Updated June 14, 2023
If you have a small dog, there’s a good chance they’ll end up being treated with pimobendan. Often sold as Vetmedin® or Cardisure®, it’s the most common treatment for a very common condition: heart disease in dogs.
One disease in particular, myxomatous mitral valve disease (MMVD) is said to account for 75% of heart disease and affects 85% of small dogs over 13 years old. Not all of these will need treatment, but many will. Later I’ll show you how to tell.
There is no question that recent advances have made MMVD much less of a death sentence than it once was. So it’s good to get to know pimobendan, the newest, and most commonly used of these treatments.
How Pimobendan Works
Pimobendan is a drug that unusually has two separate positive effects. First, it increases the strength of contraction of the heart, increasing the amount of blood delivered. Second, it dilates blood vessels in the general circulation, reducing the heart’s workload.
Pimobendan needs to be given at a dose of 0.2–0.3 mg/kg twice a day on an empty stomach, leading to the following inescapable logic. If it needs to be given one hour before any food and 12 hours apart, then even starting with a 7am dose will result in an 8pm dinner time. Now of course, we don’t recommend feeding dogs after dark…
You can picture the disappointment in peoples’ faces when they think this through. It’s definitely a drug for the early risers in the house. The only other alternative is to make their main meal in the morning.
Lifespan Of Dogs On Pimobendan
Early work demonstrated that pimobendan could help dogs with MMVD, but by how much was uncertain, and so vets like me were slow to change treatments that were already working. Then two large international studies appeared. With them came a sea-change in how we viewed this drug.
Each of them has something important to say about both effects and side effects. Both are referenced below.
2008: The QUEST Study
252 dogs with naturally occurring MMVD and congestive heart failure were divided into two groups: one taking pimobendan and another taking benazepril, the leading heart treatment at the time. Both were allowed other treatments as needed. They were then studied over the following years until one of the following three things happened:
- sudden death
- euthanasia for cardiac reasons
- treatment failure
For pimobendan, the median time to this endpoint was 188 days. For benazepril it was 140. So a good result, but far from impressive. However, it’s worth pointing out here that these survival times are artificially short; many dogs in the study had already been affected for some time before beginning.
Real life is better. The point is more that in matched groups, pimobendan outperformed its rival.
2016: The EPIC Study
To my knowledge, the EPIC study was the first in veterinary medicine to be stopped early because of what was found. 354 dogs were chosen who had MMVD but were not yet in heart failure. At this earlier stage they had enlarged hearts as determined by xray and ultrasound.
Up to the time of the study, treatment was not believed to help at this stage, and so they were divided into dogs given pimobendan and dogs given a harmless placebo instead. This time the endpoint was chosen to be one of:
- development of left-sided heart failure
- euthanasia for a cardiac reason
- death presumed to be cardiac in origin
The median time to this endpoint was 1228 days in the pimobendan group and 766 days in the placebo group. In other words, dogs with enlarged hearts but without heart failure had an extra 60% or 462 days of disease-free life if they took pimobendan.
This of course was a stunning result. Once it became obvious, all of the dogs were put on pimobendan.
Pimobendan Side Effects
Similar rates of adverse effects were reported for pimobendan and benazepril. This suggests that the drug is at least as safe as other heart treatments,
Pimobendan also recorded similar side effects to the placebo. Deaths in the pimobendan group were 46.4% versus 57.2% in the placebo group. This suggests that pimobendan is safe compared with any drug.
If you want to take a closer look, I’ve included the reported side effects from both studies in two tables after the references.
Help! Pimobendan Killed My Dog!
What then do we make of online reports of terrible events after dogs took pimobendan? The high rates of death and side effects in the placebo group provide the best clue. These are old dogs with a high risk of illness from any cause.
We humans are notoriously bad at separating causation from correlation. In fact, with any one dog, it’s virtually impossible to decide if a sudden death is caused by a drug or not. It’s only by looking at large groups that we can see the trend. Sometimes it’s real, other times it’s not.
Pimobendan may in fact cause deaths in some dogs. Even if so, the evidence tells us that they are heavily outweighed by the dogs that survive for longer.
When Should My Dog Take Pimobendan?
Pimobendan is a much better drug at stopping dogs going into heart failure than it is in treating them once they do. So here’s a quick summary of how to use pimobendan in 2022 and beyond:
- Get regular checkups (at least annually) to look for early signs of heart disease. This is mainly the appearance of a heart murmur.
