Determination by high-performance liquid chromatography of hydroxyurea in human plasma

Hydroxyurea: Analytical techniques and quantitative analysis

Hydroxyurea is a potent disease-modifying therapeutic agent with efficacy for the treatment of sickle cell anemia. When administered at once-daily oral doses that lead to mild marrow suppression, hydroxyurea leads to substantial and sustained fetal hemoglobin induction, which effectively inhibits erythrocyte sickling. When escalated to maximum tolerated dose, hydroxyurea has proven laboratory and clinical effects for both children and adults with sickle cell anemia. However, there is substantial inter-patient variability with regard to the optimal dosing regimen, as well as differences in treatment-related toxicities and responses that may be explained by hydroxyurea pharmacokinetics and pharmacogenetics. Addressing the safety and efficacy of hydroxyurea treatment requires quantitative and accurate drug analysis, and various laboratory techniques have been established. We review the historical and current analytical techniques for measuring hydroxyurea concentrations accurately, and discuss clinical settings where quantitative analysis can increase understanding and safety of this important therapeutic agent, and ultimately improve patient outcomes.

Isotope-dilution gas chromatography-mass spectrometry method for the analysis of hydroxyurea

BACKGROUND

Hydroxyurea is used in the treatment of various malignancies and sickle cell disease. There are limited studies on the pharmacokinetics of hydroxyurea, particularly in pediatric patients. An accurate, precise, and sensitive method is needed to support such studies and to monitor therapeutic adherence. We describe a novel gas chromatography-mass spectrometry (GC-MS) method for the determination of hydroxyurea concentration in plasma using stable labeled hydroxyurea C N2 as an internal standard.

METHODS

The method involved an organic extraction followed by the preparation of trimethylsilyl (TMS) derivatives of hydroxyurea for GC-MS selected ion-monitoring analysis. The following mass-to-charge (m/z) ratio ions for silated hydroxyurea and hydroxyurea C N2 were monitored: hydroxyurea-quantitative ion 277, qualifier ions 292 and 249; hydroxyurea C N2-quantitative ion 280, qualifier ion 295. This method was evaluated for reportable range, accuracy, within-run and between-run imprecisions, and limits of quantification.

RESULTS

The reportable range for the method was 0.1-100 mcg/mL. All results were accurate within an allowable error of 15%. Within-run and between-run imprecisions were <15%. Samples were stable for at least 4 hours at room temperature, 2 months at -20°C, and 6 months at -70°C, and after 3 freeze/thaw cycles. Extraction efficiency for 1-, 5-, 10-, and 50-mcg/mL samples averaged 2.2%, 1.8%, 1.6%, and 1.4%, respectively.

CONCLUSIONS

The isotope-dilution GC-MS method for analysis of hydroxyurea described here is accurate, sensitive, precise, and robust. Its characteristics make the method suitable for supporting pharmacokinetic studies and/or clinical therapeutic monitoring.

Analysis of anticancer drugs: a review

In the last decades, the number of patients receiving chemotherapy has considerably increased. Given the toxicity of cytotoxic agents to humans (not only for patients but also for healthcare professionals), the development of reliable analytical methods to analyse these compounds became necessary. From the discovery of new substances to patient administration, all pharmaceutical fields are concerned with the analysis of cytotoxic drugs. In this review, the use of methods to analyse cytotoxic agents in various matrices, such as pharmaceutical formulations and biological and environmental samples, is discussed. Thus, an overview of reported analytical methods for the determination of the most commonly used anticancer drugs is given.

Plasma hydroxyurea determined by gas chromatography-mass spectrometry

Hydroxyurea treatment is efficiently used to ameliorate the clinical course of patients affected with sickle cell disease. To understand the patient's wide variation in the clinical response to that drug and monitor its plasma levels, a new method was developed and validated. Fifty microL plasmatic samples containing hydroxyurea are added with internal standard, deproteinized, evaporated to dryness, silanized, and analyzed by gas chromatography-mass spectrometry, which operates in the selected ion mode after electron impact fragmentation. Linearity was found to extend to at least 100mg/L. Over a 1-25mg/L concentration range, coefficients of variation for intra-day and inter-day precision are 5.3% and 7.7%, respectively. Plasma blank-samples reveal endogenous hydroxyurea at a level <or=0.2mg/L. The performances of the method, which is fast and simple, encounter the analytical goals needed for evaluation of hydroxyurea treatment and for pharmacokinetic studies.

Quantitative analysis of trimethylsilyl derivative of hydroxyurea in plasma by gas chromatography–mass spectrometry

Hydroxyurea is an antitumor drug widely used in the treatment of sickle cell disease. The drug has been analyzed in biological fluids by a number of high-performance liquid chromatography (HPLC) methods. This paper describes a fast and highly reliable capillary gas chromatography-mass spectrometry (GC-MS) procedure that was developed for the detection and quantitation of hydroxyurea in plasma. The compound and its labeled internal standard were liquid extracted from plasma and derivatized with BSTFA before analysis. The detection limit of the assay was 0.078 microg/ml and the limit of quantitation was 0.313 microg/ml with linearity up to 500 microg/ml. Intra-day variation, as coefficient of variation (C.V., %) over the selected concentration range, was 0.3-8.7% and inter-day variation was 0.4-9.6%.

