|The aim of this double-blind (double dummy) clinical trial was to compare efficacy and safety of a pimobendan monotherapy (0.5 mg/kg/day) with a benazepril (0.25-0.5 mg/kg/day) and a pimobendan-benazepril combination therapy over 4 weeks. Treatment (pimobendan verum/placebo) could be continued thereafter in combination with any licensed cardiologic treatment and data on longterm survival was generated. Overall a number of 116 dogs was involved of which 81 cases with dilated cardiomyopathy (DCM) and 24 cases with valvular insufficiency (VI) were suitable for evaluation. Group size at the first visit was 36, 35 and 34 animals for the pimobendan group, benazepril group and combination therapy group respectively. The study was performed at 9 centres in different European countries by experienced veterinary cardiologists. Examination of the animals included x-ray, ECG and echocardiography beside standard clinical examination. Primary parameter was NYHA-classification of heart failure adapted from the guidelines of the New York Heart Association.
During the 4-week study period 34 % of the animals in the benazepril group but only 11 % in the pimobendan group and 8 % in the combination group dropped out because of lack of efficacy or death. The number of dropouts was significantly different in favour of pimobendan and pimobendan-benazepril combination (p =< 0.05). The strong reduction in the benazepril group size due to the high numbers of `non-response` to therapy lead to biased results in the primary parameter NYHA-classification as these animals did not complete all three examinations in the 4-week period. At the final examination mean NYHA-classification was 2.3 in the pimobendan and in the benazepril group and 2.1 in the combination group. Statistical evaluation of this parameter could only show significant non-inferiority of pimobendan or combination therapy compared to benazepril. Superiority to benazepril could not be proven for pimobendan monotherapy and pimobendan combination therapy due to the bias in group size. The evaluation of the parameter `overall efficacy` gave strong evidence for a superiority of both pimobendan and combination therapy in comparison to benazepril (p =< 0.05) as in this parameter all dropouts due to lack of efficacy or death were included and classified as `therapy failure`. At the final visit mean overall efficacy score was 2.5 for pimobendan, 2.4 for the combination treatment but only 3.3 for benazepril.
Analysis of longterm survival time according to Kaplan-Meier revealed a mean survival time of 232 days for pimobendan verum treated patients but only 164 days for pimobendan placebo animals (p=0.0206). The median survival time was 217 days in the pimobendan group but only 42 days in the placebo group. Furthermore, the risk ratio for the occurrence of the event `death` in the pimobendan group was only 57.6 % in comparison to placebo. No clinically relevant differences were found concerning observed adverse events.
It is concluded that under the circumstances investigated pimobendan treatment is superior to benazepril monotherapy and that a combination therapy with benazepril was not associated with additional clinically relevant benefits in comparison to pimobendan monotherapy.
Prof. Dr. Christophe W. Lombard
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