Simultaneous Determination and Pharmacokinetics of Metolazone, Losartan and Losartan Carboxylic Acid in Rat Plasma by HPLC-ESI-MS-MS.

For the first time, we developed and validated a highly sensitive, selective and rapid HPLC-ESI-MS-MS method for simultaneous quantification of metolazone (MET), losartan (LOS) and its metabolite losartan carboxylic acid (LCA) in rat plasma. After solid-phase extraction, the analytes and internal standard (irbesartan) were extracted from 100 µL plasma sample on an Agilent Poroshell 120, EC-C18 (50 × 4.6 mm, i.d., 2.7 µm) column using 5 µL injection volume with a total run time of 3 min. Acidified methanol/water mixture was used as a mobile phase. The parent → product ion transitions for MET (m/z 366.0 → 258.9), LOS (m/z 423.2 → 207.0), LCA (m/z 437.0 → 235.1) and IS (m/z 429.2 → 207.0) were monitored on a triple quadrupole mass spectrometer, operating in the multiple reaction monitoring and positive ion mode. The method was found to be linear in the range of 0.05-250 for MET, 2-3,000 for LOS and 4-3,500 ng/mL for LCA. The method was validated with respect to selectivity, linearity, accuracy, precision, recovery and stability according to accepted regulatory guidelines. The described method was successfully applied to preclinical pharmacokinetic studies of analytes after an oral administration of mixture of MET (1 mg/kg) and LOS (10 mg/kg) in rats.

A rapid and sensitive determination of hypoxic radiosensitizer agent nimorazole in rat plasma by LC-MS/MS and its application to a pharmacokinetic study.

A highly sensitive, accurate and robust LC-MS/MS method was developed and validated for determination of nimorazole (NMZ) in rat plasma using metronidazole (MNZ) as internal standard (IS). The analyte and IS were extracted from plasma by precipitating protein with acetonitrile and were chromatographed using an Agilent Poroshell 120, EC-C18 column. The mobile phase was composed of a mixture of acetonitrile and 0.1 % formic acid (85:15 v/v). The total run time was 1.5 min and injection volume was 5 µL. Multiple reaction monitoring mode using the transitions of m/z 227.1 → m/z 114.0 for MNZ and m/z 172.10 → m/z 128.1 for IS were monitored on a triple quadrupole mass spectrometer, operating in positive ion mode. The calibration curve was linear in the range of 0.25-200 ng/mL (r(2) > 0.9996) and the lower limit of quantification was 0.25 ng/mL in the rat plasma samples. Recoveries of NMZ ranged between 88.05 and 95.25%. The precision (intra-day and inter-day) and accuracy of the quality control samples were 1.25-8.20% and -2.50-3.10, respectively. The analyte and IS were found to be stable during all sample storage and analysis procedures. The LC-MS/MS method described here was validated and successfully applied to pharmacokinetic study in rats.

Simultaneous Determination and Pharmacokinetic Study of Losartan, Losartan Carboxylic Acid, Ramipril, Ramiprilat, and Hydrochlorothiazide in Rat Plasma by a Liquid Chromatography/Tandem Mass Spectrometry Method.

The monitoring of the plasmatic concentrations of cardiovascular drugs is crucial for understanding their pharmacokinetics and pharmacodynamics. A simple, sensitive, specific, and high-throughput liquid chromatography/tandem mass spectrometry (LC-MS/MS) method was developed and validated for the simultaneous estimation and pharmacokinetic study of losartan (LOS), losartan carboxylic acid (LCA), ramipril (RAM), ramiprilate (RPT), and hydrochlorothiazide (HCZ) in rat plasma using irbesartan (IBS) and metolazone (MET) as internal standards (ISs). After solid phase extraction (SPE), analytes and ISs were separated on an Agilent Poroshell 120, EC-C18 (50 mm × 4.6 mm, i.d., 2.7 µm) column with a mobile phase consisting of methanol/water (85:15, v/v) containing 5 mmol/L ammonium formate and 0.1% formic acid at a flow rate of 0.4 mL/min. The precursor → product ion transitions for the analytes and ISs were monitored on a triple quadrupole mass spectrometer, operating in the multiple reaction monitoring (MRM) mode and switching the electrospray ionization (ESI) mode during chromatography from positive (to detect LOS, LCA, RAM, RPT, and IBS) to negative (to detect HCZ and MET). The method was validated as per the FDA guidelines and it exhibited sufficient specificity, accuracy, and precision. The method was found to be linear in the range of 3-3000 ng/mL for LOS and LCA, 0.1-200 ng/mL for RAM and RPT, and 1-1500 ng/mL for HCZ. The described method was successfully applied to the preclinical pharmacokinetic study of analytes after oral administration of a mixture of LOS (10 mg/kg), RAM (1 mg/kg), and HCZ (2.5 mg/kg) in rats.

Validated RP-HPLC Method for Simultaneous Quantitation of Losartan Potassium and Metolazone in Bulk Drug and Formulation.

A HPLC method has been described for simultaneous determination of Losartan potassium and Metolazone in formulation. This method is based on a HPLC separation of the two drugs on the Thermo Hypersil BDS-C(18) (250 mm × 4.6 mm, 5.0 µm) with isocratic conditions and a simple mobile phase containing acetonitrile:water (60:40) at a flow rate of 0.8 mL/min using UV detection at 237 nm. This method has been applied to a marketed formulation without interference of excipients. The linear regression analysis data for the calibration plots showed a good linear relationship over the concentration range of 2-12 µg/mL for Losartan potassium and 0.2-1.2 µg/mL for Metolazone, respectively. The method was validated for precision, robustness and recovery. Statistical analysis showed that the method is repeatable and selective for the estimation of Losartan potassium and Metolazone.