Use of the ASTED system to determine L-NG-monomethylarginine (546C88) in human plasma by pre-column o-phthalaldehyde derivatisation and high-performance liquid chromatography.

The use of the system automated sequential trace enrichment of dialysates (ASTED), to prepare plasma samples for the estimation of L-NG-monomethylarginine (546C88) by pre-column o-phthalaldehyde-2-mercaptoethanol derivatisation and HPLC is described. Calibration is achieved using purified albumin as a substitute matrix for plasma. Using this technique the procedure was observed to be specific for 546C88 and linear over the range 0.10 to 50.0 mumol/l. The within-run imprecision (C.V.) at four different spiked plasma 546C88 concentrations of 0.10, 1.0, 8.0 and 40.0 mumol/l was 6.48, 2.55, 2.79 and 3.37%, respectively, and the between-run imprecision (C.V.) estimated to be 8.50, 1.80, 2.10 and 3.30%, respectively, for the same spiked 546C88 concentrations. The overall accuracy (% bias) of the procedure using an albumin matrix for calibration was estimated to be -2.50, -5.25, -3.56, -3.53%, respectively, and the recovery of 546C88 from six different spiked plasma samples estimated to be 99.1 +/- 1.4%.

Comparison of the pharmacokinetics of lamotrigine in patients with chronic renal failure and healthy volunteers.

AIMS: The aim of this study was to compare the pharmacokinetics of the anti-epileptic agent, lamotrigine, in patients with chronic renal failure and healthy volunteers. METHODS: Non-compartmental pharmacokinetics of a single oral dose (200 mg) of the anti-epileptic agent, lamotrigine, and its main metabolite, lamotrigine N2-glucuronide, were determined for 10 patients with chronic renal failure of mean estimated creatinine clearance 18 ml min-1 and a control group of 11 healthy volunteers, matched for age and gender. RESULTS: For lamotrigine, there were no significant differences in Cmax, tmax, AUC, t1/2,z, CL/F and amount excreted in urine although t1/2,z tended to be longer for the renal failure group with a mean (+/-s.d.) of 35.9 +/- 10.7 h vs 27.8 +/- 4.3 h for the control group. For the renal failure group. VZ/F was 18% higher (95% CI 1% to 39%) compared with controls and CLR was reduced to 61% (95% CI 46% to 80%) of the control group value. For lamotrigine glucuronide, Cmax was increased 4-fold (95% CI 3.1 to 5.3) and AUC 7.8-fold (95% CI 6.0 to 10.1) in the renal failure group compared with controls. CLR was approximately 9-fold lower and apparent t1/2 was increased by 53% (95% CI 27% to 84%). Concentrations of an N2-methylated cardio-active metabolite, previously observed in dogs, were below the limit of detection (2 ng ml-1) of the ASTED/h.p.l.c. assay in the renal failure group as well as controls. CONCLUSIONS: These results indicate that impaired renal function will have little effect on the plasma concentrations of lamotrigine achieved for a given dosing regimen.

Simultaneous determination of lamotrigine and its glucuronide and methylated metabolites in human plasma by automated sequential trace enrichment of dialysates and gradient high-performance liquid chromatography.

The use of the system, automated sequential trace enrichment of dialysates (ASTED), to prepare plasma samples for the estimation of lamotrigine, its glucuronide and methylated metabolites in plasma prior to gradient high-performance liquid chromatography (HPLC) is described. Using this technique the procedure was observed to be specific for all three compounds and linear over the range 0.04 to 10 microg/ml for lamotrigine and the glucuronide metabolite and 2 to 500 ng/ml for the methylated metabolite. The within-run precision (C.V.) at four different supplemented plasma lamotrigine concentrations of 0.04, 0.10, 2.5 and 10.0 microg/ml was 6.21, 5.17, 1.29 and 0.73%, respectively, and the between-run precision (C.V.) estimated to be 13.49, 6.08, 1.95 and 1.78%, respectively. The overall accuracy (% bias) of the procedure was estimated to be 12.50, 0.00, 2.80 and 1.80%, respectively. The glucuronide and methylated metabolites in plasma showed similar assay performance.

Automated sequential trace enrichment of dialysates combined with high-performance liquid chromatography and automated heart-cutting for the determination of the nucleoside 1-(beta-D-arabinofuranosyl)-5-(1-propynyl)uracil and its metabolite 5-propynyluracil in urine.

The use of a new configuration to control the automated sequential trace enrichment of dialysate (ASTED) system has been used to estimate 1-(beta-D-arabinofuranosyl)-5-(1-propynyl)uracil and its metabolite 5-propynyluracil in urine. The system employs "heart-cutting" as a means to improve the efficiency of sample preparation and reduce analysis time. Using this technique the mean within- and between-run imprecision (coefficient of variation) at three different urine analyte concentrations was found to be 1.6 and 3.6% and 1.7 and 3.3% for 5-propynyluracil and 1-(beta-D-arabinofuranosyl)-5-(1-propynyl)uracil, respectively.

Determination of 1-(beta-D-arabinofuranosyl)-5-(1-propynyl)-uracil and a metabolite, 5-propynyluracil, in plasma using ASTED (automated sequential trace enrichment of dialysates) combined, on-line, with high-performance liquid chromatography.

A high-performance liquid chromatographic assay was developed for the determination of the potential antiviral drug 1-(beta-D-arabinofuranosyl)-5-(1-propynyl)uracil (I) and a metabolite, 5-propynyluracil (II), in plasma. Plasma samples were mixed with monochloroacetic acid to reduce the effect of protein binding. The mixture was dialysed prior to concentration of analytes on an ODS cartridge followed by isocratic separation on an ODS analytical column using acetonitrile in aqueous ammonium acetate. Detection was by ultraviolet absorption. The quantifiable limit for both I and II is 0.2 mumol/l with a mean inter- and intra-assay precision of 1.3-2.5% (coefficient of variation).