H. Spahn

Enantiospecific High-Performance Liquid Chromatographic (HPLC) Determination of Baclofen and Its Fluoro Analogue in Biological Material

A method is described for the quantification of baclofen enantiomers in biological material (urine, plasma, and cerebrospinal fluid). The samples were extracted by liquid–solid extraction using Sep-Pak CIS cartridges. The subsequent derivatization procedure contained two separate steps. (1) The butyl esters of the enantiomers were formed using butanolic hydrochloric acid (followed by ion-pair extraction of the intermediate products). (2) A chiral derivatization was then performed using S-( + )-naproxen chloride as reagent. S-( + )-Benoxaprofen chloride can also be used. The diastereomeric amides were separated by high-performance liquid chromatography (HPLC) on a silica gel column (mobile phase, n-hexane/dichloromethane/ethanol; detection, fluorescence measurement at 335/365 nm). The described procedure was also used for the quantification of the fluoro analogue of baclofen. Urinary excretion of baclofen enantiomers was investigated in two healthy volunteers after p.o. administration.

Pharmacokinetics of amiloride in renal and hepatic disease

SummaryThe pharmacokinetics of the antikaliuretic amiloride has been studied in healthy controls and in patients with chronic renal failure or hepatitis. It was 40% bound to protein.In healthy volunteers 49% of an oral dose was recovered unchanged in the urine. The renal clearance of amiloride was about 3 times the creatinine clearance, which means that it was predominantly excreted via tubular secretion.Renal impairment reduced the clearance of amiloride, causing a prolongation of the t1/2 and drug accumulation in plasma. In hepatitis the t1/2 of amiloride was prolonged and the AUC increased. Urinary recovery (Ae) of amiloride was greater in hepatitis patients than in controls.

Chiral Amines Derived from 2-Arylpropionic Acids: Novel Reagents for the Liquid Chromatographic (LC) Fluorescence Assay of Optically Active Carboxylic Acid Xenobiotics

For the enantiospecific analysis of optically active carboxylic acids, the availability of readily detectable coupling components is desirable, but highly fluorescent chiral amines are rare. From activated enantiomers of fluorescent 2-arylpropionic acids fluorescent chiral amines were synthesized via Curtius degradation, i.e., under formation of the acyl azide, the isocyanate, and finally, the amine. The formation of isocyanates and of amine hydrochlorides led to an inversion of the direction of rotation of polarized light. Amines derived from R- and S-flunoxaprofen, R- and S-naproxen, and R/S-benoxaprofen were characterized. The amines were found to be applicable for the chiral separation of carboxylic acids (such as 2-arylpropionic acids) as diastereomeric derivatives via high-performance liquid-chromatographic (normal and reversed-phase) and thin-layer chromatographic techniques.

Activated α-alkyl-α-arylacetic acid enantiomers for stereoselective thin-layer chromatographic and high-performance liquid chromatographic determination of chiral amines

Abstract The separation of racemic benoxaprofen into the two benoxaprofen enantiomers by preparative high-performance liquid chromatography and the application of the activated enantiomers as derivatization reagents for the simultaneous stereoselective determination of chiral amines in biological material is described. Activated (+)- and (−)-benoxaprofen are both shown to be very sensitive and stable chiral fluorescence markers, applicable to thin-layer chromatography as well as to high-performance liquid chromatography.

Single- and multiple-dose pharmacokinetics of R-(−)- and S-(+)-prenylamine in man

SummaryThe pharmacokinetics of S-(+)- and R-(−)-prenylamine was studied in eight healthy volunteers given single and repeated oral doses of the racemic drug.Distinct differences in various pharmacokinetic parameters were found between the S- and R-enantiomer. The maximum plasma concentrations and AUCs of the R-enantiomer exceeded those of the S-enantiomer five-fold; the apparent oral clearance of the S-form was five-times and the renal clearance three-times higher than of the R-form.Acid catalyzed hydrolysis of urine samples released more S-prenylamine, indicating stereoselective glucuronidation of unchanged prenylamine. Plasma protein binding also differed between the two enantiomers, generally with a higher unbound fraction of the S-form, whereas analysis of the bound fractions showed that prenylamine was bound to different plasma proteins with inverse stereoselectivity.

