Pimobendan

Contrasting Effects of Inhibition of Phosphodiesterase 3 and 5 on Cardiac Function and Interstitial Fibrosis in Rats With Isoproterenol-Induced Cardiac Dysfunction

Myocardial relaxation and stiffness are influenced by fibrillar collagen content. Cyclic nucleotide signaling regulators have been investigated targeting more effective modulation of collagen deposition during myocardial healing process. To assess the effects of phosphodiesterase type 3 and phosphodiesterase type 5 inhibitors on cardiac function and left ventricular myocardial fibrosis in catecholamine-induced myocardial injury, sildenafil and pimobendan were administered to male Wistar rats 24 hours after isoproterenol injection. Echocardiography and electrocardiogram were performed to assess kinetic and rhythm changes during 45 days of drug administration. At the end of study, type I and type III collagen were measured through immunohistochemistry analysis, and left ventricular pressure was assessed through invasive method. Echocardiography assessment showed increased relative wall thickness at 45 days in pimobendan group with significant diastolic dysfunction and increased collagen I deposition compared with nontreated positive group (3.03 ± 0.31 vs. 2.73 ± 0.28%, P < 0.05). Diastolic pressure correlated positively with type I collagen (r = 0.54, P < 0.05). Type III collagen analysis did not demonstrate difference among the groups. Sildenafil administration attenuated type I collagen deposition (2.15 ± 0.51 vs. positive group, P < 0.05) and suggested to be related to arrhythmic events. Arrhythmic events were not related to the quantity of fibrillar collagen deposition. Although negative modulation of collagen synthesis through cyclic nucleotides signaling have shown promising results, in this study, pimobendan postconditioning resulted in increased collagen type I formation and severe diastolic dysfunction while sildenafil postconditioning reduced collagen type I deposition and attenuated diastolic dysfunction.

A review of the pharmacology and clinical uses of pimobendan

OBJECTIVE

To review the pharmacology, research developments, and clinical uses of pimobendan

DATA SOURCES

Original research articles and clinical studies from 1984 to August 2011.

VETERINARY DATA SYNTHESIS

Pimobendan is approved for use in dogs for the treatment of congestive heart failure (CHF) secondary to chronic valvular heart disease (CVHD) and dilated cardiomyopathy (DCM). Expert-based veterinary guidelines recommend the use of pimobendan in the management of acute, hospital-based therapy for patients with CHF attributable to CVHD.

CONCLUSIONS

The use of pimobendan, an inodilator with phosphodiesterase 3 (PDE3) inhibitory and calcium-sensitizing properties, is regarded as a component of the standard of care in the management of dogs with CHF secondary to both DCM and CVHD. Further studies are warranted to confirm the safety and efficacy of pimobendan for the off-label use of this drug in asymptomatic CVHD, pulmonary arterial hypertension, asymptomatic myocardial diseases, CHF from all other causes and in cats with CHF.

Comparative cardiac toxicity of the i.v. administered benzimidazole pyridazinon derivative Pimobendan and its enantiomers in female Beagle dogs

The new positive-inotropic and vasodilatating drug Pimobendan (racemate), 4,5-dihydro-6-[2-(4-methoxyphenyl)-1H-benzimidazole-5-yl]-5-methyl-3 (2-H)-pyridazinone, and its enantiomers were investigated with regard to their cardiotoxicity in young adult female Chbb: Beagle dogs. The racemate and the (-)-isomer (eutomer) were intravenously injected once daily for 4 consecutive weeks at doses of 0.25, 0.75 and 2.25 mg/kg, and the (+)-isomer (distomer) at doses of 0.75, 2.25 and 6.75 mg/kg, respectively. Clinical signs, hematological, clinico-chemical, ophthalmologic and electrophysiological parameters were monitored. Plasma concentration-time profiles of the parent compound and the major metabolite UD-CG 212 were established on day 1 and in week 4 using an HPLC assay. Partial areas under the curves from 0.08 h to 1 h (AUC0.08-1 h) as well as the plasma concentration at time point 0.5 h/C0.5 h) were used for statistical calculations. Necropsy and histopathologic examination were performed after completion of the treatment period. Reduction of the blood pressure occurred already at low dosages of the racemate and the eutomer, but only in high dose distomer-treated animals. A tendency to tachycardia developed only in high dose females receiving the racemate. Consequently, with respect to the pharmacological effects and the adverse events, the racemate is equivalent to the eutomer. Plasma concentrations of parent compound and metabolite were dose-linear for racemate, eutomer and distomer within the dose range 0.25-2.25 mg/kg.d at both time points. There were no significant effects of form or repeated administration. A moderate increase of AUC0.08 1 h and C0.5 h could be seen on day 23 for the distomer indicating a stereoselektive metabolism of the latter. Histologic changes of the valvular and parietal endocardium being termed jet lesion were observed after administration of the racemate (> or = 0.75 mg/kg.d) and the eutomer (> or = 0.25 mg/kg.d) at distinctly lower doses than after the distomer (> or = 2.25 mg/kg.d). Furthermore, extent and severity of the morphologic lesions were found to be higher in dogs exposed to the racemate or the eutomer than in those receiving the distomer. The results gave evidence that the so-called cardiotoxicity by Pimobendan in dogs resulted from the exaggerated pharmacodynamic effect but not from the chemical nature of the compound per se. They corroborate also the previously raised assumption that the exaggerated pharmacodynamic activity of cardiotonic compounds in the broadest sense accounts for their morphologic adverse effects in experimental animals.