- Once a murmur appears, watch fitness, coughing and resting respiratory rate closely and get a checkup at least every 6 months.
- Follow your vet’s advice on further testing. Sooner rather than later they will want to do chest xrays and possibly cardiac ultrasound to look for the signs of heart enlargement.
- Even if things are normal, expect things to change and so repeat the tests every 6 to 12 months based on your vet’s advice. Eventually you’re likely to spot the right time to start pimobendan.
- Once started, most heart disease will stabilise but dose adjustments and extra medications will still be necessary as the disease slowly worsens (hopefully over years, not months). Therefore, keep attending scheduled checkups and get advice straight away if anything changes.
Most importantly, trust the science. It’s very hard to judge the efficacy of any treatment used to prevent a disease instead of treat it, but we actually have a lot to go on here.
Related: A Dog With Dilated Cardiomyopathy (also treated with pimobendan) caused by a grain-free diet
Update: Mitral Valve Repair
I hesitate to add this as I fear giving dog owners false hope, but several comments below have spurred me to also discuss the surgical option. As of 2023, there are now several centres around the world that offer open heart surgery to improve mitral valve function. It is not replacement of the valve, but instead modifying its shape or adding support so that the leak is less significant.
Costs are extreme (I would guess $40-50K) and availability currently limited to the UK, France, Japan and the USA. If you Google ‘dog mitral valve repair’ you should find useful information from these sites. There is no doubt that this procedure will become more commonplace with time, and hopefully more realistic.
Have something to add? Comments (if open) will appear within 24 hours.
By Andrew Spanner BVSc(Hons) MVetStud, a vet in Adelaide, Australia. Meet his team here.
References
Boswood, A., Häggström, J., Gordon, S. G., Wess, G., Stepien, R. L., Oyama, M. A., … & Watson, P. (2016). Effect of pimobendan in dogs with preclinical myxomatous mitral valve disease and cardiomegaly: the EPIC study—a randomized clinical trial. Journal of Veterinary Internal Medicine 30,(6), 1765-1779. Full Article.
Häggström, J., Boswood, A., O’grady, M., Jöns, O., Smith, S., Swift, S., … & DiFruscia, R. (2008). Effect of pimobendan or benazepril hydrochloride on survival times in dogs with congestive heart failure caused by naturally occurring myxomatous mitral valve disease: the QUEST study. Journal of Veterinary Internal Medicine, 22(5), 1124-1135. Full Article.
Keene, B. W., Atkins, C. E., Bonagura, J. D., Fox, P. R., Häggström, J., Fuentes, V. L., … & Uechi, M. (2019). ACVIM consensus guidelines for the diagnosis and treatment of myxomatous mitral valve disease in dogs. Journal of veterinary internal medicine, 33(3), 1127-1140. Full Article.
| Observed Adverse Events | Pimobendan (124) | Benazepril (128) |
| Gastrointestinal disorders (eg, vomiting, diarrhea, anorexia) | 6 | 4 |
| Abnormal behavior (eg, lethargy,confusion, uneasiness) | 3 | 4 |
| Tachycardia (supra or ventricular or both) | 1 | 1 |
| Seizure | 3 | — |
| Polyuria, polydipsia, incontinence | 1 | 2 |
| Dyspnea (intermittent) | 1 | 2 |
| Hepatic enzyme elevation | 2 | — |
| Syncope | 1 | 1 |
| Keratoconjunctivitis | — | 1 |
| Otitis externa | — | 1 |
| Purulent local dermatitis | — | 1 |
| Total | 18 | 17 |
| Pimobendan N = 179 | Placebo N = 180 | |
| Number of dogs experiencing at least 1 severe or worse adverse event | 19 (10.6%) | 19 (10.6%) |
| Number of dogs experiencing at least 1 mild or moderate adverse event (but not a severe or worse event) | 61 (34.1%) | 67 (37.2%) |
| Number of dogs experiencing no adverse events | 99 (55.3%) | 94 (52.2%) |
| Number of recorded adverse events | ||
| Severe or worse | 23 | 21 |
| Mild or moderate | 145 | 153 |
| Total | 168 | 174 |
| Frequency of specifically recorded adverse events | ||
| Diarrhea | 21 | 14 |
| Vomiting | 27 | 27 |
| Anorexia | 7 | 12 |
| Lethargy | 13 | 15 |
| Tachycardia | 4 | 3 |
| Other | 124 | 147 |
| Total | 196 | 218 |
