Liquid chromatographic and ultraviolet spectrophotometric determination of bevantolol and hydrochlorothiazide in feeds

Separate assay methods have been developed for the 2 components of an 80 + 20 drug blend of bevantolol and hydrochlorothiazide (HCT) in admixtures with animal feed. Drug/diet admixtures are extracted with methanol for reverse phase ion-pair liquid chromatographic (LC) assay of bevantolol, and with acetonitrile for ultraviolet spectrophotometric assay of HCT. Bevantolol, a cardioselective beta blocker, is separated from soluble feed components with an RP-18 column, using methanol-water-acetic acid (60 + 40 + 1) containing 0. 005M octane-sulfonic acid, sodium salt, as ion-pairing reagent. HCT is determined spectrophotometrically in acetonitrile extracts, using a suitable blank extract as reference. Average recovery of HCT from an admixture of 0.5 mg blend/g diet is 94.5% +/- 4.3 RSD and at 2.0 mg/g, 101.5% +/- 3.5 RSD. Bevantolol recovery from the same admixtures is 101.8% +/- 2.7 RSD and 99.0% +/- 3.5 RSD, respectively, using the method as described.