Method Validation for Simultaneous Quantification of Olmesartan and Hydrochlorothiazide in Human Plasma Using LC-MS/MS and Its Application Through Bioequivalence Study in Healthy Volunteers

Abstract

A new, simple, sensitive, selective, rapid, and high-throughput liquid chromatography-tandem mass spectrometry (LC-MS/MS) method has been developed and validated for simultaneous quantification of Olmesartan and hydrochlorothiazide in human plasma. Simple liquid-liquid extraction procedure was applied for plasma sample pretreatment using a mixture of diethyl ether and dichloromethane, as an extraction solution. Analytes were separated on UNISOL C18 150*4.6 mm, 5 µm column using methanol, and 2 mM ammonium acetate pH 5.5 (80:20, v/v) as a mobile phase and detected by electrospray ionization in the multiple reaction monitoring (MRM) mode. The mass transition ion pairs were followed in negative ion mode as m/z 445.20 → 148.90 for Olmesartan; m/z 451.40 → 154.30 for Olmesartan D₆ and m/z 295.80 → 205.10 for hydrochlorothiazide; m/z 298.90 → 206.30 for hydrochlorothiazide ¹³C D₂. The method showed excellent linearity (r ² > 0.99) over the concentration range of 5.002-2,599.934 ng/ml for Olmesartan and from 3.005 to 499.994 ng/ml for hydrochlorothiazide. Precision (% CV) and accuracy (% bias) for Olmesartan were found in the range of 3.07-9.02% and -5.00-0.00%, respectively. Precision (% CV) and accuracy (% bias) for hydrochlorothiazide were found in the range of 3.32-8.21% and 1.99-3.80%, respectively. This as developed novel and high-throughput liquid-liquid extraction bioanalytical method has substantial innovative value with the benefits of cost effectiveness, good extraction efficiency, shorter analysis run time, low organic solvent consumption, and simpler procedure over the previously reported solid-phase extraction method. The application of this method in pharmacokinetic studies was further demonstrated successfully through a bioequivalence study conducted on healthy human subjects, following oral administration of combined formulation of Olmesartan medoxomil and hydrochlorothiazide in fixed-dose tablet.

Keywords: LC-MS/MS; bioequivalence; hydrochlorothiazide; hypertension; olmesartan; pharmacokinetics.

Figure 1

(A) Molecular structure of Olmesartan (OLM) OLM with parent ion scan m/z 445.2 amu and (B) product ion scan m/z 148.9 amu; (C) Molecular structure of hydrochlorothiazide (HCTZ) with parent ion scan m/z 295.8 amu, (D) product ion scan m/z 205.1 amu.

Figure 2

Chromatograms of OLM for (A) blank, (B) LLOQ (lower limit of quantification), (C) upper limit of quantification (ULOQ); and chromatograms of HCTZ for (D) blank, (E) LLOQ, (F) ULOQ.

Figure 3

Mean plasma concentration vs. time curve for OLM after administration of single dose of test and reference tablets.

Figure 4

Mean plasma concentration vs. time curve for HCTZ after administration of single dose of test and reference tablets.