A dose response study with oral prenalterol in patients with chronic congestive cardiac failure.

Prenalterol is an orally active cardioselective beta agonist, with a long half-life. Previous studies have confirmed its inotropic activity following intravenous infusion in patients with heart failure. It has little chronotropic activity and no significant arrhythmogenicity. We have studied the response to sustained-release oral prenalterol given over four weeks at doses of 20, 40, 100, and 200 mg daily in 10 patients with New York Heart Association class II and III heart failure due to ischemic heart disease. All were in sinus rhythm and already receiving diuretics and digoxin. The drug was well tolerated and without side effects. Nine patients showed a dose-related improvement in their exercise tolerance as measured on the treadmill, up to a dose of 100 mg daily, with a significant increase in estimated oxygen uptake. There was a dose-related reduction in maximum heart rate, systolic blood pressure, and rate-pressure product during exercise, which is suggestive of a reduction in myocardial oxygen consumption. We conclude that prenalterol improves exercise tolerance without any significant cardiovascular or other side effects, and produces a clinically relevant and sustained improvement in patients with chronic heart failure. M-mode echocardiographic measurements of left ventricular dimension and function at rest did not show any change during the study.