Pimobendan Transdermal Gel for Veterinary Use

Therapeutic Class: Benzimidazole derivative cardiac inodilator

Species: Dogs

May Be Prescribed For: Congestive Heart Failure (CHF), Dilated Cardiomyopathy (DCM), Mitral Regurgitation

Pimobendan transdermal gel 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 afterload. 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 using 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 about 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 using pimobendan in its 2009 consensus statement about treating CHF due to chronic valvular heart disease.

Most animals with clinical CHF will show a rapid response to pimobendan (one week). Cardiac enlargement generally is 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 nine months. These studies are being repeated in other breeds.

Side effects that were found as a part of the field study for FDA approval for Vetmedin® include loss of appetite, lethargy, diarrhea, dyspnea, azotemia, and ataxia.

Calcium channel blockers and certain beta blockers can decrease the effects of pimobendan.

Pimobendan should not be used to treat 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 also has been associated with an increased incidence in arrhythmias. It is not completely understood at this time if using 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 six-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.

No specific information about 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.

Transdermal gels are one of the easiest but least-known pet-medication delivery methods. These gels allow medications to be absorbed through the animal's skin, so there's no need to force them to swallow pills. Pharmaceutically compounded transdermal gels make medication much easier on pet patients and their owners, and many of the most-common feline medications, including methimazole, prednisolone, and amitriptyline, are available in the transdermal format.