Acute and chronic effects of xamoterol in idiopathic dilated cardiomyopathy.

Xamoterol, a beta 1-partial agonist, was given to 10 patients with idiopathic dilated cardiomyopathy in NYHA functional classes II and III. The acute and chronic effects of xamoterol were assessed by changes in effort tolerance measured by multistage bicycle ergometry, echocardiography, radionuclide ventriculography and right heart catheterization. The acute effect was determined after a single intravenous injection of 0.2 mg/kg of xamoterol. Exercise heart rate decreased from 117 +/- 10 (mean +/- 1 SD) to 97 +/- 19 beats/min (p less than 0.01), but blood pressure and cardiac index were unaffected. When the drug was given orally at 200 mg/day for 3 months, exercise duration increased from 4.2 +/- 2.3 to 6.4 +/- 2.4 min (p less than 0.01), echocardiographic ventricular ejection fraction from 29 +/- 12 to 33 +/- 14% (NS) and radionuclide left ventricular ejection fraction from 37 +/- 11 to 45 +/- 14% (p less than 0.01), while pulmonary wedge pressure during exercise decreased from 40 +/- 10 to 31 +/- 10 mmHg (p less than 0.01). It may be concluded that xamoterol, by its action as a partial agonist, demonstrated both beta-agonist and antagonist effects in patients with idiopathic dilated cardiomyopathy. It thereby had beneficial effects on left ventricular function with resultant improvements in effort tolerance and subjective symptoms during long term treatment.