Enzyme linked immunosorbent assay for determination of amlodipine in plasma

Amlodipine is a calcium channel antagonist of the dihydropyridine group. It is effective for treating hypertension, chronic stable angina, and vasospa stic angina. However, it is difficult clinically to pinpoint the maximum do sage for antihypertensive activity of the drug without having parallel data on the plasma drug concentrations. The methods for assaying amlodipine are either gas chromatography with electron capture detector or liquid chromat ography coupled with tandem mass spectrometry (or with an electrochemical d etector), which needs tedious derivatization, and is expensive and time con suming. Therefore, in this study we developed an enzyme immunoassay for det ermining amlodipine in plasma. Anti-amlodipine antibodies were produced fol lowing immunization of bovine serum albumin-amlodipine conjugate. These spe cific antibodies were used in a competitive biotin-avidin-based enzyme-link ed immunosorbent assay to measure amlodipine in plasma. Biotin was linked t o the antibodies in order to enhance the sensitivity of the assay. The assa y was specific for the free form of amlodipine with a detection limit of 0. 1 ng/ml and the intra- and interassay coefficient of variation ranged from 1.6-10.2%. This immunoassay provides a sensitive, reliable, rapid, and accu rate method for determination of amlodipine in plasma, which can be used in therapeutic drug monitoring pharmacokinetic studies and pharmaceutical ana lysis. J. Clin. Lab. Anal. 15:47-53, 2001. (C) 2001 Wiley-Liss, Inc.