Assay of flucytosine and furosemide by high-pressure liquid chromatography

Furosemide assay in pharmaceuticals by Micellar liquid chromatography: study of the stability of the drug

A simplified high-performance liquid chromatographic procedure is described for the determination of furosemide (4-chloro-N-furfuryl-5-sulphamoylanthranillic acid), which makes use of UV detection, a C18, reversed-phase column, and micellar mobile phases of sodium dodecyl sulphate (SDS) and 1-propanol at pH 3 buffered with phosphate system. The most adequate experimental conditions to handle furosemide solutions in the analytical laboratory are studied. The mixture of furosemide and its degradation products which are formed upon light exposition was resolved with a mobile phase of 0.04 M SDS-2% propanol. Separation of furosemide from its common impurities and the hydrolytic product, 4-chloro-5-sulphamoylanthranillic acid, was also possible. A mobile phase of larger elution strength, such as 0.06 M SDS-8%, propanol was preferred to assay furosemide in several dosage forms (tablets, capsules, injectables and drops). The validity of the procedure was checked by analysing 27 pharmaceuticals commercialised in several countries. The label claim percentages and coefficients of variation were in the 95-102% and 0.05-1.3% ranges, respectively. The results showed that the procedure is suitable for routine analysis of the diuretic.

High-performance liquid chromatographic determination of furosemide in plasma and urine and its use in bioavailability studies

A sensitive, selective and efficient reversed-phase high-performance liquid chromatographic (HPLC) method is reported for the determination of furosemide in human plasma and urine. The method has a sensitivity limit of 5 ng/ml in plasma, with acceptable within- and between-day reproducibilities and good linearity (r2>0.99) over a concentration range from 0.05 to 2.00 microg/ml. The one-step extract of furosemide and the internal standard (warfarin) from acidified plasma or urine was eluted through a muBondapak C18 column with a mobile phase composed of 0.01 M potassium dihydrogenphosphate and acetonitrile (62:38, v/v) adjusted to pH 3.0. Within-day coefficients of variation (C.V.s) ranged from 1.08 to 8.63% for plasma and from 2.52 to 3.10% for urine, whereas between-day C.V.s ranged from 4.25 to 10.77% for plasma and from 5.15 to 6.81% for urine at three different concentrations. The minimum quantifiable concentration of furosemide was determined to be 5 ng/ml. The HPLC method described has the capability of rapid and reproducible measurement of low levels of furosemide in small amounts of plasma and urine. This method was utilized in bioavailability/pharmacokinetic studies for the routine monitoring of furosemide levels in adults, children and neonate patients.

Evaluation of liquid chromatographic behavior of restricted-access media precolumns in the course of direct injection of large volumes of plasma samples in column-switching systems

The chromatographic behavior of an alkyl-diol silica (ADS, 25 x 4 mm I.D.) and a semipermeable surface (SPS, 10 x 10 mm I.D.) supports two types of restricted-access media (RAM), which served as precolumns in column-switching systems for direct injection of large volumes of plasma samples (500 microl), was studied with regard to peak performance, retention and column back pressure. The adsorption of matrix proteins both on sealings (porous frits and sieves) and packings was also examined. Columns of ADS and SPS were unchanged after the injection of 10-20 ml human plasma under normal working conditions. Even when changes occurred on the precolumns (>50 ml of plasma in total), it was still possible to regenerate the column performance by replacing the column sieves, or by washing and removing columns from the system for a period, since the changes were more related to the blockage of sealings and/or the adsorption of proteins on the hydrophilic surfaces. Proteins could eventually be unspecifically adsorbed on the hydrophobic ligand of the support. It was found on one ADS column that the retention decreased by 20% and the pressure increased 30 bar after an intensive loading of 75 ml plasma (injection volume, 500 microl) without reconditioning procedure. Studies showed that the column sealings played the most important role for the lifetime of RAM columns. For ADS columns, using sieves without polytetrafluoroethylene (PTFE) nets were the best. No significant difference in column life span between SPS and ADS was found.

Micellar electrokinetic chromatography as a fast screening method for the determination of the doping agents furosemide and piretanide in urine

The possibility of using micellar electrokinetic chromatography for the screening of the loop diuretics piretanide and furosemide in urine was studied. A fast and simple method with good repeatability is described. The method was applied to urine samples collected from a healthy volunteer after oral administration of therapeutic doses of each compound. Positive identification in the urine matrix was possible through recording diode array spectra.

