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Biomedical subjects

A Hulshoff

Publications and source records attributed to A Hulshoff.

At least 19 recordsLinked to original sources
PubMed1987

Solid-phase extraction of vinblastine and vincristine from plasma and urine: variable drug recoveries due to non-reproducible column packings.

A sensitive and selective high-performance liquid chromatographic (HPLC) method for the determination of vinblastine and vincristine in plasma and urine is described. The drugs are isolated from 1.0 ml of the biological fluid with a solid-phase extraction column (Bond-Elut Diol). The HPLC method was combined with electrochemical detection at +850 mV versus an Ag/AgCl reference electrode. The detection limit is 100 pg for vinblastine and 250 pg for vincristine with a signal-to-noise ratio of 3, which permits the determination of these compounds in biological fluids at the nanogram level. Evaluation of the isolation method revealed that the drug recoveries and the reproducibility of the extraction procedure depend on the batch number of the solid-phase extraction column used.

Chromatography, High Pressure Liquid↗
PubMed1987

Pharmacokinetics of high-dose teniposide.

This paper describes the pharmacokinetics of teniposide (VM-26) after being administered iv in high doses to eight cancer patients (maximum dose, 1.0 g/m2). VM-26 levels in plasma, urine, saliva, duodenal fluid, and cerebrospinal fluid were determined using high-performance liquid chromatography in combination with electrochemical detection. The plasma concentration-time curve of VM-26 showed a triphasic decay with a slow third phase in five patients, whereas in two patients the plasma concentration decay was biphasic. The plasma pharmacokinetics of VM-26 proved to be linear and could be fitted to a three-compartment model (five patients) and to a two-compartment model (two). The steady-state volume of distribution varied from 13.2 to 24.7 L/m2. The total-body clearance ranged from 5.84 to 10.18 ml/minute/m2. Low concentrations of VM-26 were found in saliva, duodenal fluid, cerebrospinal fluid, and urine. Excretion of unchanged VM-26 into the urine varied from 8.8% to 13.9% of the administered dose. No glucuronide of VM-26 could be detected in plasma or other biological fluid.

Adult↗
PubMed1986

High-performance liquid chromatographic analysis of basic compounds on non-modified silica gel and aluminium oxide with aqueous solvent mixtures.

A comparison is made between the use of aluminium oxide and non-modified silica gel as cation-exchange materials for the separation of basic drugs (amines) with aqueous solvent mixtures. The retention behaviour of the amines is studied and appears to be controlled predominantly by the pH and the concentration and nature of the modifier; the nature and concentration of the competing ions and the buffer components of the mobile phase also exert some influence on the retention. Preparations with imidazoline and tetracycline derivatives have been analysed as examples of the application of these ion-exchange systems on non-modified silica gel and aluminium oxide in the analysis of pharmaceutical formulations.

Aluminum Oxide↗
PubMed1985

First-pass metabolism of pentamethylmelamine in the rat liver.

The disposition of pentamethylmelamine (PMM) was studied in the male Wistar rat. PMM (5 mg/kg) was administered intraarterially, i.v. (5 and 10 mg/kg), via the portal vein, and into the duodenum to cannulated and unanesthetized rats (n greater than or equal to 4) via infusion. Parent compound and metabolites were quantified by gas chromatography. The areas under the plasma concentration-time curves of PMM after intraarterial and i.v. administration were equal and twice as large as the areas after portal vein and intraduodenal administration. This indicated insignificant lung metabolism for PMM; the low bioavailability of PMM when given via the portal vein or intraduodenally (in both cases, some 50% of an i.v. dose) was the result of presystemic metabolism in the liver. PMM was completely absorbed after intraduodenal administration, and no intestinal metabolism was observed. Linear kinetic behavior of i.v. PMM was observed in the 5- to 10-mg/kg dose range. The area under the plasma concentration-time curve of the first metabolite N2,N2,N4,N6-tetramethylmelamine was significantly greater when PMM was given via the portal vein or intraduodenally than when given intraarterially or i.v. This indicated either extrahepatic elimination/renal excretion of PMM or the existence of an additional metabolic pathway. However, experiments with adrenalectomized rats and rats with ligated blood flow to the kidneys did not alter the area for the first metabolite. These findings may be explained by the formation of unknown metabolites and/or reactive intermediates of PMM.

Altretamine↗
PubMed1984

Rapid and selective derivatization method for the nitrogen-sensitive detection of carboxylic acids in biological fluids prior to gas chromatographic analysis.

