Pimobendan

1.What is pimobendan?

Pimobendan is a PDE3 (phosphodiesterase III) inhibitor, which increases cardiac contractility while dilating arterioles. In the simplest terms, it helps to relax blood vessels, thus lowering blood pressure and helping the heart to pump blood properly.

Pimobendan is a drug commonly given to veterinary patients with heart failure. It’s usually used in dogs, but may occasionally be prescribed to cats. It’s one of the most useful and well-tested drugs for veterinary cardiac patients, and it has a good safety record.

2、How does pimobendan work?

Pimobendan causes the heart to pump more effectively. It does this because it sensitises the heart to the effects of calcium, one of the signals used by the heart when it’s contracting. The heart therefore relaxes and contracts more effectively. Pushing the blood around the body (this family of drugs are sometimes called “positive inotropes” because they help the heart push harder). 

It also works to cause the blood vessels to open – ‘vasodilate’ – which reduces the amount of pressure the heart has to pump against. With less pressure to push against, less blood flows backwards through leaky valves. Not only does this mean that more blood is moving in the right direction, it means there’s less stress on the heart.

3、What are the indications for pimobendan?

Primarily used to treat congestive heart failure (CHF) in dogs with dilated cardiomyopathy and degenerative valvular disease:

• Late-stage ACVIM B2-phase degenerative mitral valve disease
• Late-stage preclinical dilated cardiomyopathy
• Pulmonary arterial hypertension (pulmonary hypertension), especially in patients with active CHF
• Arrhythmogenic right ventricular cardiomyopathy with concurrent myocardial dysfunction
• Used off-label for CHF in cats secondary to various forms of myocardial disease.

4、What is the dosage and Administration for pimobendan?

Pimobendan is given orally in the form of a tablet. The drug should be administered to the pet on an empty stomach. The typical dosage for pimobendan is 0.2 to 0.6 mg/kg daily, which is then divided into two doses that are given 12 hours apart. For pimobendan to work as expected, it is important to give the medication exactly as prescribed by the veterinarian.

Pimobendan starts working within 1 to 2 hours, but the effects may not be noticeable. For this reason, lab tests may be required to determine the drug’s effectiveness.
    If you miss a dose, then give the next dose as soon as you remember to or, if it is close to the next scheduled dose, wait and resume with the next regularly scheduled dose. Do not administer a double dose to catch up on a missed dose. After administering pimobendan, be sure to wash your hands thoroughly.

5、What are the side effects of pimobendan?

Pimobendan is relatively safe as side effects are often considered rare and uncommon with the medication. However, it is not extremely uncommon for pets to experience gastrointestinal issues, such as diarrhea, after beginning the medication. Ensure your dog remains well-hydrated if they begin experiencing diarrhea at any time.

In some instances, your pet may begin to experience additional GI issues on top of diarrhea, such as a lack of appetite. General lethargy, weakness, and a lack of energy may also be noticeable for pets that are just starting pimobendan.

More serious side effects to watch for that may indicate the need for assistance from a veterinarian include:

• Rash or increased redness of the skin
• Difficulty breathing, increased wheezing
• Racing or abnormal heartbeat
• Fainting or collapsing
• Bruising or bleeding
• Distended or painful abdomen
• Yellowing of the gums or the whites of the eyes

If these pimobendan for dogs side effects appear after you begin administering the medication to your dog, call your veterinarian immediately.

6、What circumstances should pimobendan not be used?

Pimobendan is contraindicated in hypertrophic cardiomyopathy, allergic animals, and animals with hypertrophic cardiomyopathy, aortic stenosis, or any other condition where cardiac output cannot be enhanced due to functional or organic reasons.

Caution should be exercised when using pimobendan in animals with arrhythmias, especially if the arrhythmia is not well-controlled.

In addition, pimobendan should be used with caution in dogs under 6 months of age, dogs with congenital heart disease, diabetes, or other severe metabolic disorders, dogs used for breeding, and pregnant or lactating female dogs.

7、What drug interactions should be noted when using pimobendan?

Pimobendan is typically used in combination with three other drugs to alleviate heart failure in dogs (pulmonary edema, pleural effusion, ascites). These are:

• Furosemide, a diuretic that reduces edema and fluid accumulation.
• Spironolactone, an aldosterone antagonist. It has two effects: firstly, as a potassium-sparing diuretic, although its diuretic effect is smaller compared to furosemide. Secondly, it can reduce aldosterone-mediated myocardial fibrosis, potentially slowing the progression of heart disease.
• An ACE inhibitor, usually enalapril or benazepril. These drugs inhibit the action of angiotensin-converting enzyme, producing a balanced vasodilation and other potential beneficial effects.

Pets receiving pimobendan should exercise caution when using the following drugs: calcium channel blockers (verapamil and diltiazem) and beta-blockers (propranolol, atenolol). Be sure to inform your veterinarian of any medications your pet is taking (including vitamins, supplements, or herbal therapies).

8、Pharmacokinetics of Pimobendan.

Pimobendan is rapidly absorbed through oral administration, with a bioavailability of 60-65%. When taken with food, the bioavailability is significantly reduced. It undergoes hepatic metabolism to an active metabolite (desmethylpimobendan). The parent compound, pimobendan, is an effective calcium sensitizer, while desmethylpimobendan is a more potent phosphodiesterase III inhibitor. The half-life of pimobendan in the bloodstream is 0.4 hours, and the metabolite has a half-life of 2 hours. Elimination occurs through biliary excretion, followed by fecal excretion. Pimobendan binds to plasma proteins in circulation at a rate of 90-95%. This may have an impact on patients with low blood protein levels (hypoproteinemia/hypoalbuminemia) and those undergoing concurrent therapy with high-protein-binding agents.