G. Cuisinaud

Determination of nalidixic acid and its two major metabolites in human plasma and urine by reversed-phase high-performance liquid chromatography

This paper describes a precise and sensitive method for analysis of nalidixic acid and its two major metabolites in plasma and urine following the oral administration of a therapeutic dose in humans. After addition of an internal standard (oxolinic acid), 1-ml samples of plasma or urine are extracted at acidic pH with chloroform. The extracts are purified by re-extraction with sodium hydroxide solution and then chloroform. The final extracts are evaporated to dryness, reconstituted in mobile phase and injected into a high-performance liquid chromatograph equipped with RP-8 column and UV detector operating at 254 nm. The limit of sensitivity of the method is lower than 0.5 micrograms/ml of plasma or urine for each compound. The applicability of the method to pharmacokinetic studies of nalidixic acid in humans is demonstrated.

Influence of hepatic impairment on the pharmacokinetics of nefazodone and two of its metabolites after single and multiple oral doses

Summary— The pharmacokinetics of nefazodone, a new antidepressant, and two of its active metabolites, hydroxynefazodone and m‐chlorophenylpiperazine, were determined after single and repeated oral escalating doses of 50, 100 and 200 mg, in healthy volunteers (n = 13) and patients with mild (n = 13) or severe (n = 6) hepatic impairment. All subjects were classified according to their dextromethorphan oxidation capacity. In healthy volunteers, nefazodone was rapidly absorbed after which the plasma concentrations declined with an apparent elimination half‐life ranging from 2.7 ± 1.7 h to 10.2 ± 4.4 h according to the dosage. Hydroxynefazodone appeared rapidly in plasma and its time‐course (half‐life ranging 1.4 ± 0.9 h to 6.5 ± 1.6 h) paralleled that of nefazodone, while mCPP showed low and variable concentrations. The disproportionately longer half‐life and more markedly increased Cmax and AUC0–48 which was observed with dosage and treatment duration, and moreover AUC0–12 at steady state significantly higher (P < 0.05) than AUC0–∞ after single dose demonstrated the non‐linearity of the pharmacokinetics of nefazodone and hydroxynefazodone. The constant molar AUC0–48 hydroxy‐nefazodone/nefazodone ratio (0.32 ± 0.04) and the close correlation (r2 = 0.95) between kinetic parameters of nefazodone and hydroxynefazodone suggest that nefazodone hydroxylation is not a saturable process. The kinetics of nefazodone and metabolites were significantly affected by severe but not by mild liver insufficiency. As a consequence, on a pharmacokinetic basis nefazodone should be used with caution in severely hepatic impaired patients.

Measurement of urinary catecholamines and their catechol metabolites and precursor by liquid chromatography with column-switching and on-line fluorimetric and electrochemical detection

A new method is described for the determination of catecholamines and their precursor (3,4-dihydroxyphenylalanine), and separately of their catechol metabolites (3,4-dihydroxymandelic acid, 3,4-dihydroxyphenylacetic acid, 3,4-dihydroxyphenylethylene glycol and 3,4-dihydroxyphenylethanol) in urine. After a two-step pretreatment involving ethyl acetate extraction and adsorption onto alumina, the separation is performed by ion-pair reversed-phase high-performance liquid chromatography. A column-switching system enables complete separation of the most polar compounds without increase in the total analysis time. The column eluates are monitored with both fluorimetric and amperometric detectors, the relative responses of which are used as an index of peak purity. Reference values for twelve healthy adults are given.

Routine analysis of catecholamines and metabolites in urine by a liquid chromatographic column switching system.

A reversed-phase liquid chromatographic technique including a column switching system has been adapted for the routine measurement of catecholamines and their metabolites (14 compounds) in urine. From 1 ml of urine all the compounds and the internal standards were obtained according to combined extraction procedures involving organic solvent, anionic and weakly cationic resins. Finally four extracts (catecholamines, methoxamines, acidic and neutral derivatives) had to be chromatographed throughout a wholly automated apparatus. For each run, the column switching system determined the analytical columns to be used to obtain the separation of the compounds from interferences due to other co-extracted endogenous substances, while the analysis times remained between 20 and 40 min. Such a system allowed the rapid clean-up of columns (in direct- and back-flush mode) carried out between two consecutive injections. By coupling on-line fluorimetric and electrochemical detections the specificity of the technique could be checked, since the ratio of the responses of both detectors was an index of the purity of the peaks. Finally the advanced automation of the equipment allowed weekly the evaluation of catecholamines and the whole range of their known metabolites in 36 urine samples.