Pharmacokinetics of torasemide and its metabolites in healthy controls and in chronic renal failure

SummaryThe pharmacokinetics of 20 mg torasemide i.v. has been studied in 7 healthy controls and 9 patients with varying degrees of renal impairment.Torasemide had a t1/2 of about 4 h which was independent of kidney function, as the nonrenal clearance of torasemide was 3-times greater than its renal clearance. The active metabolite M1 and the main metabolite M5 were accumulated in chronic renal failure.In contrast to liver function, therefore, kidney failure does not have an important effect on the pharmacokinetics of torasemide.

Simultaneous determination of (R)- and (S)-celiprolol in human plasma and urine: high-performance liquid chromatographic assay on a chiral stationary phase with fluorimetric detection.

The quantitative enantiospecific determination of the beta 1-selective adrenergic antagonist (R,S)-celiprolol in human plasma and urine is described. It involves a two-step liquid-liquid extraction of celiprolol from biological material and separation of the underivatized enantiomers by high-performance liquid chromatography on a chiral stationary phase (cellulose tris-3,5-dimethylphenyl carbamate, coated on silica gel) with fluorimetric detection. R-(+)-Propranolol was used as an internal standard. The detection limits of 1.5 ng/ml enantiomer in plasma and 2.5 ng/ml enantiomer in urine at signal-to-noise ratios higher than 3 permit the performance of pharmacokinetic studies after therapeutic doses.

The loop diuretic torasemide in chronic renal failure : pharmacokinetics and pharmacodynamics

SummaryThe pharmacodynamic effect of a diuretic agent is essentially dependent on its renal elimination characteristics. The influence of renal function on the pharmacodynamic and pharmacokinetic characteristics of a diuretic should therefore be considered. The results of a study with torasemide given intravenously in healthy subjects and in patients with stable chronic renal failure of various degrees are reported and discussed.After a single dose of torasemide 20mg, a marked diuresis was observed and electrolyte excretion was increased, whereas the glomerular filtration rate was unchanged. Throughout the duration of action (τ) of torasemide, drug-induced excretion of Cl−, Na+, K+, Ca++ and Mg++ was linearly related to the creatinine clearance (CLcr), and excretion of K+ and Ca++ were closely related to that of Na+ over the entire range of CLcr. Similarly, excretion of Mg++ was related to that of K+. As occurs with furosemide (frusemide), torasemide induced a kaliuresis which amounted to 12% of natriuresis. This kaliuretic effect of loop diuretics is less than that of thiazides. Beyond τ, e.g. over a 24-hour period, kaliuresis was no longer correlated with natriuresis. The extent to which a rebound effect occurred was diminished with increasing renal impairment.τ averaged 6 hours and was independent of CLcr. The mean half-life (t½) of torasemide was approximately 5 hours and was independent of renal function, since renal clearance accounted for only around 25% of total body clearance. In contrast to the parent drug, however, the active minor metabolite M1 and the inactive main metabolite, M5, were found to accumulate in patients with chronic renal failure.

Rapid determination of the enantiomers of metoprolol, oxprenolol and propranolol in urine

A method is described that makes possible the rapid determination of the enantiomers of beta-blocking agents. After extraction from urine samples (at pH 9.9) using toluene, the enantiomers are derivatised with S-(+)-benoxaprofen chloride. The chromatographic separation can be performed on thin-layer plates with toluene-acetone as mobile phase. The derivatives can be detected by measuring the fluorescence (lambda ex = 313 nm,lambda em = 365 nm).

Simultaneous determination of R- and S-prenylamine in plasma and urine by reversed-phase high-performance liquid chromatography☆

A high-performance liquid chromatographic method for the determination of R- and S-prenylamine in human plasma and urine is described. It involves a two-step liquid-liquid extraction of prenylamine from biological material and preparation of diastereomeric urea derivatives with R-(-)-naphthylethyl isocyanate, a chiral fluorescence marker. Separation and quantitation of the diastereomeric prenylamine derivatives are carried out by a reversed-phase high-performance liquid chromatographic system with fluorimetric detection. The limit of determination is less than 2 ng of enantiomer per ml of urine and less than 1 ng of enantiomer per ml of plasma. A preliminary kinetic study on one healthy volunteer who had received a single oral dose of racemic prenylamine (100-mg film tablet) showed distinctly higher plasma and urine concentrations of the R-enantiomer.