Simple ultrasensitive spectrofluorimetric method for determination of midodrine in its tablet form: Application to content uniformity testing.

A novel, simple, sensitive method was developed for determining midodrine spectrofluorimetrically in both its raw pure form and its tablet form. This study is based on the native fluorescence of midodrine and discusses the optimum solvent used and the wavelength range. The presented method was then validated with respect to linearity, accuracy, precision, and limits of detection and quantitation. The constructed calibration curve showed a linear range of 0.1-2.0 µg/ml. The limit of detection and limit of quantitation values were 0.03 and 0.10 µg/ml respectively. Finally, content uniformity testing was applied according to the United States Pharmacopoeia by adapting the presented method.

The convenient use of fluorescamine for spectrofluorimetric determination of midodrine hydrochloride in pure form and its tablets formulation: Application to content uniformity testing.

A novel sensitive and simple spectrofluorimetric method was developed then validated for determination of midodrine in both its authentic pure form and its tablets. This method is based on the reaction between midodrine's aliphatic primary amine moiety with fluorescamine reagent, using borate buffer at pH 7.8 and yielding a highly fluorescent product whose fluorescence intensity was measured at 462 nm after excitation at 388 nm. This method represents the first attempt for determination of midodrine spectrofluorimetrically. A calibration curve was constructed showing that the linear range was 0.2-3.0 µg/ml. The limit of detection and limit of quantitation values were 0.06 and 0.19 µg/ml respectively. The correlation coefficient (r) and the determination coefficient (r2 ) values were 0.9992 and 0.9984 respectively. The proposed method was validated according to ICH guidelines and successfully applied for determination of midodrine in its tablets with an overall % recovery of 99.56 ± 0.95. Finally, the presented method was adapted to study the content uniformity test according to United States Pharmacopeia guidelines.

Ion selective phosphotungestate and beta-cyclodextrin based membrane electrodes for stability-indicating determination of midodrine hydrochloride.

This paper reports the construction and evaluation of two ion selective electrodes for the determination midodrine hydrochloride (MD) by direct potentiometry in pure drug substance and in tablet formulations. Precipitation based technique was used for fabrication of the first membrane sensor (sensor 1) using phosphotungestate (PT) and dioctylphthalate (DOP) as cation exchanger and solvent mediator, respectively. beta-cyclodextrin (beta-CD)-based technique with PT as a fixed anionic site in PVC matrix was used for fabrication of the second membrane sensor (sensor 2). The proposed sensors showed fast, stable Nernstian responses of 54 and 56 mV/decade for sensors 1 and 2, respectively, across a relatively wide MD concentration range (1x 10(-4) to 1 x 10(-1) mol/L and 5 x 10(-5) to 1 x 10(-1) mol/L for sensor 1 and 2, respectively) in the pH range of 5-7. Sensor I and sensor 2 can be used for three and two weeks, respectively without any measurable change in sensitivity. The suggested electrodes succeeded to determine intact MD in the presence of up to 10% of its degradation product and displayed good selectivity in presence of common inorganic and organic species.

Development of a simple validated spectrofluorometric method for the assay of midodrine in tablets dosage form; Application to content uniformity testing.

A new sensitive spectrofluorimetric technique has been established for the estimation of midodrine hydrochloride. This method depends on the condensation reaction of ortho-phthalaldehyde with the primary aliphatic amine of midodrine in the presence of 2-mercapto-ethanol. The pH of the medium was adjusted to 9.0 using 0.1 M borate buffer. The fluorescence of the product was measured at wavelength of 451 nm after excitation at 334 nm. The method was rectilinear over a concentrations range of 0.1 to 1.5 µg mL-1. The lower detection and quantitation limits were 31 and 94 ng mL-1, respectively. The method was investigated following the guidelines of the International Council of Harmonization. Analysis of commercial tablet dosage form was carried out successfully by the current method with excellent recovery percentages and with no influence from coexisted pharmaceutical additives .This method was used to evaluate the uniformity of the contents of commercial tablets according to the United States Pharmacopoeia.

Stereoselective determination of midodrine and desglymidodrine in culture medium: application to a biotransformation study employing endophytic fungi.

