High-performance liquid chromatographic determination of alfuzosin in biological fluids with fluorimetric detection and large-volume injection.

A high-performance liquid chromatographic method has been developed for the determination of alfuzosin, a new antagonist of alpha 1 post-synaptic adrenergic receptors, in blood, plasma or urine. With fluorimetric detection and the large volume injection technique, the limit of detection in plasma is 0.5-1 ng ml-1, which is sensitive enough for pharmacokinetic studies in man. The calibration graph is linear between 1 and 200 ng ml-1 in blood plasma, with coefficients of variation of 6.2 and 1%, respectively. In urine, the linearity range is 0.05-10 micrograms ml-1; at the lowest concentration, the coefficient of variation is about 10%. A constant plasma/blood concentration ratio (1.25 +/- 0.05) allows the measurement of drug in either fluid. In blood or plasma, alfuzosin is stable at 37 degrees C for 24 h and at -20 degrees C for 6 months. As expected for reversed-phase chromatography, the retention times of alfuzosin and a few of its analogues decrease inversely with the concentration of acetonitrile in the mobile phase. However, as this concentration reaches about 75%, the retention times increase sharply. This U-shaped curve may be explained by interactions of the amino groups with silanol groups of the stationary phase.

Plasma and urinary kinetics of furosemide in newborn infants.

Plasma and urinary furosemide kinetics were assayed by high-power liquid chromatography in six newborn infants receiving furosemide (1 mg/kg body weight IV) for the treatment of fluid overload. Mean +/- SD for plasma half-life, apparent volume of distribution, and plasma clearance were, respectively, 9.5 +/- 4.4 hours, 173 +/- 28 ml/kg, and 15.3 +/- 8.4 ml/hr/kg. There was close correspondence between plasma and urinary half-lives and between plasma clearance and renal clearance. In the first 24 hours, mean estimated urinary recovery of unchanged furosemide was 90% of the injected dose (range 61% to 106%). The results suggest that in the newborn infant furosemide is virtually all excreted unchanged in the urine and that the absence of significant nonrenal elimination, together with the immaturity of neonatal renal function, accounts for its prolonged half-life in newborn infants.

Pharmacokinetics of furosemide in neonates.

The pharmacokinetics of furosemide was evaluated in 12 newborns who received the drug transplacentally, and in 21 neonates who received it directly for therapeutic reasons. In the first group, the apparent plasma half-lives ranged from 96 to 6.8 h with a significant inverse relationship (p less than 0.01) between the gestational age and the elimination rate. In two cases a clear effect on diuresis was also observed. In the neonates receiving the drug i.v. for therapeutic reasons, the elimination kinetics appeared to follow a two-compartment open model, with a significant difference in the therminal plasma half-life between premature (26.8 +/- 12.2 h) and full-term newborns (13.4 +/- 8.6 h). In this group no relationship was observed between elimination rate and either gestational or conceptional age. In the case of repeated administration, an increase in plasma clearance and reduction in t1/2 beta was noticed.

Quantitative determination of naproxen in plasma by a simple high-performance liquid chromatographic method.

A high-performance liquid chromatographic method for the determination of naproxen in plasma is described. The technique is based on the single extraction of the drug from acidified plasma with chloroform using 2-naphthalene acetic acid as internal standard. The chromatographic system consisted of a column packed with Spherisorb ODS (5 micrometer); the mobile phase was acetonitrile--phosphoric acid (pH 3) (45:55, v/v). The method can accurately measure plasma naproxen concentrations down to 1 microgram/ml using 100 microliter of sample, with no interference from endogenous compounds. The coefficients of variation of the method at 120 microgram/ml and 1 microgram/ml are 2.8 and 21.6%, respectively, and the calibration curve is linear. The method described is very suitable for routine clinical and pharmacokinetic studies.

Determination of antrafenine and its main acid metabolite, 2-{[7-(trifluoromethyl)-4-quinolinyl]amino}-benzoic acid, in biological fluids using high-performance liquid chromatography with large volume automatic injection and gas-liquid chromatography with derivative formation.

Specific and sensitive analytical methods have been developed for the measurement of antrafenine and its main acid metabolite, 2-([17-(trifluoromethyl)-4-quinolinyl] amino) benzoic acid (FQB), at therapeutic concentrations in plasma and urine. Following the addition of internal standards (the methyl ester of FQB and 2-([8-(trifluoromethyl)-4-quinolinyl] amino) benzoic acid) the parent drug and the metabolite were extracted from biological material with diethyl ether at a weakly acid pH. Drug extracts were evaporated to dryness prior to chromatographic analysis. Antrafenine was measured by high-performance liquid chromatography using a Spherisorb 5-micrometer ODS column with acetonitrile-0.1 M sodium acetate as the mobile phase. Samples were injected automatically using a 500-microliter injection loop. The detector wavelength was 353 nm corresponding to the maximum UV absorption of both drug and internal standard. The coefficient of variation (C.V.) for the determination of antrafenine concentrations between 5 and 250 ng/ml ranged between 24 and 3%, respectively. The acid metabolite of antrafenine was measured by gas-liquid chromatography with electron-capture detection using a 1 m column packed with 3% OV-225 on Gas-Chrom Q (100-120 mesh) at 240 degrees C and on-column methylation with trimethylphenyl ammonium hydroxide. The C. V. of the method for the analysis of metabolite concentrations between 10 and 500 ng/ml ranged between 3 and 9%, respectively.

Determination of nifuroxazide in biological fluids by automated high-performance liquid chromatography with large-volume injection.

A high-performance liquid chromatographic method for the measurement of nifuroxazide in plasma is described. The technique is based on the single extraction of the drug from buffered plasma with chloroform, using nifuratel as internal standard. The chromatographic system consisted of a 15 cm x 4.6 mm I.D. stainless-steel column packed with Spherisorb ODS, 5 micrometer, and the mobile phase was acetonitrile-orthophosphoric acid (pH 2.5) (30:70). The method was able to measure accurately plasma nifuroxazide concentrations down to 2 ng . ml-1 using 2 ml of sample with no interference from endogenous compounds. The coefficients of variation of the method at 200 and 2 ng . ml-1 were 3% and 15%, respectively, and the calibration graph was linear in this range. The use of automatic injection makes the method suitable for the routine analysis of large numbers of samples.