HPLC micromethodfor amrinone and metabolites in patientsreceivingconcurrent cephalosporin therapy

Amrinone (AMR), a bipyridine derivative, is receiving increasing use in postoperative cardiac patients as an inotrope and vasodilator. The hemodynamic response to amrinone in adults is linearly related to A1’vLRconcentrations, warranting therapeutic drug monitoring. We report a rapid microsample HPLC method for monitoring AMR and its principal metabolites, N-acetyl (N-ac) and N-glycolyl (Ngly) AMR. Serum was precipitated with acetonitrile, and the supernatant fluid was then injected into a C8 narrow-bore column. The mobile phase consisted of a 0.1 mollL sodium phosphate buffer (pH 6) with a gradient of acetomtrile going from 50 to 100 mJJL of eluent. Detection with a diode-array detector (DAD) concurrently monitored the absorbances at 320 and 345 nm. Monitoring 320 tim allows optimal quantification of AMR, N-gly, and N-ac. Patients often receive concurrent cephalosporin therapy, which is detectable at 320 nm but not 345 tim. Because cephalosporins coelute with Al”.’IRor metabolites, monitoring at 345 tim allows separation of these antibiotics from AMR and metabolites while retaining a detection limit of 0.5 mg/L.