Isocratic, simultaneous reversed-phase high-performance liquid chromatographic estimation of six drugs for combined hypertension therapy

We report an isocratic, HPLC procedure for assay of the orally administered hypertension drugs atenolol, amlodipine, nifedipine, nitrendipine, nimodipine and felodipine given in retention order] of which atenolol, an aryloxypropanolamine beta-blocker is administered with anyone of the other five dihydropyridine calcium channel blockers in combined hypertension therapy. The drugs were dissolved in methanol and 20 microliters of a mix of the drugs was injected onto a reverse phase JASCO-metaphase ODS (250 x 4.0 mm) 5 mu column. Any one of the six drugs could be used as the internal standard. The drugs were resolved by elution with a pH 4.5 equivolume mobile phase of acetonitrile-0.01 M KH2PO4, with pH adjustments done with H3PO4 (flow-rate 1.5 ml min-1). The column effluent was monitored at 250 nm. The detector response (peak height ratio) was linear in the dynamic range of 25-3200 ng ml-1 of these drugs, with the detection limits at approximately 15 ng ml-1. Full statistical evaluation of the data including linear regression (least-square fit) analysis was performed. The suggested procedure has the advantage that all the five dihydropyridine derivatives can be quantified alone or in formulation with atenolol.