New isocratic high-performance liquid chromatographic procedure to assay the anti-sickling compound hydroxyurea in plasma with ultraviolet detection

A new procedure using high-performance liquid chromatography (HPLC) with ultraviolet detection to assay hydroxyurea (HU) levels in plasma has been developed. The drug was isolated from plasma by a direct deproteinization process with sulfosalicylic acid. Following neutralization of the acidic supernatant, an aliquot was loaded onto an Aminex HPX-72S column (300x7.8 mm). Chromatography was performed at 55 degrees C using a mobile phase consisting of acetonitrile-0.025 M ammonium sulfate buffer (pH 8.5) including 0.1% triethylamine, 0.01 M sodium sulfate, and 5 mM sodium heptane sulfonate. The UV absorbance of effluent was monitored at 214 nm. A flow-rate of 0.8 ml/min was used for analyzing HU in both human and mouse plasma. Under these conditions, the drug eluted at 12.6 min. The assay possessed linearity up to 425 microg/ml, with a lower limit of quantitation of 3.32+/-0.0004 microg/ml (mean+/-S.D., n=10). Intra-day and inter-day coefficients of variation were less than 8.5% and 8.7% respectively. Absolute differences were less than 7.4%. The method has been employed in clinical studies and the sensitivity of the assay was shown to be adequate for characterizing the plasma pharmacokinetics of HU in mice. In conclusion, the procedure described herein could be ideally suited for therapeutic monitoring of hydroxyurea.

Pharmacokinetics and pharmacodynamics of hydroxyurea

Hydroxyurea is used in the treatment of various forms of cancer, sickle-cell anaemia and HIV infection. Oral absorption of the drug is virtually complete, the volume of distribution is equivalent to total body water and elimination is through both renal and nonrenal mechanisms. Nonrenal elimination of hydroxyurea is characterised by Michaelis-Menten kinetics. Further studies are necessary to clarify several aspects of the pharmacokinetics and pharmacodynamics of hydroxyurea: the effect of age and disease state, concentration-effect relationship, the role of therapeutic drug monitoring, and the mechanisms of renal and nonrenal elimination. The recent development of improved assays for hydroxyurea should have benefits for future pharmacokinetic studies.

Colorimetric determination of hydroxyurea in human serum using high-performance liquid chromatography

A high-performance liquid chromatography assay for hydroxyurea in human serum was developed based on a commercial colorimetric assay kit for urea (Sigma Diagnostics). Serum (0.5 ml), spiked with methylurea as an internal standard, was treated with 70% perchloric acid. Supernatant (0.2 ml) was combined with 0.7 ml of BUN acid reagent and 0.6 ml of BUN color reagent. The resulting colored reactant (100 microl) was analyzed on a 300 x 3.9 mm Bondclone 10 C18 column coupled with a UV-Vis detector, at 449 nm. The mobile phase was 13% acetonitrile in water. Retention times of colored derivatives of hydroxyurea and methylurea were 6.5 and 12.2 min, respectively. The log-log calibration curve was linear from 0.0065 to 1.31 mM. Average accuracy was 99.9+/-4.0% and the intra- and inter-day error of assay did not exceed 11%.

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.

Pharmacokinetics of hydroxyurea in patients infected with human immunodeficiency virus type I

In a prospective, randomized, controlled, three-arm study, the pharmacokinetics of hydroxyurea administered as an antiviral agent in patients infected with human immunodeficiency virus type 1 (HIV-1) were evaluated. The three arms of the study consisted of azidothymidine (AZT) 250 mg twice daily, hydroxyurea 500 mg twice daily, or a combination of the two. Nine patients receiving hydroxyurea in monotherapy (n = 4) or in combination with AZT (n = 5) agreed to undergo multiple venipunctures for pharmacokinetic analysis. Sample collection was performed at steady-state conditions and serum concentration-time data for hydroxyurea were fitted using a one-compartment model. Mean (+/- standard deviation) peak concentration (Cmax) was 0.135 +/- 0.06 mmol/L and mean trough level (Cmin) was 0.0085 +/- 0.003 mmol/L. Mean concentration at steady state was 0.045 +/- 0.006 mmol/L. Apparent clearance (Cl/F) was 0.18 +/- 0.005 L/hr/kg, and half-life (t1/2) was 2.5 +/- 0.5 hours. Hydroxyurea given orally to patients infected with HIV-1 was well absorbed from the gastrointestinal tract, with a tmax of 0.85 to 0.96 hours after ingestion. Serum levels of hydroxyurea ranged from 0.01 to 0.13 mmol/L. These values are similar to the concentrations (between 0.01 and 0.1 mmol/L) demonstrated to inhibit HIV-1 in vitro. Our data show that hydroxyurea given at a dosage of 500 mg twice daily is sufficient to yield serum concentrations potentially useful for in vivo inhibition of HIV-1.