Comparison of hormonal and haemodynamic changes after long-term oral therapy with pimobendan or enalapril--a double-blind randomized study.

Twenty-four patients (one female, 23 male) with mild to moderate heart failure were randomly and double-blindly assigned to an oral treatment with 5 mg enalapril twice daily or 5 mg pimobendan (UDCG 115) twice daily. After the first tablet intake, blood pressure and heart rate were measured for 6 h. Therapy continued over 6 months. Systolic arterial blood pressure dropped from 126 +/- 20 mmHg to 111 +/- 14 mmHg (P less than 0.05) after the first enalapril tablet and from 123 +/- 16 mmHg to 112 +/- 13 mmHg (P less than 0.05) after the first pimobendan tablet. After 6 months, no important changes in blood pressure were observed in the pimobendan group and only a minor decrease in the enalapril group. There was no significant change in heart rate either after the first dose or after long-term therapy with either medication. After 6 months, cardiac index increased from 2.73 +/- 0.75 l.min-1.m-2 to 3.38 +/- 0.69 l.min-1.m-2 (P less than 0.01) after pimobendam, but did not change after enalapril (2.95 +/- 0.75 l.min-1.m-2 to 2.96 +/- 0.89 l.min-1.m-2, NS). Pulmonary capillary wedge pressure decreased during pimobendan long-term therapy from 16 +/- 8 mmHg to 14 +/- 8 mmHg (NS) and during enalapril from 21 +/- 7 to 14 +/- 7 mmHg (P less than 0.01). Exercise capacity increased in the pimobendan group from 17.2 +/- 5.4 kJ to 23.0 +/- 9.6 kJ (P less than 0.05), and in the enalapril group from 20.4 +/- 11.9 kJ to 24.8 +/- 18.5 kJ (NS) during long-term therapy over 6 months. Plasma renin activity increased from 0.96 to 3.6 ng.ml-1.h-1 (P less than 0.05) during enalapril long-term therapy, but remained unchanged (1.38 vs. 1.32 ng.ml-1.h-1, NS) during pimobendan. The new inotrope, pimobendan, exerted favourable long-term effects without haemodynamic or humoral signs of tolerance development.