A rapid and selective derivatization procedure is described for the pre-column labelling of carboxylic acids with a nitrogen-containing label. The carboxylic acid function is activated with 2-bromo-1-methylpyridinium iodide and the activated carboxylic acid function reacts with a primary or a secondary amine to yield an amide. With flurbiprofen as the test compound and dipropylamine as a label the acid was completely converted to the corresponding amide. The method was tested for several aliphatic, aromatic and for phenylacetic or phenylpropionic carboxylic acid derivatives, and was found to result in the complete derivatization of these compounds with a few exceptions only. The derivatization procedure is potentially useful for drug monitoring purposes, as is shown with the analysis of valproic acid and flurbiprofen in plasma.

Body Fluids↗
PubMed1984

Derivatization reactions in the gas-liquid chromatographic analysis of drugs in biological fluids.

Alkylation, acylation, silylation and other derivatization reactions applied to the gas chromatographic analysis of drugs in biological matrices are reviewed. Reaction conditions are discussed in relation to reaction mechanisms. Detector-oriented labelling of drugs, and derivatization with chiral reagents for the separation of enantiomers are surveyed. Data on the sample clean-up, derivatization and GLC analysis of more than 300 drugs and related compounds are listed.

Journal Article↗
PubMed1984

Cellular and subcellular studies of the biotransformation of hexamethylmelamine in rat isolated hepatocytes and intestinal epithelial cells.

The antitumor agent hexamethylmelamine is subject to oxidative metabolic conversion in rat isolated liver and small intestinal cells (conversion 40 times higher in hepatocytes). This N-demethylation is mediated by cytochrome P-450 in the microsomal fractions, and in mitochondrial preparations it has been found to occur via N- methylolpentamethylmelamine . Somehow, pentamethylmelamine, hydroxymethylpentamethylmelamine , or an intermediary metabolite becomes trapped in the intact cell, but the nature of the adduct formed is still unresolved. Pretreatment of rats with 3-methylcholanthrene p.o. caused a 5-fold increase in hexamethylmelamine turnover. Phorone administered in vivo prior to cell preparation (liver and gut) caused an increase in pentamethylmelamine production. The latter results together with results of adding glutathione to cell incubations demonstrate that glutathione contributes to the regulation of cytochrome P-450-mediated N-demethylation of hexamethylmelamine.

Altretamine↗
PubMed1983

Rapid formation of N-hydroxymethylpentamethylmelamine by mitochondria from rat small intestinal epithelium.

Isolated rat intestinal mitochondria showed a considerable capacity to convert hexamethylmelamine to its monodemethylated metabolite pentamethylmelamine. Mitochondrial turnover rate is about the same as compared with microsomal preparations. Only in mitochondrial incubations N-hydroxymethylpentamethylmelamine could be identified as a metabolic intermediate. The known chemical reactivity of carbinolamines means that this activation pathway in mitochondria could be involved in the pharmacological or toxic effects of hexamethylmelamine.

Altretamine↗
PubMed1983

Determination of amikacin in serum by high-performance liquid chromatography with ultraviolet detection.

A procedure for the determination of amikacin in serum is described. The aminoglycoside is extracted from serum by using a disposable cation-exchange column. The eluate of this column is derivatized with 1-fluoro-2,4-dinitrobenzene and subsequently analysed by reversed-phase high-performance liquid chromatography with ultraviolet detection at 365 nm. The absolute recovery of amikacin by this procedure is 72%. Kanamycin is used as the internal standard. The sensitivity is 1 mg/l for amikacin with samples of 200 microliters. Precision, expressed as the coefficient of variation, is about 3% in the therapeutic concentration range. The 2,4-dinitrophenyl derivative of amikacin is synthesized on a preparative scale by a new method and its structure is demonstrated to be the fully derivatized amikacin. The analysis of serum samples obtained in an in vivo experiment correlates well with the results from a microbiological assay.

Amikacin↗
PubMed1983

Analysis of creams. V. Application of thin layer chromatography. Part I.

A standard procedure, consisting of two TLC systems, for the qualitative control of creams is presented. All common cream excipients, except those of very high polarity, are separated in a simple gradient elution system, using diethyl ether as the eluent in a chromatographic chamber saturated with n-pentane. The very polar cream base components are separated using n-butanol-glacial acetic acid-water (20 + 2 + 5) as the eluent. The chromatographic behaviour of common cream excipients as well as three FNA cream bases and four commercial cream bases is discussed.