A quantitative comparison of functional and anti-ischaemic effects of the phosphodiesterase-inhibitors, amrinone, milrinone and levosimendan in rabbit isolated hearts

1. The functional and anti-ischaemic effects of the phosphodiesterase (PDE)-inhibitors, amrinone, milrinone and levosimendan, a new agent combining PDE-inhibitory with calcium-sensitizing properties, were investigated in rabbit isolated hearts (Langendorff, constant pressure: 70 cmH2O, Tyrode solution, Ca2+ 1.8 mmol l-1, 37 degrees C). Anti-ischaemic effects were studied in electrically-driven hearts (200 beats min-1). Acute regional ischaemia was induced by ligature of a branch of the circumflex coronary artery and quantified from epicardial NADH-fluorescence photography. 2. Cumulative concentration-response curves in spontaneously beating hearts in the presence of isoprenaline (10(-10) M), showed a higher inotropic and coronary vasodilator potency for levosimendan (EC50: 7 x 10(-7) M) compared to milrinone (EC50: 7.7 x 10(-6) M) or amrinone (EC50: 2 x 10(-5) M). Although the maximal coronary dilator activity was similar for the three agents, the maximal inotropic and chronotropic effects were lower for levosimendan than for amrinone or milrinone (P < 0.05). 3. In regionally ischaemic hearts, milrinone (10(-5) M) or levosimendan (5 x 10(-6) M) similarly enhanced the left ventricular pressure (+15-20%) (P < 0.05) and the global coronary flow (+40-50%) (P < 0.05). The epicardial NADH-fluorescence area was significantly diminished by milrinone or levosimendan (-20-30%) (P < 0.05) and there was no significant difference between the anti-ischaemic effects of either agent (P > 0.05). 4. It is concluded that amrinone and milrinone possess similar functional profiles in rabbit isolated hearts and a higher inotropic and chronotropic efficacy than levosimendan. At functionally equieffective concentrations, milrinone and levosimendan show similar anti-ischaemic effects, related to an improvement of myocardial perfusion. The calcium-sensitizing properties seem not to be relevant for cardioprotection by levosimendan at the concentration used.

Functional and antiischaemic effects of the phosphodiesterase inhibitor levosimendan in isolated rabbit hearts

Several phosphodiesterase inhibitors have been reported to possess antiischaemic properties by improving myocardial oxygen demand/supply balance. Levosimendan is a new phosphodiesterase inhibitor with calcium-sensitizing properties. We investigated the functional and antiischaemic properties of levosimendan in isolated electrically-driven rabbit hearts (Langendorff, constant perfusion pressure: 70 cm H2O, Tyrode solution, Ca++ 1.8 mmol/l, 37 degrees, 200 beats/min.). Acute regional myocardial ischaemia was induced by ligature of a circumflex artery branch and quantified from epicardial NADH-fluorescence photography.

RESULTS

The left ventricular pressure was similarly enhanced by levosimendan 10(-7) M or 5 x 10(-6) M (+15%) (P < 0.05). The global coronary flow was increased more markedly by levosimendan 5 x 10(-6) M (+35-50%) compared to 10(-7) M (+25%) (P < 0.05). The relative coronary flow (= global coronary flow/pressure-rate-product) was significantly enhanced only by levosimendan 5 x 10(-6) M (+20-35%) (P < 0.05), but not by levosimendan 10(-7) M (+10-15%) (P > 0.05). Epicardial NADH-fluorescence area and intensity were significantly diminished by levosimendan (-20%) (P < 0.05), and there was no significant difference between myocardial ischaemia reduction by levosimendan 10(-7) M and 5 x 10(-6) M (P > 0.05).

CONCLUSION

Levosimendan is an inotrope with coronary dilator activity, showing antiischaemic effects in isolated rabbit hearts. These may be caused by (1) phosphodiesterase-inhibition and improvement of myocardial perfusion and/or (2) by oxygen-sparing effects, related to calcium sensitization of myofilaments, particularly at lower concentrations associated with a lower coronary dilator activity.

Intractable heart failure despite angiotensin-converting enzyme inhibitors, digoxin, and diuretics: long-term effectiveness of add-on therapy with pimobendan

In 25 patients whose chronic congestive heart failure (CHF) had recently worsened to New York Heart Association class IV, pimobendan (5 to 20 mg/day) was added to maximum conventional therapy consisting of digoxin, diuretics, angiotensin-converting enzyme inhibitors, coumadin derivatives to prevent thromboembolic complications, and amiodarone to suppress serious ventricular rhythm disturbances. CHF was fatal in less than 1 month in five patients (two had shown some initial improvement). The other 20 had sustained improvement by at least one functional class, interrupted by episodes of CHF that usually responded to intravenous therapy. Median survival was 12 months (range 10 days to greater than 3 years); five patients died suddenly, 12 died of intractable CHF, and two died of other causes. Six patients were alive 3 years after the onset of treatment with pimobendan. Add-on therapy with pimobendan produced a sustained improvement in many patients with severe CHF that was no longer responding to a combination of digoxin, diuretics, and angiotensin-converting enzyme inhibitors.