Claire Souppart

Determination of cefsulodin, cefotiam, cephalexin, cefotaxime, desacetyl-cefotaxime, cefuroxime and cefroxadin in plasma and urine by high-performance liquid chromatography

Closely related methods for the determination of several cephalosporins in plasma and urine are described. Deproteinized plasma or diluted urine is directly injected on a RP-8 or RP-18 bonded-material column. Chromatography is performed either in the reversed-phase or the ion-pair mode. The limits of sensitivity range from 0.4 to 2 mumol of cephalosporins per liter of plasma, and from 20 to 100 mumol per liter of urine. The sensitivity may be improved two to five times by using precolumn loading, direct sample clean-up and automatic injection. The stability of the cephalosporins in plasma, urine and water and the reproducibility and accuracy of the methods are reported.

Interaction trial between artemether-lumefantrine (Riamet) and quinine in healthy subjects.

Forty‐two healthy Caucasian subjects were randomized in a double‐blind, parallel three‐group study (14 subjects per group) to investigate potential electrocardiographic and pharmacokinetic interactions between the antimalarials artemether‐lumefantrine (six‐dose regimen of Riamet® over3 days) and quinine (2‐h intravenous infusion of 10 mg/kg body weight, not exceeding 600 mg in total, 2 h after the last dose of Riamet®). The study medications were all safe and well tolerated after all treatments. Neither the pharmacokinetics of lumefantrine nor the pharmacokinetics of quinine was influenced by the presence of the other drug. Plasma levels of artemether and dihydroartemisinin appeared to be lower following the combined treatment Riamet® + quinine, but this was not considered to be clinically relevant. Riamet® alone had no effect on QTc interval. Infusion of quinine alone caused a transient prolongation of QTc interval, which was consistent with the known cardiotoxicity of quinine, with this effect being slightly but significantly greater when quinine was infused after Riamet®. It would thus appear that the inherent risk of QTc prolongation of IV quinine was enhanced by prior administration of Riamet®. However, these occasional QTc prolongations, which were small in magnitude and not correlated with plasma concentrations of any of the compounds, were not considered to be of clinical importance. In conclusion, overlapping therapy with artemether‐lumefantrine and IV quinine in the treatment of patients with complicated or multidrug‐resistant Plasmodium falciparum malaria may result in a modest increased risk of QTc prolongation, but this is far outweighed by the potential therapeutic benefit.

Development of a high throughput 96-well plate sample preparation method for the determination of trileptal (oxcarbazepine) and its metabolites in human plasma

A high throughput preparation method for the determination of trileptal (oxcarbazepine, OXC) and its mono (MHD) and dihydroxy (DHD) metabolites in human plasma, using 96-well plate technology, has been developed and validated according to international regulatory requirements. Preparation of plasma samples (50 microl) containing the compounds to be analysed involved solid-phase extraction (SPE) on Empore C18 96-well SPE plates. Eluates from the plate were injected onto a reversed-phase column (Hypersil C18,3 microm) with UV detection at 210 nm. Detector response was linear over the ranges 0.2-10, 0.1-200 and 0.1-20 micromol/l, for OXC, MHD and DHD, respectively, with relative standard deviations from 1 to 10% and mean accuracies within 4% of the nominal values (number of standard curves=3 in duplicate). The limits of quantitation were 0.2, 0.1 and 0.1 micromol/l, respectively. The overall mean accuracies ranged from 96 to 106% and precision was in the range 4 to 11%. Cross validation indicated no significant difference between plasma concentrations obtained using the 96-well method and the previous method using a traditional SPE method with a 50 mg C18 cartridge. About a threefold increase in sample throughput and a twofold decrease of plasma volume required for the assays, were the main advantages obtained from the previous method. The method was applied for the determination of 3000 plasma samples from clinical studies.

Quantitative assay of sulphinpyrazone in plasma and urine by high-performance liquid chromatography

A method for the quantitative determination of sulphinpyrazone in plasma and urine is described. The drug is extracted from the acidified aqueous phase with 1-chlorobutane-ethylene dichloride (4:1) and separated from its metabolites by high-performance liquid chromatography on 5-mum LiChrosorb using dichloromethane-ethanol-water-acetic acid (79.1:19:1.9:0.002) as the mobile phase. The sensitivity limit is 0,2mug/ml using a 1-ml sample. Examples of applications are given.

