Pimobendan (Vetmedin) is a heart medication that is becoming a frequently used drug for cats with heart disease. It is approved for use in the United States for dogs with congestive heart failure (CHF) caused by either dilated cardiomyopathy or mitral valve disease, but it is not licensed for use in cats and is considered controversial. It is used off-label in cats to treat congestive heart failure, especially in cases where the heart muscle is needed to contract more efficiently.
Congestive Heart Failure
Congestive heart failure is a disorder that occurs in both pets and in human beings. Over time, the valves of the heart become less effective; as a result, blood pumps more slowly and less efficiently. Pets can be born with congestive heart failure or develop the disorder over time as a result of age, lack of exercise, or poor diet.
Since it develops slowly, symptoms can be hard to spot. Your pet may be short of breath, easily tired, or anxious. Over time, other symptoms can include a swollen belly, fainting, or weight loss. To determine whether congestive heart failure is present, your vet may conduct tests including an EKG, chest X-rays, or an ultrasound.
If congestive heart failure is found, your vet will want to take action quickly. Treatment will usually include a change in your pet's diet, a recommendation for increased exercise, and medication.
How Pimobendan Works
Pimobendan works to improve the heart's function in two ways. It acts on the heart muscle itself to improve its ability to contract normally. This is referred to as an inotropic function. It also dilates the blood vessels throughout the rest of the body, which provides less resistance to blood flow and makes it easier for the heart to pump the blood to where it needs to go.
When Pimobendan Should Be Used
Most veterinarians prefer to administer pimobendan only to pets that are suffering from congestive heart failure. Some vets recommend giving the medication once heart disease is detected but before congestive heart failure has occurred. This use is still controversial and may or may not be effective in slowing the progress of the disease.
Some veterinarians have used it successfully on cats, but it is contraindicated in some common types of heart disease that are found in cats, such as hypertrophic cardiomyopathy.
When It Should Not Be Used
In addition to hypertrophic cardiomyopathy, pimobendan is contraindicated in aortic stenosis and other types of heart disease in which it is dangerous to increase the amount of blood that has to be pumped by the heart's ventricles.
Pimobendan should also be used with caution in animals with cardiac arrhythmias, especially if the arrhythmias are not well-controlled. If your cat is sensitive to the medication, it should not receive pimobendan.
Potential Side Effects
It is important to note that some adverse reactions may actually be due to heart disease rather than a result of giving the pimobendan.
Potential health hazards have been documented in cats taking pimobendan for heart disease, including sudden death. Other observed side effects of cats in this condition include:
- Lack of appetite
- Difficulty breathing
- Azotemia (an increase in nitrogen-based waste products in the bloodstream)
- Fluid build-up in the chest cavity
- Heart murmur
There is some concern that pimobendan may also increase the risk of arrhythmias. Since heart disease can cause arrhythmias as well, it is difficult to determine whether the arrhythmia is a direct result of the pimobendan or simply a manifestation of the cat's heart disease.