Amphotericin B enzyme-linked immunoassay for clinical use: comparison with bioassay and HPLC

OBJECTIVE

To evaluate a new enzyme-linked immunosorbent assay (ELISA) for amphotericin B in serum samples. Results are compared with those obtained by HPLC and bioassay.

DESIGN

Comparison of results obtained by ELISA, HPLC, and bioassay.

METHODS

We developed a new ELISA using a polyclonal rabbit antibody to measure serum amphotericin B concentrations. Blinded samples of amphotericin B in concentrations of 0.15-78 micrograms/mL were prepared in human serum and assayed simultaneously by the ELISA, HPLC, and bioassay. The results of each assay were derived from standard curves and evaluated by using the Table Curve 2D computer program. These data were compared by using correlation analysis with evaluation of Pearson's correlation coefficient by Student's t-test.

RESULTS

ELISA and bioassay compared favorably at amphotericin B concentrations of 0.3-20 micrograms/mL with a correlation coefficient of r = 0.993, while ELISA and HPLC compared with a correlation coefficient of r = 0.944. The average coefficient of variation over the range 0.3-20.0 micrograms/mL was 28% +/- 7% for HPLC, 26% +/- 9% for ELISA, and 13% +/- 4% for bioassay. Comparison of all three assays revealed the highest correlation with the ELISA assay (r = 0.998) for the range of concentrations (0.3-20 micrograms/mL) routinely achieved. Samples containing concentrations in excess of 20 micrograms/mL could be diluted. Desiccation for concentrations less than 0.3 microgram/mL was not tested.

CONCLUSION

The determination of serum amphotericin B concentrations by ELISA gave results similar to those obtained by a bioassay and HPLC technique. Although variability appears greater with ELISA, the ease of performing yjis assay expedites the evaluation of amphotericin B concentrations from lipid formulations without interference from coadministered antibacterials of azole antifungals.

Determination of piretanide and furosemide in pharmaceuticals and human urine by high-performance liquid chromatography with amperometric detection

A high-performance liquid chromatographic method with electrochemical detection (ED) has been developed for the determination of two diuretics: 4-phenoxy-3-(1-pyrrolidinyl)-5-sulfamoylbenzoic acid (piretanide) and 4-chloro-2-furfurylamino-5-sulfamoylbenzoic acid (furosemide). The chromatographic separation was performed on a mu Bondapak C18 column with a mobile phase of acetonitrile-water (40:60) containing 5 mM KH2PO4/K2HPO4 and with a flow-rate of 1 ml/min (69 bar). The temperature was optimized at 30 +/- 0.2 degrees C. The amperometric detector equipped with a glassy carbon electrode was operated at +1200 mV versus Ag/AgCl in the direct current mode. The method was applied to the determination of these compounds in two concentration ranges (ppm and ppb), obtaining a reproducibility in terms of relative standard deviations lower than 1% for within-day and 4% for day-to-day and determination limits of 15 ppb for both compounds. Recoveries greater than 90% were obtained for spiked urine samples, using a liquid-liquid extraction method in the sample clean-up procedure. The LC-ED method was applied to commercially available pharmaceuticals (Seguril, furosemide 40 mg, and Perbilén, piretanide 6 mg) and urine samples obtained from healthy volunteers and hypertensive patients.

Pharmacokinetics of furosemide in endolymph

To investigate the pharmacokinetics of organic anions in the endolymph of the guinea pig, 100 mg/kg furosemide, an organic anion, was intravenously given to measure the concentration in the cochlear endolymph by high-performance liquid chromatography with fluorescence detection. In the endolymph, the concentration of the furosemide increased slowly for 1 hr to 1.6 micrograms/ml and gradually declined thereafter. Pretreatment with 200 mg/kg probenecid, an anion transport inhibitor, had no effect on the furosemide elimination in the endolymph except on the concentration at 2 hr. This was contrary to the drastic change observed in the perilymph of the scala tympani by the same pretreatment. Analogous to the effect in the endolymph, probenecid showed no change in the concentration of the serum, while a pronounced gradient of furosemide concentration existed between them. The present results suggest that the furosemide passively transfers from blood to the endolymph at a relatively low penetrability.

