pair liquid-liquid-extraction and the treatment with hydrogen peroxide for the 2-20 ng/ml concentration range. The automatic procedure was preceded by a triple calcium precipitation and interrupted by evaporation of the SPE eluate under nitrogen. For the 0.5-5 microg/ml concentration range one automatic sequence was used by avoiding evaporation during the sample treatment. In addition to the labour-saving of the semi-automatic procedure, the daily sample-throughput was improved compared to the existing manual assay. Further, the validation showed marginal improvements in the precision, accuracy and lower limit of quantification.

1-Naphthylisothiocyanate↗
PubMed1999

Bioanalysis of aplidine, a new marine antitumoral depsipeptide, in plasma by high-performance liquid chromatography after derivatization with trans-4-hydrazino-2-stilbazole.

A sensitive bio-analytical assay in plasma of the depsipeptide aplidine is reported, based on reversed-phase liquid chromatography and fluorescence detection of the trans-4'-hydrazino-2-stilbazole (4'H2S) derivative of the analyte. At ambient temperature, two conformations of the depsipeptide are observed in solution due to cis-trans isomerism at the proline-pyruvoyl peptide bond. Aplidine is isolated from the matrix by solid-phase extraction on an octadecyl modified silica stationary phase. After evaporation of the acetone eluate, a derivatization with 4'H2S is performed in a water-acetonitrile mixture at pH 4. The reaction mixture is injected directly into the chromatograph and the analyte is quantified by fluorescence detection at 410 and 560 nm for excitation and emission, respectively. The method has been validated in the 2-100 ng/ml-range, 2 ng/ml being the lower limit of quantification. Precision and accuracy both meet the current requirements for a bioanalytical assay. The identity of the 4'H2S reaction products of aplidine have been confirmed by mass spectrometric analysis. Finally, the method has been employed for a pilot pharmacokinetic study of aplidine in mice which demonstrated its usefulness for pharmacological research.

Animals↗
PubMed1999

Bioanalysis of thiocoraline, a new marine antitumoral depsipeptide, in plasma by high-performance liquid chromatography and fluorescence detection.

A sensitive bioanalytical assay for thicoraline, an investigational marine anticancer agent, in plasma, based on reversed-phase liquid chromatography and fluorescence detection, is reported. The proteins in the sample are precipitated by the addition of acetonitrile. After centrifugation, the supernatant is injected directly into the chromatograph. The analyte is quantified by fluorescence detection with excitation and emission at 365 and 540 nm, respectively. The method has been validated in the 1-100 ng/ml range, 1 ng/ml being the lower limit of quantification. Precision and accuracy both meet the current requirements for a bio-analytical assay and are <15% at 1 ng/ml and < or =5% in the 5-100 ng/ml range. Plasma samples can be stored for at least 4 months at -80 degrees C. Finally, the usefulness of this method for pharmacological research was shown in a pilot study of the pharmacokinetics of thiocoraline in rats.

Animals↗
PubMed1999

Chromatographic analysis of bisphosphonates.

Chromatographic analysis of bisphosphonates in the past has been based primarily on reversed-phase liquid chromatography (RPLC) and ion-exchange chromatography. Gas chromatography (GC) and recently even capillary electrophoresis have also been employed. For bioanalysis, pre-treatment of the sample is a major part of the analysis; protein precipitation, calcium precipitation, solid-phase extraction (SPE) and derivatization have demonstrated to play an important role in bisphosphonate assays. For some of these treatments, for example SPE and derivatization, automation may be possible. Derivatization is a prerequisite for GC analysis of bisphosphonates; a volatile derivative has to be formed. For liquid chromatography, two types of derivatization are known for bisphosphonates. First, the bisphosphonate side chain can be modified by a chemical reaction to yield a derivative with advantageous chromatographic and spectroscopic properties. Secondly, by complexation of both phosphonate groups or of phosphate after decomposition of the analyte, a coloured complex can be formed. The most sensitive bioanalytical methods are based on RPLC and fluorescence detection, if necessary after derivatization. If low detection limits are not required, for example for analysis of pharmaceutical preparations, non-specific detection methods can be applied.

Animals↗
PubMed1998

Semi-automatic liquid chromatographic analysis of pamidronate in serum and citrate plasma after derivatization with 1-naphthylisothiocyanate.

The semi-automatic method for the determination of the bisphosphonate pamidronate in serum and citrate plasma involves a manual protein precipitation with trichloroacetic acid and a manual coprecipitation of the bisphosphonate with calcium phosphate, followed by an automated solid-phase extraction on anion-exchange columns. After off-line evaporation of the extract under nitrogen and reconstitution in water, the automatic procedure is continued by automatic derivatization with 1-naphthylisothiocyanate, ion-pair liquid-liquid extraction and a treatment with hydrogen peroxide, prior to analysis by ion-pair HPLC and fluorescence detection at 285/390 nm. The intra- and inter-day precisions are 1.3 and 7%, respectively, for a standard of 100 ng ml(-1) pamidronate in serum; the average accuracy for this standard is 107%. The lower limit of quantification is 20 ng ml(-1) pamidronate in 1 ml of human serum.

1-Naphthylisothiocyanate↗