Pharmacokinetics of penbutolol and its metabolites in renal insufficiency

SummaryThe pharmacokinetics of penbutolol, its 4-hydroxylated metabolite and of their conjugates was studied in hypertensive patients with various degrees of renal impairment.A single oral dose of penbutolol 40 mg, was rapidly absorbed after a lag-time of 0.34 h. Its plasma concentration reached a maximum after 0.84 h and then declined bi-exponentially, with an apparent elimination half-life of 21.8 h. The hydroxylation of penbutolol was negligible and conjugation was of major importance for its elimination. Consequently, the kinetics of unchanged penbutolol were not altered by renal impairment. The 48 h-urinary excretion of penbutolol and its metabolites reached 13–14% of the administered dose, which is consistent with extensive metabolism of the drug.After treatment for 30 days with penbutolol 40 mg/d there was no accumulation of the parent drug but the concentration of its conjugates was increased.It is concluded that the dose of penbutolol need not be changed in patients with mild renal insufficiency, 4-hydroxypenbutolol is unlikely to participate in the anti-hypertensive effect of the drug, due to its low concentrations, and biotransformation of penbutolol may be enhanced during chronic treatment.

Separation of Twenty Biogenic Amines and Derivatives by a High-performance Liquid Chromatographic Column Switching Technique with On-line Fluorimetric and Electrochemical Detections

Abstract A new high-performance liquid chromatographic technique including the use of an automated column switching system has been developed for the study of dopamine, norepinephrine, epinephrine and serotonin and their related metabolites in biological samples. Through two runs, it has been possible to separate twenty derivatives and three internal standards which have to be added to samples prior to the extraction procedures. In each case, the column switching system allowed to obtain a clear separation of all the compounds, which will be of importance to avoid any expected interference from other endogenous substances, while decreasing the analysis time. By coupling on-line fluorimetric and electrochemical detections the specificity of the technique was enhanced, since the ratio of the responses of both detectors was an index of the purity of the peaks. In addition, fluorimetric detection was found of value to free the determination of some compunds from the effects of solvent front while electrochemi...

Determination of piroximone in Plasma and urine by high performance liquid chromatography

Abstract A reversed-phase high-performance liquid chromatographic (HPLC) method with UV detection was developed for quantifying piroximone (PI) in plasma and urine. A solid phase extraction of PI simultaneously with an internal standard with an average recovery higher than 86% was needed to avoid endogenous interferences especially in urines from patients with reduced renal functions. The sensitivity limit was 2 ng/ml in plasma and 100 ng/ml in urine. The method was reproducible with intra- and inter-assay coefficients of variations below 7 %. This method was applied to the determination of plasma and urine levels during a pharmacokinetic study in healthy subjects and renally impaired patients. It was found suitable to follow the concentrations until 24 h after a single intravenous infusion of 0.5 mg/kg body weight of piroximone.

High-performance liquid chromatographic determination of cicletanide, a new diuretic, in plasma, red blood cells, urine and saliva

A sensitive, selective and easy to use high-performance liquid chromatographic method for the determination of cicletanide, a new diuretic, in plasma, red blood cells, urine and saliva is described. After extraction of cicletanide together with an internal standard with diethyl ether, or diethyl ether-n-hexane (20:80) for urine, the sample extracts are chromatographed with water-methanol-acetic acid (50:50:0.3) as eluent on to a Nucleosil C18 column. Both compounds are detected by their ultraviolet absorption at 280 nm. The calibration graph was linear between 0.2 and 20 micrograms/ml for plasma and between 0.2 and 5 micrograms/ml for the other biological fluids. The sensitivity limit was 20 ng/ml for plasma, red blood cells and saliva and 30 ng/ml for urine. The coefficients of variation of the between-day assays did not exceed 4.6% in plasma, 8.3% in red blood cells, 7.8% in urine and 4.2% in saliva for the lowest concentrations studied. The application of the method to a pharmacokinetic study of cicletanide after a single oral therapeutic dose in humans is reported.

Determination of Chlormezanone in Plasma and Urine by High Performance Liquid Chromatography

Abstract A reversed-phase high-performance liquid chromatographic (HPLC) method with UV detection was developed for quantifying chlormezanone in plasma and urine. an extraction step was needed to avoid endogenous interferences especially in urines and led to an average recovery of 90%. the sensitivity limit was 20 ng/ml in both plasma and urine. the method was reproducible with intra- and inter-assay coefficients of variations below 5%. This method was applied to the determination of plasma and urine levels during a pharmacokinetic study in the elderly. It was found suitable to follow the concentrations as long as 120 h after a single oral administration of 400 mg chlormezanone.

Pharmacokinetics of chlormezanone in elderly patients

SummaryThe pharmacokinetics of Chlormezanone (CM) has been determined after a single oral dose of 400 mg CM in 5 young volunteers (28 y) and in 8 elderly patients (79 y). In the young subjects, CM was rapidly absorbed and distributed, and was slowly eliminated with a half-life of 38 h major metabolites were not detected in plasma or urine. Only 3% of CM was excreted unchanged in urine.In elderly patients absorption was delayed but not reduced; the Cmax and AUC did not differ from those in younger subjects, the elimination rate was reduced compared to the younger subjects (mean 54 h). The increase was in part related to the reduction in renal function and metabolism observed in aging.However, the change in pharmacokinetics was moderate and no adjustment in dosage seems necessary for treatments of limited duration in elderly patients.