Pharmacokinetic, biliary excretion, and metabolic studies of 14C-furosemide in the rat

1. Partition of furosemide into organic solvents at pH 3.8 was greatest for ethyl acetate (33:1) greater than 2-ethyl-1-hexanol (10:1) greater than ethyl ether (6:1). 2. Furosemide was highly bound to human, bovine, rabbit, and rat plasma or albumin (97.4-98.4%). 3. Furosemide was highly bound to rat tissues. One hour after i.p. injection of the drug, tissue to plasma concentration ratios were: adrenals (10:1), lung (4:1), kidney (4:1), spleen (3:1). 4. In rats with ligated renal pedicles, furosemide was excreted in bile, at least in part, by active transport. Hepatic clearance of a 1 mg/kg i.v. dose contributed 20% to total body clearance. Large doses (50 mg/kg and more) of furosemide exerted a choleretic effect. 5. Chromatography of bile showed that i.v. administration of 50 mg/kg and higher doses of furosemide to rats resulted in saturation of hepatic drug metabolism. 6. The bile of rats contained the parent drug, 4-chloro-5-sulphamoyl-anthranilic acid, and at least two unknown metabolites with the furan ring intact.

Simultaneous analysis of furosemide and bumetanide in horse plasma using high performance liquid chromatography

A high performance liquid chromatographic method is described for the simultaneous determination of furosemide and bumetanide in horse plasma. The C8 (3 microns) reversed phase column (4.8 x 150 mm) provided clear separation of furosemide and bumetanide with other components present in the horse plasma. The detection limit for both the drugs was 10 ng/mL. Both drugs were stable in plasma (at natural or acidic pH) for up to 24 h. The method is sufficiently sensitive to detect furosemide levels in plasma obtained from horses receiving a therapeutic dose of furosemide.

Determination of antibiotics and antimicrobial agents in human serum by direct injection onto silica liquid chromatographic columns

Antibiotics and antimicrobial agents are therapeutically monitored by the direct injection of untreated human serum onto silica columns. This simple approach does not lead to rapid column deterioration since the eluents utilized are almost totally aqueous and, consequently, prevent precipitation of the serum protein on the column. Column capacity of the drugs studied varies due to the mutual interaction of the eluent ionic buffer and organic modifiers. The influence of the number of serum injections on column-back pressure, column capacity and quantitative analyses is discussed.

Determination of furosemide in rat plasma using HPLC and liquid scintillation

A rapid and convenient HPLC method for the determination of furosemide in plasma is described. The method uses a buffered mobile phase containing 22% (v/v) acetonitrile. The precision, detection limit and the correlation between the HPLC method and a liquid scintillation determination of furosemide are satisfactory. A pharmacokinetic study of furosemide in the rat is described.

Improved procedure for determination of flucytosine in human blood plasma by high-pressure liquid chromatography

Several high-pressure liquid chromatography procedures for the determination of flucytosine in serum or plasma have appeared. Some of these suffer from significant disadvantages, and none was applicable in our routine clinical therapeutic-drug-monitoring laboratory. A new high-pressure liquid chromatography assay for flucytosine was therefore developed. A 100-microliter sample of plasma was treated with an aqueous 5-iodocytosine internal-standard solution, and the mixture was deproteinized with trichloroacetic acid. A portion of the protein-free supernatant was diluted with 0.1 M ammonium phosphate, and an aliquot of the resulting solution was injected into the high-pressure liquid chromatography system. Chromatography was performed on a strong-cation-exchange column with a mobile phase containing aqueous ammonium phosphate, phosphoric acid, methanol, and acetonitrile. Detection was at 254 nm. The assay was shown to be linear in the 10 to 200-micrograms/ml drug-concentration range. Forty other drugs were tested for potential interference with the assay, and none was found. For routine use, a single-point working standard containing 75 micrograms of flucytosine per ml was used, giving intraassay coefficients of variation at 50 and 150 micrograms/ml of 1.8 and 2.3% respectively, whereas the day-to-day coefficient of variation at 50 micrograms/ml was 10.0%. Advantages of the procedure include the small sample size, the use of a convenient and reliable internal standard, speed, and simplicity. The assay is highly suitable for routine clinical drug-analysis laboratories.

Specimen handling and high-performance liquid chromatographic determination of furosemide

A simple high-performance liquid chromatographic method to measure furosemide in plasma and urine is described. Furosemide fluoresces best, but is unstable, at acidic pH and is subject to photochemical degradation. These factors were analysed and the results prompted changes in previously described methods. All specimens were very carefully protected from light; extraction and acidification were done with acetic acid instead of hydrochloric acid. With these precautions no 4-chloro-5-sulphamoylanthranilic acid was found in biological specimens. The main metabolite was furosemide glucuronide (20% of furosemide excretion). Sensitivity was 0.1 and 0.5 microgram/ml for plasma and urine, respectively. The applicability of our method for furosemide studies is demonstrated.

