An improved LC-MS/MS method for quantitative determination of metolazone in human plasma and its application to a pharmacokinetic study

Development and Validation of Two Robust Stability-Indicating Chromatographic Methods for Determination of Metolazone in Drug Substance and Pharmaceutical Dosage Form in the Presence of Its Degradation Products and Characterization of Main Degradation Products Based on LC-MS

Two robust and selective stability-indicating chromatographic methods were developed and validated for the determination of metolazone in drug substance and pharmaceutical dosage form in the presence of its degradation products. The HPLC method employed a Kromasil C18 (250 × 4.6,5 μm) column and a mobile phase of acetonitrile: 0.2% orthophosphoric acid (32:68 v/v) at a flow rate 2 mL/min and detection at 238 nm. The separation was performed in HPLC isocratic mode. The robustness of the suggested method was assessed using the Plackett-Burman design, parameters affecting system suitability were established and non-significant intervals for the significant parameters were considered. The HPTLC method employed Nano-SIL-20 UV254 HPTLC plates as adsorbent, ethyl acetate: toluene: acetic acid solution (4:4:0.5, v/v/v), as a developing solvent system and densitometric detection at 238 nm. Metolazone was exposed to different stress conditions, including acid and alkaline hydrolysis and oxidative and photolytic degradation. The main degradation products obtained have been characterized and interpreted based on LC-MS. The linearity of the suggested methods was proved in the concentration range of 20-75 μg/mL for the HPLC method and 100-900 ng/spot for the HPTLC method. The suggested methods were validated according to international conference on harmonization guidelines. These methods were successfully dedicated for the estimation of metolazone in drug substance and pharmaceutical dosage form in the presence of its degradation products. The results of the suggested methods were evaluated and compared statistically with results obtained by an official method without finding any significant difference.

Pharmacokinetic study of single- and multiple-dosing with metolazone tablets in healthy Chinese population

BACKGROUND

Metolazone is a diuretic, saluretic and antihypertensive chemical compound from the quinazoline category that possesses medicinal features similar to those of other thiazide diuretic drugs. However, the pharmacokinetics of metolazone in the Chinese population has rarely been studied. This study aimed to examine the pharmacokinetic characteristics, safety characteristic, and tolerability of metolazone in healthy Chinese subjects after single and multiple doses taken orally as well as the effects that food and gender have on oral metolazone pharmacokinetic parameters.

METHODS

An open-label, randomized, and single- and multiple-dosing investigation was performed in healthy Chinese subjects. The investigation included 3 study groups: the 0.5 mg, 1 mg and 2 mg dose groups were the single-dose study groups in the first stage. Eligible volunteers were randomly and orally administered a single 0.5 mg, 1 mg, or 2 mg metolazone tablet. The 0.5 mg dose group was also part of the multiple-dose study group, and the 1 mg dose group was the food-effect study group in the second stage. Human plasma samples were gathered pre-dosing and up to 48 h after dosing. The human plasma sample concentration of metolazone was quantified using a validated liquid chromatography tandem mass spectrometry method. Pharmacokinetic data were calculated by a noncompartmental analysis method using WinNonlin version 6.4. Tolerability was evaluated based on adverse events, medical examination, 12-lead ECG, and other clinical laboratory exams.

RESULTS

Thirty eligible subjects (15 men and 15 women) were registered in our investigation and completed all of the study stages. The AUC and C_max showed dose proportionality after a single dose based on the linear-regression analysis. A comparison of the pharmacokinetic data revealed that the differences between the male and female groups were not statistically significant. The t_max of metolazone was increased by approximately 100% in the fed condition. Metolazone was well tolerated at the tested dose, and no adverse effects were observed.

CONCLUSIONS

Single dosing with 0.5 mg, 1 mg, or 2 mg metolazone yielded linear plasma pharmacokinetic properties in healthy Chinese subjects. Multiple oral doses of metolazone did not display significantly different distributions or elimination characteristics from those observed for a single dose. Gender factors did not appear to influence the pharmacokinetic parameter variation of metolazone. The t_max of metolazone increased in the fed condition. Metolazone was well tolerated at the tested dose in this study.

TRIAL REGISTRATION

This investigation is retrospectively registered at chictr.org.cn (ChiCTR-IIR-17012929, October 09 2017).

Simultaneous determination of metolazone and valsartan in plasma by on-line SPE coupled with liquid chromatography/tandem mass spectrometry

Combination of metolazone (0.5 mg) and valsartan (80 mg) has been verified as a promising therapy treatment for hypertension. In order to facilitate to pharmacokinetic research, it needs a method for the simultaneously determination of metolazone and valsartan in biological samples. However, there are no relative reports so far. In order to facilitate to pharmacokinetic research, an on-line solid phase extraction coupled with liquid chromatography-tandem mass spectrometry method for the simultaneous determination of metolazone and valsartan in beagle dog plasma was developed and validated in this study. An on-line solid phase extraction column Retain PEP Javelin (10 mm × 2.1 mm) was used to remove impurities in plasma samples. The metolazone, valsartan and internal standard (losartan) were separated on a Poroshell 120 SB-C18 column (4.6 mm × 50 mm × 2.7 µm) with a gradient elution procedure. Acidified acetonitrile/water mixture was used as a mobile phase. The selected multiple-reaction monitoring mode in positive ion was performed and the parent to the product transitions m/z 366/259, m/z 436.2/291 and m/z 423.4/207 were used to measure the metolazone, valsartan and losartan. The method was linear over the range of 0.1-100 ng/mL and 1-1000 ng/mL for metolazone and valsartan, respectively. This method was validated in terms of specificity, linearity, sensitivity, precision, accuracy, matrix effect, and stability and then successfully applied to pharmacokinetic studies of the metolazone and valsartan combination tablets in beagle dogs.