DOBUTAMINE PHARMACOKINETICS DURING DOBUTAMINE STRESS ECHOCARDIOGRAPHY

Many patients fail to achieve target heart rate during dobutamine stre ss echocardiography (DSE). We evaluated the pharmacokinetics of dobuta mine during DSE to determine whether patients with an impaired chronot ropic response have higher races of dobutamine clearance and consequen tly relatively lower plasma dobutamine levels. Plasma dobutamine level s, heart rate, and left ventricular (LV) ejection fraction (EF) were m easured in 13 mole patients referred for DSE at baseline and at the en d of stepped 3-minute dobutamine infusions of 5, 10, 20, and 30 mu g/k g/min. Dobutamine levels increased with doses: 27 +/- 10, 111 +/- 17, 275 +/- 17, and 403 +/- 28 ng/ml (mean +/- SEM). There was no relation observed between the plasma dobutamine level achieved at the 30-mu g infusion dose and the increase in heart rate from baseline (r = 0.066; p = 0.83). Baseline LVEF and a measure of chronotropic beta responsiv ity were identified as independent predictors of dobutamine clearance, together accounting for 73% of the variance in dobutamine clearance. In conclusion, (1) there is a dose-dependent increase in plasma dobuta mine levels during DSE, (2) dobutamine clearance is positively related to baseline LVEF and is partially mediated by a beta-receptor mechani sm, and (3) an impaired chronotropic response during DSE is not due to failure to achieve a sufficiently high dobutamine level. We conclude that in patients who lack an adequate heart rate response during the e arly stages of DSE (e.g., up to 20 mu g/kg/min infusion), administrati on of atropine rather than progressively higher amounts of dobutamine may provide a more effective strategy to achieve target heart rate. (C ) 1997 by Excerpta Medica, Inc.