Automated analysis of a novel anti-epileptic compound, CGP 33 101, and its metabolite, CGP 47 292, in body fluids by high-performance liquid chromatography and liquid-solid extraction

Automated procedures for the determination of CGP 33,101 in plasma and the simultaneous determination of CGP 33,101 and its carboxylic acid metabolite, CGP 47,292, in urine are described. Plasma was diluted with water and urine with a pH 2 buffer prior to extraction. The compounds were automatically extracted on reversed-phase extraction columns and injected onto an HPLC system by the automatic sample preparation with extraction columns (ASPEC) automate. A Superlosil LC-18 (5 microns) column was used for chromatography. The mobile phase was a mixture of an aqueous solution of potassium dihydrogen phosphate, acetonitrile and methanol for the assay in plasma, and of an aqueous solution of tetrabutylammonium hydrogen sulfate, tripotassium phosphate and phosphoric acid and of acetonitrile for the assay in urine. The compounds were detected at 230 nm. The limit of quantitation was 0.11 mumol/l (25 ng/ml) for the assay of CGP 33,101 in plasma, 11 mumol/l (2.5 micrograms/ml) for its assay in urine and 21 mumol/l (5 micrograms/ml) for the assay of CGP 47,292 in urine.

Determination of oxiracetam in plasma and urine by column-switching high-performance liquid chromatography

A column-switching high-performance liquid chromatographic method was developed for the determination of oxiracetam in plasma and urine. A sample of plasma (250 microliters) or urine (10 microliters) is mixed with the internal standard solution, 4.2 ml of acetonitrile-water (1000:4, v/v) and 0.8 ml of dichloromethane, and 1 ml of the clear solution is injected onto a first column filled with Li-Chrosorb NH2. The sample is eluted with acetonitrile-water (95:5, v/v). The portion of the eluate (heart-cutting) from this column containing the compounds of interest is selected and loaded on a Nucleosil NH2 column and eluted with acetonitrile-water (90:10, v/v). During this chromatography the first column (LiChrosorb NH2) is rinsed with acetonitrile-water (50:50, v/v). Ultraviolet detection at 200 nm is used for quantitation. The limit of quantitation of oxiracetam is ca. 1.5 microM (240 ng/ml) in plasma and 76 microM (12 micrograms/ml) in urine. Oxiracetam was stable in plasma and urine samples kept frozen at -20 degrees C for nine months and one year, respectively.

Pharmacokinetics of Licarbazepine in Healthy Volunteers: Single and Multiple Oral Doses and Effect of Food

Two studies characterized single‐ and multiple‐dose pharmacokinetics of licarbazepine immediate‐release tablets and food effects on single‐dose pharmacokinetics. In 1 study, 12 volunteers received 500 mg licarbazepine on day 1, 500 mg bid on days 3 to 6, and 500 mg on day 7. In the second study, 12 subjects received one 500‐mg licarbazepine dose under fasted and fed conditions. After multiple dosing, geometric mean (%CV) Cmaxss, Cminss, and AUCτ were 77.6 μmol/L (18), 45.3 μmol/L (25), and 747 hṁμmol/L (19), respectively, with a tmax of 2 hours. Mean half‐lives were 9.3 and 11.3 hours for single and multiple dosing, respectively. Food had no clinically significant effect on single‐dose pharmacokinetics. Half‐life (∼10 hours) and low intersubject variability in main pharmacokinetic parameters were similar under fasted and fed conditions. Median tmax increased from 1.5 to 2.5 hours with food. Licarbazepine is well tolerated and has predictable pharmacokinetics.

The Routine Use, and Column-Stability Implications, of Several Column-Switching HPLC Methods for Determining Drugs in Plasma and Urine

Several possible configurations can be used for column-switching systems: trace enrichment on a pre-column and automatic back-flush or forward-flush injection of the purified sample on an analytical column; injection of the sample onto one column and automatic selection of a portion of the eluate (heart-cutting) for chromatography on a second column; combination of these two systems: trace enrichment and heart-cutting. These approaches are briefly described for metoprolol, CGP 6140 and oxiracetam.