The side effects of pimobendan for dogs are something dog owners may be concerned about. When veterinarians prescribe medications, they often must weight out the pros and cons. If your dog was prescribed this medication, most likely your vet has determined that its benefits outweigh its known risks. However, not all dogs react to medications in the same way. There are several factors to keep into consideration. In this article, veterinarian Dr. Ivana Crnec talks about pimobendan and the side effects of pimobendan for dogs.
Pimobendan for Dogs
Pimobendan (generic name) also known as Vetmedin® (brand name), is a veterinary heart medication used for managing heart failure in dogs. This relatively new and unique drug is classified as calcium sensitizer and selective phosphodiesterase 3 inhibitor with positive inotropic and vasodilator effects.
Pimobendan is indicated for the treatment of: congestive heart failure (CHF) in dogs due to Dilated cardiomyopathy (DCM) and Degenerative mitral valve disease (DMVD).
Based on the severity, CHF can be classified into four stages:
- Stage A – includes high risk dogs with no structural abnormalities and murmur
- Stage B – includes dogs with structural abnormalities but no clinical signs of heart failure
- Stage C – includes dogs with both structural abnormalities and either current or previous clinical signs of heart failure
- Stage D – includes dogs with clinical signs of heart failure refractory to conventional treatment.
Dogs who are classified as stage C and stage D are candidates for initiating pimobendan treatment. Dogs that do not manifest clinical signs of heart failure should not be put on pimobendan.
Pimobendan is available on the market under the brand name Vetmedin®. It comes in the form of oblong and half-scored chewable tablets from 1.25, 2.5, 5.0 and 10 milligrams. There is also an intravenous preparation of the drug bit depending on the country, its availability is though limited. Vetmedin should be stored at room temperature and it should not be exposed to light and moisture.
How This Drug Works
Pimobendan’s effects can be classified in three groups: 1) Increased cardiac contractility: this drug increases the dog's heartbeat’s strength and efficiency thus improving its pumping action, 2) Vasodilatation: pimobendan opens up the blood vessels that carry blood to and from the heart, thus reducing the efforts the heart needs to do while pumping blood around the body, and 3) Anticoagulation: pimobendan prevents te formation of blood clots.
Pimobendan is a short-acting drug and its effects resolve within 24 hours of administration (it is excreted through the feces). However, the effects can last longer in dogs with kidney and liver issues.
The recommended and labeled dosage for pimobendan is 0.5mg per kilo every 12 hours. Initially, when a rapid onset of action is required, it is advisable to administer the tablets on an empty stomach. Later on, as the use becomes chronic, the tablets should be given with food. When received orally, pimobendan is rapidly absorbed and its peak effect takes place within 2 to 4 hours of administration. Consult with your vet for specific recommendations.
Crushing the tablets and mixing them with water to be used as oral suspension is not recommended because the drug’s stability and efficacy in suspension are not determined. If you miss giving a dose to your dog give it as soon as you remember. However, if the next scheduled dose is close, it is better to skip the missed dose. Giving two doses at once as compensation is against the recommendations.
If your vet prescribes pimobendan, do not forget to mention any medication your dog is already taking (including herbal therapies, vitamins and minerals).
Side Effects of Pimobendan in Dogs
The most commonly observed pimobendan side-effects include vomiting, diarrhea, loss of appetite, lethargy, fainting, weakness, poor coordination, breathing difficulties (coughing and wheezing) and tachycardia (rapid heart rate).
The side effects of pimobendan for dogs are not very common and luckily not life-threatening. However, pimobendan poisoning is a serious and potentially life-threatening condition. Pimobendan poisoning occurs as a result of: accidental overdose caused by the owner, giving the drug to the wrong (healthy) dog and keeping the drug within the dog’s reach.
There are two types of pimobendan poisoning: acute which happens if the dog ingests a large amount of the drug at once and chronic – if the dog ingests smaller amounts of the drug but on a regular basis.
The signs of pimobendan poisoning include:
- Allergic reaction (impaired breathing, hives)
- Dark stool (melena)
- Loss of appetite
- Weight loss
- Loss of movement coordination (ataxia)
- Increased breathing rate
- Increased thirst and urination frequency
- Urinary accidents
- Elevated heart rate
- Irregular pulse or weak pulse
- Heart murmur
- Low blood pressure
- Accumulation of fluids in the chest and abdomen
- Shaking and trembling
The effects of pimobendan can be decreased if the dog simultaneously receives calcium channel blockers (verapamil or diltiazem) or certain beta blockers (propranolol and atenolol).
Pimobendan is contraindicated for dogs with pericardial effusion (the buildup of extra fluid in the space around the heart) and ascites due to the effusion. Pimobendan should also not be used for treating conditions in which increased cardiac output is unnecessary (such as aortic stenosis and hypertrophic cardiomyopathy). This drug has been associated with arrhythmia so it is not recommended for dogs with pre-existing and uncontrolled arrhythmia.
The safety of pimobendan use in pregnant and nursing dogs and in puppies younger than 6 months of age has not been established. Pimobendan should not be used in allergic individuals. The use of pimobendan in dogs with serious metabolic conditions (such as diabetes) and congenital heart effects is not evaluated.
The Pros of Using Pimobendan for Dogs
The survival time of dogs with congestive heart failure due to atrioventricular disease treated with pimobendan is 415 days. On the other hand, dogs with the same condition treated with conventional cardiac drugs have a survival time of 218 days.
It is estimated that 74 percent of pimobendan treated dogs are free of clinical signs after 8 weeks of use. The efficiency rate of conventional drugs (such as ACE inhibitors) for the same time frame is only 29 percent.
Pimobendan lengthens the survival time of dogs with congestive heart failure while causing fewer adverse reactions and side effects than conventional drugs.
As with any other drug, the side-effects of pimobendan for dog are possible. Therefore, it is recommended to monitor your dog for at least few days after initiating pimobendan treatment. It goes without saying that you should keep the vial with pimobendan tablets out of your dog’s reach.
About the Author
Dr. Ivana Crnec is a graduate of the University Sv. Kliment Ohridski’s Faculty of Veterinary Medicine in Bitola, Republic of Macedonia.
She currently practices as a veterinarian in Bitola and is completing her postgraduate studies in the Pathology of Domestic Carnivores at the Faculty of Veterinary Medicine in Zagreb, Croatia.
Ivana’s research has been published in international journals, and she regularly attends international veterinary conferences.