A CE method was developed and validated for the stereoselective determination of midodrine and desglymidodrine in Czapek culture medium to be applied to a stereoselective biotransformation study employing endophytic fungi. The electrophoretic analyses were performed using an uncoated fused-silica capillary and 70 mmol/L sodium acetate buffer solution (pH 5.0) containing 30 mmol/L heptakis (2, 3, 6-tri-O-methyl)-beta-CD as running electrolyte. The applied voltage and temperature used were 15 kV and 15 degrees C, respectively. The UV detector was set at 200 nm. The sample preparation was carried out by liquid-liquid extraction using ethyl acetate as extractor solvent. The method was linear over the concentration range of 0.1-12 microg/mL for each enantiomer of midodrine and desglymidodrine (r> or =0.9975). Within-day and between-day precision and accuracy evaluated by RSDs and relative errors, respectively, were lower than 15% for all analytes. The method proved to be robust by a fractional factorial design evaluation. The validated method was used to assess the midodrine biotransformation to desglymidodrine by the fungus Phomopsis sp. (TD2), which biotransformed 1.1% of (-)-midodrine to (-)-desglymidodrine and 6.1% of (+)-midodrine to (+)-desglymidodrine.

A novel, sensitive and selective method of UPLC/MS-MS for rapid simultaneous determination of midodrine and its active metabolite desglymidodrine in human plasma: Application to support bioequivalence study in healthy human volunteers.

A specific, rapid, sensitive and selective ultra-performance liquid chromatography - tandem mass spectrometry has been developed for the simultaneous determination of midodrine and desglymidodrine in human plasma. The analytes and its deuterated analogs were quantitatively extracted from 100µL of human plasma by solid phase extraction technique. Separation of analytes was achieved on the Waters Acquity UPLC BEH C18 (50×2.1mm, 1.7µm) column using acetonitrile-4.0mM ammonium formate, pH 2.5(90:10, v/v) as mobile phase. The protonated analytes were quantified by selected reaction monitoring in the positive ionization mode by triple quadrupole mass spectrometer. The calibration plots were linear over the concentration range of 0.050-50.0ng/mL. The intra-batch and inter-batch precision (%CV) across quality control levels was <4.0 and the% mean relative recovery was ≥96%. Various other parameters like stability in different conditions; matrix effect and reproducibility of the method were performed in accordance with the guidelines specified by the USFDA for bioanalytical method development and validation. The developed method was successfully administered to the pharmacokinetics study of 5 mg midodrine tablet in 12 healthy subjects. Reproducibility of assay was proved by reanalysis of 48 incurred samples.

Human alpha1-glycoprotein acid as chiral selector in the enantioseparation of midodrine and deglymidodrine racemates by HPLC.

Human alpha1-acid glycoprotein (alpha1-AGP) has been used as a chiral stationary phase (CSP) for the enantioseparation of midodrine and deglymidodrine racemates in the same HPLC run. The imobilized AGP resulted as the best chiral selector for the enantioresolution of two compounds. Due to the modification of alpha1-AGP characters as a result of changing the composition of the mobile phase, an attempt study of the watery mobile phase (ionic strength and pH of the buffer, nature and concentration of the organic modifier) allowed for an increase in the enantioselectivity of the chromatographic system and an optimization of the resolution base-line of both enantiomeric pairs.

HPLC analysis of midodrine and desglymidodrine in culture medium: evaluation of static and shaken conditions on the biotransformation by fungi.

A high-performance liquid chromatography (HPLC) method is presented for the simultaneous determination of midodrine and desglymidodrine (DMAE) in Czapek-Dox culture medium, to be used in biotransformation studies by fungi. The HPLC analysis was conducted using a Lichrospher 100 RP18 column, acetonitrile-40 mmol/L formic acid solution (60:40, v/v) as mobile phase, and ultraviolet detection at 290 nm. The sample preparation was conducted by liquid-liquid extraction using ethyl acetate as extractor solvent. The method was linear over the concentration range of 0.4-40.0 µg/mL for midodrine (r ≥ 0.9997) and DMAE (r ≥ 0.9998). Within-day and between-day precision and accuracy were evaluated by relative standard deviations (≤ 8.2%) and relative errors (-7.3 to 7.4%), respectively. The validated method was used to assess midodrine biotransformation by the fungi Papulaspora immersa Hotson SS13, Botrytis cinerea UCA 992 and Botrytis cinerea 2100 under static and shaken conditions. Under shaken conditions, the biotransformation of midodrine to DMAE was more efficient for all studied fungi, especially for the fungus Botrytis cinerea 2100, which converted 42.2% of midodrine to DMAE.