Pimobendane

# Overview
Pimobendan (or pimobendane)(INN) is a veterinary medication manufactured by Boehringer Ingelheim under the trade names Vetmedin and Acardi (Japan). It is both a calcium sensitizer and a selective inhibitor of phosphodiesterase III (PDE3) with positive inotropic and vasodilator effects.
Pimobendan is used in the management of heart failure in dogs, most commonly caused by myxomatous mitral valve disease (also previously known as endocardiosis), or dilated cardiomyopathy. Research has shown that pimobendan increases survival time and improves quality of life in canine patients with congestive heart failure secondary to mitral valve disease when compared with benazepril, an angiotensin-converting-enzyme (ACE) inhibitor. Under the trade name Acardi, it is available for human use in Japan.

# Mechanism of action
Pimobendan is a positive inotrope (increases myocardial contractility). It sensitizes and increases the binding efficiency of cardiac troponin in the myofibril to the calcium ions that are already present in systole. In normal hearts it increases the consumption of oxygen and energy to the same degree as dobutamine but in diseased hearts it may not.  Pimobendan also causes peripheral vasodilation by inhibiting the function of phosphodiesterase III. This results in decreased resistance to blood flow through systemic arterioles, which decreases afterload (decreases the failing heart's workload) and reduces the amount of mitral regurgitation.

# Pharmacokinetics
Pimobendan is absorbed rapidly when given via the oral route and has a bioavailability of 60-65%. Bioavailability is markedly decreased when ingested with food. It is metabolized into an active metabolite (desmethylpimobendan) by the liver. The parent compound, pimobendan, is a potent calcium sensitizer while desmethylpimobendan is a more potent phosphodiesterase III inhibitor. The half-life of pimobendan in the blood is 0.4 hours and the half-life of its metabolite is 2 hours. Elimination is by excretion in the bile and then feces. Pimobendan is 9095% bound to plasma proteins in circulation. This may have implications in patients suffering from low blood protein levels (hypoproteinemia/hypoalbuminemia) and in patients that are on concurrent therapies that are also highly protein bound.

# Combinations
Pimobendan is often used in combination with three other drugs to palliate dogs with heart failure (pulmonary edema, pleural effusion, ascites). These are:
- Furosemide, a diuretic, to reduce edema and effusion.
- Spironolactone, an aldosterone antagonist. This has two actions, firstly, as a potassium-sparing diuretic, although its diuretic properties are small compared with those of furosemide. Secondly, it reduces aldosterone-mediated myocardial fibrosis, possibly slowing the progression of heart disease.
- An ACE inhibitor, often enalapril (trade name Enacard) or benazepril (Fortekor). These drugs inhibit the action of angiotensin-converting enzyme, producing a balanced vasodilation, along with other potentially favorable effects.
Other drugs may also be used as required to manage certain arrhythmias that are often associated with heart disease.

# Synthesis
Pimobendan can be synthesized beginning with anisoyl chloride.