Chromatography, Thin Layer↗
PubMed1983

Analysis of creams. V. Application of thin layer chromatography. Part II.

A standard TLC procedure was tested for its applicability in the qualitative analysis of several creams. It was found that in creams of known composition the presence of almost all of the active cream components as well as the excipients can be confirmed. An additional eluent, spray reagent, or a liquid extraction clean-up step sometimes appeared to be necessary. If the cream base composition is not known, a 'fingerprint' of the various types of excipients is obtained with the described procedure.

Adrenal Cortex Hormones↗
PubMed1983

Analysis of creams. IV. Application of high performance liquid chromatography. Part I.

The possibilities of applying reversed-phase high performance liquid chromatography to the analysis of o/w emulsion type creams without preceding sample clean-up were investigated. The chromatographic behaviour of cream base components and active compounds in reversed phase systems consisting of methanol-water mixtures as the mobile phase and a chemically bonded octadecyl stationary phase, was studied. A number of active compounds and the preservative (sorbic acid) could be determined--often in one chromatographic run--without complications, by simply dissolving the sample in a suitable solvent mixture and injecting an aliquot of the solution into the chromatograph. Separation was achieved by the proper choice of methanol content, pH and ionic strength of the eluent. The compounds were detected by UV absorption. Some of the lipophilic cream base components could easily be determined in the same manner, with methanol as the eluent and with refraction index detection. The developed procedure was applied to the analysis of a number of creams. Some of the results are presented as examples, demonstrating the suitability of the method for quality control purposes.

Adrenal Cortex Hormones↗
PubMed1983

Gas chromatographic alkylation studies of phenytoin, mephenytoin and primidone: investigation of butylated derivatives.

The alkylation of phenytoin, mephenytoin and primidone with n-alkyl iodides in N,N-dimethylacetamide with tetramethylammonium hydroxide was investigated by gas chromatography. With methyl iodide phenytoin and mephenytoin were each converted into a single derivative; the use of other alkyl iodides yielded more than one product. Primidone was converted with methyl iodide and butyl iodide into a major derivative (> 90%) and a minor one. Butylation of the compounds by this method was compared with butylation in an acetone-butyl iodide mixture with potassium carbonate, caesium carbonate or silver oxide added, and with on-column butylation. All these methods resulted in the production of more than one derivative. The derivatives were identified by mass spectrometry and by 1H NMR and 13C NMR. With the acetone-butyl iodide-silver oxide method the main derivatives were O-butylated compounds. The other methods yielded predominantly N-butylated derivatives.

Journal Article↗
PubMed1983

The analytical control of the composition of creams.

The analysis without prior sample clean-up of promethazine hydrochloride or clioquinol in commercially available creams has been investigated using UV-spectrophotometry and titrimetric methods. The results were compared with those obtained by GLC and HPLC. Although in some cases the active drug could be determined satisfactorily using the comparatively non-selective UV-absorbance or titrimetric methods, these methods were found to be reliable only when applied to creams for which the qualitative and quantitative composition was completely known. Without prior sample clean-up, these methods will therefore be of interest mainly for process control purposes in manufacturing.

Journal Article↗
PubMed1983

Low oral bioavailability of hexamethylmelamine in the rat due to simultaneous hepatic and intestinal metabolism.

The disposition of both hexamethylmelamine (HMM) after intraarterial, i.v., portal vein, and intraduodenal administration and of pentamethylmelamine following its i.v. administration was studied in male Wistar rats. HMM (5 and 10 mg/kg) and pentamethylmelamine (5 mg/kg) were infused via implanted cannulas into conscious animals (n greater than or equal to 4). Plasma levels of parent compound and of metabolites were determined by gas chromatography. The areas under the plasma concentration-time curves of HMM following its intraarterial and i.v. administration were not significantly different, indicating that HMM was not appreciably metabolized in the lung. Areas under plasma-concentration-time curves of HMM following portal vein and intraduodenal administration were 27 and 8% of the area under the plasma concentration-time curve after i.v. administration, respectively. Absorption of HMM was complete as judged from metabolite data. The reduced bioavailability of HMM intraduodenally was thus a consequence of presystemic elimination in the liver and the gut wall. Extraction ratios (or first-pass effects) of the liver and the gut wall were 73 and 71%, respectively. Linear kinetic behavior of HMM i.v. was observed in the 5- to 10-mg/kg dose range. Extensive gut wall metabolism may have important implications for the antitumor activity mechanism of HMM.

Altretamine↗