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Pimobendan for Veterinary Use
by Barbara Forney, VMD
Pimobendan is a relatively new and unique inodilator (inotropic, mixed vasodilator). Its positive inotropic actions are caused by both inhibition of phosphodiesterase III and increased sensitization of myocardial contractile proteins to calcium. Digoxin and other inotropic drugs increase cardiac contractility by increasing the amount of intracellular calcium. Pimobendan improves systolic efficiency without the negative pathway of increasing intracellular calcium. Pimobendan increases cardiac output and reduces both the cardiac preload and after load. It is usually used in conjunction with other cardiac drugs (furosemide, digoxin, and enalapril). Pimobendan is metabolized by the liver
Pimobendan is used to treat CHF due to atrioventricular valvular disease or DCM. Large clinical studies support the use of pimobendan in dogs that are symptomatic for CHF and in breeds of dogs that are at risk for the development of CHF due to DCM. The literature is consistently favorable regarding improvement in exercise tolerance, quality of life and heart failure score. In one study of dogs with CHF due to atrioventricular valvular disease; the dogs that were treated with pimobendan survived 415 days in contrast to a survival time of 128 days for those that were treated with conventional cardiac drugs. The American College of Veterinary Internal Medicine has recommended the use of pimobendan in their 2009 consensus statement regarding the treatment of CHF due to chronic valvular heart disease.
Most animals with clinical CHF will show a rapid response to pimobendan (one week). Cardiac enlargement is generally decreased within 30 days of treatment and the degree of size reduction is correlated with improvement in clinical status and increased survival time. The studies of dogs that are at risk to develop CHF due to DCM have been performed primarily with Doberman Pinschers. The results are strikingly positive with an increased life expectancy of 9 months. These studies are being repeated in other breeds.
Side effects that were identified as a part of the field study for FDA approval for Vetmedin
® include loss of appetite, lethargy, diarrhea, dyspnea, azotemia and ataxia.
- Pimobendan should not be used for the treatment of hypertrophic cardiomyopathy, aortic stenosis, or any condition where increased cardiac output is inappropriate.
- Pimobendan has been associated with an increased incidence of arrhythmias (both atrial fibrillation and ventricular ectopic beats) but the progression of CHF has also been associated with an increased incidence in arrhythmias. It is not completely understood at this time if the use of pimobendan in animals with CHF is causing an increased incidence of arrhythmia independent of the underlying heart disease.
- Pimobendan has not been tested in pregnant animals, nursing animals or those less than 6 months old. It has not been evaluated in dogs with concurrent serious metabolic problems such as diabetes. Not evaluated in dogs with congenital heart defects.
Calcium channel blockers and certain beta blockers may decrease the effects of pimobendan.
No specific information regarding overdose was found. As a part of the approval process healthy dogs were administered 3X and 5X normal doses for six months without any mortality
About the Author
Dr. Barbara Forney is a veterinary practitioner in Chester County, Pennsylvania. She has a master's degree in animal science from the University of Delaware and graduated from the University of Pennsylvania School of Veterinary Medicine in 1982.
She began to develop her interest in client education and medical writing in 1997. Recent publications include portions of The Pill Book Guide to Medication for Your Dog and Cat, and most recently Understanding Equine Medications published by the Bloodhorse.
Dr. Forney is an FEI veterinarian and an active member of the AAEP, AVMA, and AMWA.
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Wedgewood Pharmacy's compounded veterinary preparations are not intended for use in food and food-producing animals.