title: Simultaneous determination of losartan, losartan acid and amlodipine in human plasma by LC-MS/MS and its application to a human pharmacokinetic study.
abstract: BACKGROUND
  A simple, rapid and sensitive liquid chromatography-tandem mass spectrometric assay method has been developed and fully validated for simultaneous quantification of losartan and its active metabolite, losartan carboxylic acid, and amlodipine in human plasma. Irbesartan was used as an internal standard.
  
  
  METHODS
  The analytes were extracted from human plasma samples by solid-phase extraction technique using Oasis HLB cartridges, (Waters Corporation, Mumbai, India). The reconstituted samples were chromatographed on a C18 column by using an 85:15, v/v mixture of methanol and 0.1% v/v formic acid as the mobile phase at a flow rate of 1.0 mL/min. A detailed validation of the method was performed as per the FDA guidelines.
  
  
  RESULTS
  The calibration curves obtained were linear (r ≥ 0.99) over the concentration range of 0.5-1000 ng/mL for losartan and for its active metabolite losartan acid and 0.05-10.1 ng/mL for amlodipine. The results of the intra- and inter-day precision and accuracy studies were well within the acceptable limits.
  
  
  CONCLUSIONS
  A run time of 2.5 min for each sample made it possible to analyze more than 300 plasma samples per day. The proposed method was found to be applicable to clinical studies.
authors.affiliation: University College of Pharmaceutical Sciences, Jawaharlal Nehru Technological University, Kukatpally, Hyderabad, Andhra Pradesh, India.
authors.forename: Vijaya Kumari
authors.initials: VK
authors.lastname: Karra
authors.forename: Nageswara Rao
authors.initials: NR
authors.lastname: Pilli
authors.forename: Jaswanth Kumar
authors.initials: JK
authors.lastname: Inamadugu
authors.forename: J V L N Seshagiri
authors.initials: JV
authors.lastname: Rao
keywords: Amlodipine; liquid chromatography-tandem mass spectrometric method; losartan; losartan acid; pharmacokinetics