Determination of hydroxyurea in capsules and biological fluids by ion-selective potentiometry and fluorimetry

Two hydroxyurea selective electrodes were investigated with beta-cyclodextrin used as ionophore and either tetrakis (p-chlorophenyl) borate (electrode 1), or tetrakis [3,4-bis (trifluoromethyl) phenyl] borate (electrode 2), as a fixed anionic site in a polymeric matrix of carboxylated polyvinyl chloride. Linear responses of hydroxyurea within a concentration range of 10(-5)-10(-)3 M with slopes of 51.2 and 58.6 mV/decade with pH 3-6 were obtained by using electrodes 1 and 2, respectively. Two spectrofluorimetric methods involving the formation of drug-AI(III) complex (method 3) and drug-Mg(II) complex (method 4) at pH 5 were also investigated. These complexes emit fluorescence at wavelengths of 380 and 355 nm, after excitation at 305 nm, for AI and Mg complexes, respectively. The calibration graphs were rectilinear from 0.5 to 2.5 microg/mL for the AI complex and 1 to 5 microg/mL for the Mg complex. The 4 proposed methods display useful analytical characteristics for determination of hydroxyurea, with average recoveries of 100.2 +/- 0.83 and 99.4 +/- 1.81% in capsules and 99.7 +/- 0.70 and 99.4 +/- 1.25% in biological fluids for the potentiometric and fluorimetric methods, respectively. Results obtained by the proposed procedures were statistically analyzed and compared with those obtained by the U.S. Pharmacopeial method. The 4 proposed procedures were also used to determine the stability of the drug in the presence of its degradate, hydroxylamine.

Determination of hydroxyurea in plasma and peritoneal fluid by high-performance liquid chromatography using electrochemical detection

A sensitive method has been developed for the determination of hydroxyurea in plasma and peritoneal fluid using reversed-phase high-performance liquid chromatography (HPLC) with electrochemical detection. Plasma or peritoneal fluid samples were treated with acetonitrile to precipitate proteins then injected to the HPLC. A C18 analytical column was used to separate hydroxyurea from interfering substances in the biological matrix. The mobile phase, consisting of 0.2 M sodium perchlorate-methanol (95:5, v/v) adjusted to pH 5.0, was delivered isocratically at a flow-rate of 1 ml/min and hydroxyurea was detected using a glassy-carbon electrode operating at an applied potential of +800 mV. Hydroxyurea eluted with a retention time of 3 min. The cycle time for analysis is short and the assay precision is acceptable (C.V. plasma=1.4-3.9%. C.V. peritoneal fluid=2.1-9.7%). The method has been validated and is linear from 25 to 400 ng/ml in plasma and 5 to 30 ng/ml in peritoneal fluid. The method has been shown to be applicable for pharmacokinetic studies.

Determination of 1-benzo[b]thien-2-ylethanone and related impurities by high performance liquid chromatography

1-Benzo[b]thien-2-ylethanone (2-acetylbenzothiophene, 2-ABT) and related impurities were determined using a reverse-phase high performance liquid chromatography system and UV detection at 254 nm. Separation was achieved isocratically on a 4.6 mm x 25 cm, 5 microns Zorbax Rx-C8 column using an eluent which is 0.2% perchloric acid/THF in a ratio of 60:40 (v/v). The chromatographic system resolved 2-ABT and known impurities in less than 45 min with near baseline resolution. Known impurities were quantitated versus 2-ABT with corrections made for differences in detector response at the specified wavelength. Linearity for 2-ABT was demonstrated with a correlation coefficient > 0.9999. Assay precision (RSD values) for impurities at 0.5% ranged from +/- 1.8% to +/- 14%, while precision (RSD values) for the 2-ABT determination ranged from +/- 0.81% to +/- 1.1%. A variety of different chromatographic columns and conditions are discussed for the application.

Analysis of hydroxyurea in capsules and aqueous solution and stability study with capillary gas chromatography and thermionic (N-P) specific detection

A method for the analysis of hydroxyurea (HU) in solutions, powder, or capsules by use of capillary gas chromatography with N-P thermionic specific detection is described. Upon injection of an HU solution in a methanol and acetone mixture, the drug formed pyridine which was well separated from the internal standard (thiotepa) on a 30-m fused-silica, SE-30 capillary column with temperature programming. The peak height ratio versus concentration standard curves were linear with correlation coefficient ranging between 0.9942 and 0.9993. The coefficients of variation at 5, 25, and 50 micrograms/L were 7.2, 5.7, and 5.5%, respectively. Hydroxyurea was extracted from powder or capsule formulations with a mixture of methanol and acetone (50:50, v:v), and the percentage found of the label claim for 10 capsules ranged between 96.7 and 104.9 (mean = 100.1; CV = 2.7%). Further, this assay was used to examine the stability of hydroxyurea in aqueous solutions at 4, 23, and 45 degrees C, and the apparent first-order rate constants observed at these temperatures were 0.06407, 0.08113, and 0.1293 day-1, respectively; the activation energy was 3011 cal.K-1.mol-1.

Quantitative analysis of hydroxyurea and urea by proton nuclear magnetic resonance (NMR) spectroscopy

Quantitative 1H-nuclear magnetic resonance (NMR) procedures are described for measuring hydroxyurea and urea. Dimethylsulfoxide-d6 is used as the solvent for both assays; the internal standards employed are urea and p-dichlorobenzene for hydroxyurea and urea, respectively. The analysis for hydroxyurea is based on the comparison of the area of the -NH2 peak of hydroxyurea with the area of the urea -NH2 peak area. The analysis of urea is based on the comparison of the -NH2 peak of urea with the area of the p-dichlorobenzene singlet. The 1H-NMR assays yield results that are precise and agree well with results of the more cumbersome and less specific USP procedures.

A rapid colorimetric assay for carbamyl phosphate synthetase I

A rapid, reproducible, and sensitive colorimetric assay for carbamyl phosphate synthetase I was presented. A four-fold increase in sensitivity and reduced assay time were afforded by this procedure. The method utilized the chemical conversion of carbamyl phosphate to hydroxyurea by the action of hydroxylamine instead of employing a coupling enzyme. The hydroxyurea was quantitated in 15 min by an improved colorimetric assay for ureido compounds by measuring the absorption of the resulting chromophore at 458 nm. Optimum conditions for both the formation and quantitation of hydroxyurea were established. Activity measurements of carbamyl phosphate synthetase I obtained by this uncoupled method were identical with those obtained by the ornithine transcarbamylase coupled assay.

Solvent-dependent conformational system in hydroxyureas detected by NMR spectroscopy

The proton magnetic resonance spectra of the antileukemia agent hydroxyurea and substituted hydroxyureas in several solvents were recorded and correlated with structural features. Solvent-dependent differences in conformational preferences due to effects on internal hydrogen bonding, a temperature-dependent conformational feature, anthe exchangeability of protons with deuterium oxide and acetone-d6 were observed. The conformational features consistent with the spectral data are discussed.