Improved method for the analysis of furosemide in plasma by high-performance liquid chromatography

Modifications of existing rapid high-performance liquid chromatographic procedures for the determination of furosemide in plasma were made in order to achieve greater sensitivity. To a small volume of plasma was added in internal standard structurally related to furosemide. Then, following previously described procedures, acetonitrile was added to precipitate the proteins and the clear supernatant was separated. However prior to injection of the supernatant the pH and composition of the sample were adjusted. This modification of the sample enabled an injection volume of up to 300 microliters of the supernatant to be injected onto the chromatographic column. The effluent was monitored spectrofluorimetrically. A standard linear calibration curve with a mean precision of +/- 4.4% was obtained for plasma samples containing 20--900 ng/ml of furosemide. Two structurally related compounds were used as internal standards in the furosemide assay.

Liquid chromatographic assay of ketoconazole

A reverse-phase, high-pressure liquid chromatographic method for the rapid and quantitative determination of ketoconazole has been developed. Drug levels from 0.5 to 10 microgram/ml can be determined in either yeast nitrogen base medium or human serum by using an octadecylsilane column. A retention time of 4.9 +/- 0.1 min resulted when the drug was eluted from a column with 75% methanol-25% 0.02 M (pH 7.5) phosphate buffer at a flow rate of 2 ml/min. Optimum sensitivity was obtained at a wavelength of 231 nm.

Pharmacokinetics/pharmacodynamics of furosemide in man: a review

The pharmacokinetics of furosemide and the attempt to correlate biological fluid measurements with diuretic response have been the subject of a large number of studies since the original reports of Hajdú, Rupp, and coworkers in the mid-1960s. This article attempts to critically review these studies under seven different sections: furosemide pharmacokinetics in normal volunteers, furosemide pharmacokinetics in patients with decreased renal function, furosemide pharmacokinetics in patients with congestive heart failure, furosemide metabolism and assay methods, furosemide bioavailability, dose-response relationships, and the role of inhibitors and mediators on furosemide effects. The literature is reviewed through August 1978.

Determination of flucytosine in tablets by differential pulse polarography

A differential pulse polarographic assay was developed for determining flucytosine in tablets. The drug is extracted from the sample with water and hydrochloric acid and, after the pH is adjusted, an aliquot is added to the cell and the solution is polarographed at the dropping mercury electrode versus the saturated calomel electrode with 0.066 M Sørensen phosphate buffer (pH 5.6) as the supporting electrolyte. The polarographic peak height enables precise quantitative determination. The Ep value for flucytosine is--1.54 v versus the saturated calomel electrode. The mean recovery of the drug is 101.5% +/- 1.9 (SD). The method is simple, rapid, and precise.

A simplified assay of furosemide in plasma and urine by high-pressure liquid chromatography

A simplified high-pressure liquid chromatograhic method for determination of furosemide in plasma and urine has been developed using a fluorometric detector directly coupled to the column effluent. The method includes an ether extraction from acidified biologic samples. The mobile phase used for chromatography on a reversed-phase column (C15 hydrocarbon permanently bonded to silica particles) is sufficiently acidic to induce fluorescence of furosemide. The methylester of furosemide is employed as an internal standard. The sensitivity is 0.1 and 0.25 microgram per ml plasma and urine, respectively. The applicability to pharmacokinetic studies of furosemide is shown.

Assay of gentamicin in serum by high-pressure liquid chromatography

A procedure is described that uses high-pressure liquid chromatography for assay of gentamicin in serum. The technique involves extraction of gentamicin from serum by using a CM-Sephadex column and analysis by reverse-phase, ion-pair chromatography. Continuous-flow, post-column derivatization with o-phthaladehyde is used to form fluorescent products for detection. The possible scope of this method for analysis of other aminoglycoside antibiotics is illustrated by application to sisomicin and netilmicin.

Quantitation of antibiotics using high-pressure liquid chromatography: tetracycline

A method for quantitative determination of tetracycline in serum, using high-pressure liquid chromatography, is reported. After extraction of the drug from serum, using methanol-trichloroacetic acid solution, tetracycline was separated by reverse-phase chromatography. Quantitation of tetracycline was based on a linear relationship between peak heights in the chromatograms and known concentrations of the drug in the original serum samples. Serum tetracycline concentrations as low as 0.3 mug/ml could be accurately measured. Serum samples obtained after a single intravenous injection of tetracycline to three human volunteers and six dogs were assayed by microbiological and chemical assays. Correlation coefficients of 0.95 and 0.97, respectively, were found. This chemical method is rapid (less than 30 min), accurate, sensitive, and reproducible, and it seems feasible for routine clinical use.