Abstract
A novel LC-ESI-MS, validated simultaneous method is described for losartan, its active metabolite—losartan carboxylic acid (LCA) and hydrochlorothiazide (HCTZ) using irbesartan, candesartan and hydroflumethiazide (HFMZ) as internal standards respectively. A simple solid-phase extraction technique, excellent chromatographic separation on a C18Discovery column (4.6 × 50 mm, 5μm) within 3 minutes, negative mode MRM transitions m/z 421.3/156.9, m/z 427.2/193.1, m/z 435.3/157.1, m/z 439.4/309.1, m/z 330.0/238.8, and m/z 439.0/309.2 for losartan, HCTZ, LCA, irbesartan, HFMZ, candesartan respectively with dynamic linearity range of 2.54 ng/mL to 1509.56 ng/mL for losartan, 3.27 ng/mL to 1946.38 ng/mL for LCA and 2.10 ng/mL to 410.40 ng/mL for HCTZ are unique results of this investigation. Pharmacokinetic parameters are evaluated from 60 fasting, healthy male volunteers administered with a fixed-dose oral tablet formulation of losartan potassium 100 mg and hydrochlorothiazide 25 mg tablet in a randomized, single dose, 4 way cross-over study involving 36 hrs post dose serial blood collection. Results by non compartmental pharmacokinetic analysis assessed for 90% CI (obtained by ANOVA) for Cmax-93.37%, 98.67%, 103.60%, AUC0-t -101.43%, 100.15%, 103.94% and AUC0-∞-101.73%, 98.76%,103.39% for losartan, LCA, and HCTZ respectively were well within the predefined range (80–125%) and therefore determined to be bioequivalent in terms of rate and extent of absorption.
ACKNOWLEDGEMENTS
The authors would like to thank Ranbaxy Laboratories Ltd. for giving permission to write this paper and to use in-house data.