Pimobendan

Description

Pimobendan, a novel cardiotonic vasodilator, was introduced in Japan for the treatment of acute and mild to moderate chronic heart failure. It is a phosphodiesterase Ⅲ inhibitor and is able to enhance sensitization of myocardial contractile regulatory protein to calcium ions. The combination of these effects contribute to its inotropic activity. In patients with severe congestive heart failure, orally administered pimobendan improves cardiac index, stroke volume index, pulmonary wedge pressure, and systemic and pulmonary vascular resistance. Pimobendan is reported to be well tolerated and largely devoid of the proarrhythmic effects of classical phosphodiesterase Ill inhibitors. Studies also suggested that combination of the inotropic agent pimobendan with an ACE inhibitor such as enalapril may be superior to monotherapy for heart failure patients.

Chemical properties

White Solid

Originator

Boehringer lngelhelm (Germany)

The Uses of Pimobendan

Pimobendan is a cardiotonic agent. The study of the cardiotonic mechanism of Pimobendan using ventricular muscles from rabbits and guinea pigs suggests that Pimobendan acts by inhibiting phosphodiesterase III and potassium channel. The potent venodilating action of Pimobendan makes it a suitable treatment option for patients with congestive heart failure (CHF) as it also improves systemic vasoconstriction.

The Uses of Pimobendan

Pimobendan is a selective inhibitor of PDE3 with IC50 of 0.32 μM. It is a drug with both inotropic and vasodilatory properties that is used for the treatment of var-ious cardiac diseases.

Definition

ChEBI: Pimobendan is a pyridazinone and a member of benzimidazoles. It has a role as a cardiotonic drug, a vasodilator agent and an EC 3.1.4.* (phosphoric diester hydrolase) inhibitor.

brand name

Acardl

Biological Activity

Pimobendan is an inhibitor of phosphodiesterase 3 (PDE3; IC50 = 0.32 μM for guinea pig cardiac enzyme) that is selective for PDE3 over PDE1, PDE2, and PDE4 (IC50s = >30 μM). It is also a calcium sensitizer, decreasing the concentration of calcium required for half-maximal contractile force in isolated, skinned porcine ventricular fibers. Pimobendan increases the force of contraction in electrically-stimulated isolated guinea pig papillary muscles with an EC50 value of 6 μM, indicating positive inotropic effects. It increases survival time in dogs with congestive heart failure due to myxomatous mitral valve disease when administered in combination with angiotensin-converting enzyme inhibitors and furosemide . Formulations containing pimobendan have been used in the treatment of heart failure in dogs.

Biochem/physiol Actions

Pimobendan is an inotropic agent with a dual mechanism of action: it increases myocardial contractility by increasing calcium sensitization to troponin C and it promotes vasodilation by inhibiting phosphodiesterase III (PDE3). Pimobendan has been studied for treating heart failure and cardiomyopathy, primarily for veterinary uses.

Mechanism of action

The mechanism of mild mitral regurgitation (MR) in dogs treated with Pimobendan is a dual mechanism of action, which enhances myocardial contractility by increasing calcium sensitisation of troponin C and promotes vasodilatation by inhibiting PDEIII.

Side Effects

The most common side effects include gastrointestinal effects such as decreased appetite, and diarrhea. Other possible side effects include lethargy and difficulty breathing This short-acting medication should stop working within 24 hours, although effects can be longer in pets with liver or kidney disease.

Veterinary Drugs and Treatments

Pimobendan is used to treat dogs with congestive heart failure secondary to dilated cardiomyopathy or chronic mitral valve insufficiency (CMVI).

in vitro

In vitro, pimobendan was O-demethylated and subsequently O-glucuronidated. The rate of metabolism of pimobendan could be maintained in this culture system for > 3 weeks. However, the relative amount of a putative N-glucuronide under in vitro conditions was lower than in vivo[1].

References

[1] S A Pahernik. “Metabolism of pimobendan in long-term human hepatocyte culture: in vivo-in vitro comparison.” Xenobiotica 25 8 (1995): 811–23.