Determination of plasma concentrations of losartan in patients by HPLC using solid phase extraction and UV detection

Purpose: To establish a HPLC assay for plasma losartan and its active metab olite EXP3174 to facilitate clinical pharmacokinetic studies. Methods: the HPLC system consisted of a 250 x :, mm i.d. C-18 reversed phase column prec eded by a 4 x 4 mm guard column, a UV detector set at 254 nm, and an integr ator. The mobile phase was a mixture of 0.01 M ammonium phosphate: acetonit rile: methanol (6:3:1) containing 0.02% sodium azide and 0.04% TEA, with pH adjusted to 3.2. The system was operated isocratically at ambient temperat ure at a flow rate of 0.3 ml/min. Losartan and its active metabolite EXP317 4 were extracted from plasma using C-2 bonded silica gel standard solid pha se extraction. Results: recoveries of losartan and EXP3174 from plasma were greater than 70%. Using 0.5 mi of plasma sample, standard curves were line ar from 10 to 300 ng/ml (r(2) = 0.996 and 0.997 for losartan and EXP 3174, respectively). Sensitivity of the assay was < 10 ng/ml. Intra-and inter-ass ay variations were < 10 and 15%, respectively. The assay has been successfu lly applied to measuring plasma concentrations of losartan and EXP3174 in p atients receiving a daily dose of losartan (50-100 mg). Conclusion: The HPL C assay has adequate sensitivity, reproducibility, and specificity for clin ical pharmacokinetic studies. (C) 2000 Elsevier Science B.V. All rights res erved.