Je Greving

DETERMINATION OF CARBOXYLIC-ACIDS IN PICOMOLE RANGE AFTER DERIVATIZATION WITH PENTAFLUOROBENZYL BROMIDE AND ELECTRON-CAPTURE GAS-CHROMATOGRAPHY

Abstract A method is presented for the determination of picomole quantities of carboxylic acids by gas chromatography in combination with electron capture detection. The acids are extracted from aqueous media into dichloromethane by ion-pair extraction with tetrapentylammonium ions, and derivatized as their pentafluorobenzyl esters. These derivatives have good chomatographic properties with minimum detectable amounts of ca . 0.15 pg 250 pg or greater quantities of the acids can be used. Recoveries are ca . 90% with a precision of ca . 6% at the 10-ng level.

Disposition and clinical pharmacokinetics of microcrystalline theophylline.

SummaryVariation in the systemic disposition of theophylline after ingestion of a new microcrystalline product (Theolair®) has been investigated in 7 hospitalized patients with generalized obstructive lung disease. Disposition (absolute bioavailability) was determined by comparing in the same patients the areas under the serum concentration-time curves after a single oral dose of microcrystalline theophylline and after an intravenous infusion of aminophylline. Oral absorption appeared to be fast. The half-life of absorption was 19±9 min (mean±SD). Maximal serum concentrations reached after 100±30 min were found to be in a rather narrow range: 9.8±2.5 mg · 1−1. The absolute bioavailability of the microcrystalline preparation was high and it showed only small variation: 102.7±10.2% of the dose. Relevant pharmacokinetic parameters (half-life of elimination, volume of distribution and total body clearance) were determined after both routes of administration. Individual dosage regimens required to obtain a therapeutic serum concentration were calculated for each individual patient on the basis of the observed pharmacokinetic parameters.

CORRELATION OF SERUM AND SALIVA THEOPHYLLINE CONCENTRATIONS AFTER ADMINISTRATION OF A SUSTAINED-RELEASE PREPARATION

SummaryThe correlation between serum and saliva levels of theophylline was investigated in seven healthy volunteers after multiple dose administration of a low dose (300 mg/day) and a high dose (900 mg/day) of a sustained release theophylline preparation (Theo-Dur®). Tablets were taken for five days, at 8 a.m. and 8 p.m. and a last dose was taken on Day 6 at 8 a. m. Fourteen serum and saliva samples were collected simultaneously during the dosing period and for up to 32 h after the last dose. On the 300 mg/day regimen the level in saliva was 55.3% of the serum level, with an overall variability of 6.7% and an intrasubject variability of 10.5%. After 900 mg/day, the saliva concentration was 55.5% of the serum concentration, with an overall variability of 7.6% and an intrasubject variability of 12.7%. A good correlation was found between both determinations (r=0.99), which suggests that saliva levels could be used to monitor theophylline after administration of a sustained release tablet.

ANALYSIS OF QUATERNARY AMMONIUM-COMPOUNDS BY ION-PAIR THIN-LAYER CHROMATOGRAPHY ON SILICA-GEL

Abstract A general approach to the chromatographic analysis of quaternary ammonium compounds on silica gel thin layers is described. The quaternary cations migrate as ion pairs with bromide or iodide as counter ions. Methanol or chloroform-methanol mixtures serve as developing solvents, in which excess amounts of NaBr or NaI are dissolved. If the solvent cannot dissolve sufficient quantities of halide salts, the latter can be sprayed onto the plate as a methanol solution prior to development. The separation patterns of the quaternary ammonium compounds can be influenced by the choice of counter ion and by the choice of the organic solvent components.

