LC–MS determination and relative bioavailability of doxazosin mesylate tablets in healthy Chinese male volunteers

Validated RP-HPLC method for quantification of doxazosin in human plasma: Application in a bioequivalence study

OBJECTIVES

The aim of the present study was to validate a simple, sensitive, HPLC method of analysis of doxazosin in human plasma with fluorescence detection.

METHODS

The validated method employed one-step direct protein precipitation with acetonitrile. Chromatographic separation was attained using a reverse-phase 250mm×4.6mm 5μ Hypersil® BDS C 18 column and the mobile phase consisted of 10mm sodium dihydrogen phosphate dihydrate (pH=3.0) and acetonitrile at a ratio of (65:35 v/v). The method was evaluated in terms of linearity, precision, accuracy, selectivity and stability as per standard guidelines. The total run time was about 4.5min which make this method suitable for high throughput analyses. This method was applied to the bioequivalence study of two doxazosin tablets in healthy human volunteers.

RESULTS

Good linear response was achieved over the range of 5.0-200ng/mL. The observed within- and between-day assay precision ranged from 0.64% to 14.73%; accuracy varied between 94.11% and 105%. The 90% confidence intervals for the ratio Cmax, and AUC 0-∞ of the test product over those of reference were within the acceptable range (0.8-1.25) for bioequivalence.

CONCLUSION

The developed method was simple and could be applied to therapeutic drug monitoring of doxazosin.

Highly sensitive spectrofluorimetric method for determination of doxazosin through derivatization with fluorescamine; Application to content uniformity testing

A highly sensitive, simple and selective spectrofluorimetric method has been developed and validated for determination of doxazosin mesylate in pure form, pharmaceutical formulations and human plasma. The method is based on the reaction between doxazosin mesylate and fluorescamine in Teorell buffer solution (pH 3) to give highly fluorescent derivative that can be measured at 489 nm using excitation wavelength of 385 nm. Different experimental parameters affecting the reaction were carefully studied and optimized. The calibration plot was constructed over the concentration range of 16-400 ng mL(-1) with quantitation limit of 14.3 ng mL(-1). The developed procedure was validated according to ICH guidelines and the results were satisfactory. The proposed method has been successfully applied to the analysis of the cited drug in its pharmaceutical preparations as well as for content uniformity testing. The results showed excellent agreement with the reported method with respect to precision and accuracy. In addition, the drug concentration was determined in the spiked human plasma by the suggested method with % recovery in the range of 96.2-98.3% (SD; 0.76-0.93, n=5).

Rayleigh light scattering detection of three α1-adrenoceptor antagonists coupled with high performance liquid chromatograph

Herein, a Rayleigh light-scattering (RLS) detection method combined with high performance liquid chromatograph (HPLC) without any post-column probe was developed for the separation and determination of three α₁-adrenoceptor antagonists. The quantitative analysis is benefiting from RLS signal enhancement upon addition of methanol which induced molecular aggregation to form an hydrophobic interface between aggregates and water that produce a sort of superficial enhanced scattering effect. A good chromatographic separation among the compounds was achieved using a Gemini 5u C₁₈ reversed phase column (250 mm × 4.6 mm; 4 μm) with a mobile phase consisting of methanol and ammonium acetate-formic acid buffer solution (25 mM; pH=3.0) at the flow rate of 0.7 mL min(-1). The RLS signal was monitored at λex=λem=354 nm. A limit of detection (LOD) of 0.065-0.70 μg L(-1) was reached and a linear range was found between peak height and concentration in the range of 0.75-15 μg L(-1) for doxazosin mesylate (DOX), 0.075-3.0 μg L(-1) for prazosin hydrochloride (PRH), and 0.25-5 μg L(-1) for terazosin hydrochloride (TEH), with linear regression coefficients all above 0.999. Recoveries from spiked urine samples were 88.4-99.0% which is within acceptable limits. The proposed method is convenient, reliable and sensitive which has been used successfully in human urine samples.

Determination of Alkyl Methanesulfonates in Doxazosin Mesylate by Gas Chromatography-mass Spectrometer

High sensitive rapid gas chromatography-mass spectrometry method for the determination of four carcinogenic alkyl methanesulfonates viz. methyl methanesulfonate, ethyl methanesulfonate, isopropyl methanesulfonate and n-butyl methanesulfonate in doxazosin mesylate has been presented by using selective ion monitoring mode. The optimum separation was achieved between methyl methanesulfonate, ethyl methanesulfonate, isopropyl methanesulfonate and n-butyl methanesulfonate on a DB-5 (30 m×0.32 mm×1.0 μm) capillary column under programming temperature. Acetonitrile, water and ammonia (90:9:1 v/v/v) mixture was used as diluent. Various factors involved in the gas chromatography-mass spectrometry method development are also presented. This method was validated as per International Conference on Harmonization guidelines. The limit of quantitation of methyl methanesulfonate, ethyl methanesulfonate, isopropyl methanesulfonate and n-butyl methanesulfonate is 6 ppm with respect to 30 mg/ml of doxazosin mesylate.

Determination of Doxazosin Mesylate in Tablets by RP-HPLC

A simple, precise and rapid RP-HPLC method was developed for the determination of doxazosin mesylate in pharmaceutical formulations. The method was carried out on a Chromolith RP-C₁₈ column using a mixture of potassium phosphate buffer and methanol (40:60 v/v) and detection was done at 251 nm. The linearity range was 1-5 μg/ml. The retention time of the drug was 3.8 min. The LOD and LOQ were found to be 0.1 μg/ml and 0.5 μg/ml, respectively.