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 < 0·05) after the first enalapril tablet and from 123±16 mmHg to 112±13 mmHg ( P < 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 < 0·01) after pimobendan, 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 <0·01). Exercise capacity increased in the pimobendan group from 17·2±5·4 kJ to 23·0±9·6 kJ ( P < 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 < 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.