DETERMINATION OF OXYPHENONIUM BROMIDE IN PLASMA AND URINE BY MEANS OF ION-PAIR EXTRACTION, DERIVATIZATION AND GAS CHROMATOGRAPHY-ELECTRON-CAPTURE DETECTION

A sensitive and selective method for the determination of the quaternary ammonium compound oxyphenonium bromide (Antrenyl), a drug with strong anticholinergic properties, in human plasma and urine is described. The method is based on ion-pair extraction of the cation with perchlorate, a re-extraction according to ion-pair principles with tetrapentylammonium as the counter ion, hydrolysis to cyclohexylphenylglycolic acid, derivatization of this acid to its pentafluorobenzyl ester and determination of the ester by gas chromatography and electron-capture detection. Quantitation is possible down to 2 ng/ml of oxyphenonium bromide using 1 ml of plasma and down to 200 ng/ml using 0.1 ml of urine. The method described can also be applied to other anticholinergic drugs with an ester function.

Identification of Ergot-peptide alkaloids, based on gas—liquid chromatography of the peptide moiety

Abstract A simple and rapid method for the identification of ergot-peptide alkaloids is described. At temperatures around 300° instantaneous degrations of the free alkaloids occurs in the injection port of the gas chromatograph, each alkaloid yielding a specific set of peptide degradation products, which are subsequently separated on a SE-30 column. Since the lysergic acid moiety cannot be seen in the gas chromatogram, the separation of alkaloids which differ in that part of the molecule is not possible and should be done by thin-layer chromatography or high-performance liquid chromatography. However, combination of these two techniques with the present method provides an excellent identification of all of the possible ergot-peptide alkaloids, including stereoisomers.

ION-PAIR ADSORPTION CHROMATOGRAPHY OF BASIC DRUGS USING STRAIGHT-PHASE SYSTEMS ON SILICA-GEL THIN-LAYERS

Abstract A general approach to the ion-pair adsoption chromatography of basic drugs on silica gel thin layers is described. Under acidic or neutral conditions, basic drugs will migrate as uncharged ion pairs if a suitable inoraganic counter ion such as Br − or Cl − is present in sufficient amounts. The latter can be achieved by dissolving halide salts in the developing solvent, or by impregnating the sorbent with halide salts prior to the development. The ion-pair chromatographic systems tested are compared with systems in which the drugs migrate in their basic form and the results suggest that the use of ion-pair system has great potential as a great general screening technique for basic-drugs when carried out in combination with a general basic development system. system.

ABSOLUTE BIOAVAILABILITY OF MICROCRYSTALLINE THEOPHYLLINE

SummaryA study was carried out to investigate the variation in the systemic availability of theophylline after ingestion of a new microcrystalline tablet (‘Theolair”). Serum concentrations obtained after oral administration of the drug were compared with those after intravenous infusion of aminophylline in the same patient. The absolute bioavailability was calculated and oral absorption appeared to be very fast, resulting in maximum serum concentrations after 100±30 min (mean ± S.D.J. Inter-patient variation of maximum serum concentrations was low: 9.8±2.5 μg/ml (mean ± S.D.). The fast absorption resulted in a complete absolute bioavailability with a very low variation: 102.7±10.2 (mean ± S.D.).

ISOLATION AND DETERMINATION OF QUATERNARY AMMONIUM-COMPOUNDS BY MEANS OF AMBERLITE XAD-COLUMNS AND THIN-LAYER CHROMATOGRAPHY

The potentials of XAD-columns for the isolation of quaternary ammonium compounds from aqueous media have been investigated. When adequate amounts of counter ions (perchlorate, chloride, phosphate, nitrate) were added to the aqueous sample, to the column pretreatment fluid and to the aqueous washing fluid, most quaternary compounds investigated were retained on the column and could be recovered by elution with methanol. This approach proved also suitable for urine. Quantitation of quaternaries isolated in this way from urine samples could be performed on silicagel thin layer plates through visualization with iodine, followed by densitometric evaluation. For decamethonium detection limits were 0.1 μg/ml. Recoveries at the 1 μg/ml level were between 80–90% with variation coefficients of less than 10%.