- Little Jo Wheek
Cardiac (heart) drugs have many different categories and uses. The most commonly used in guinea pigs seem to be ACE-inhibitors like enalapril (Enacard), captopril (Capoten), lisinopril, or benazepril HCL (Fortekor, Lotensin). These drugs work by inhibiting an ezyme called angiotensin converting enzyme (hence the "ACE") which in turn ends up causing vasodilation. The end result is increased cardiac output (more blood volume pumped through body) and a lower general blood pressure.
Pimobendan (vetmedin) is in a different class of drugs, however, than ACE-inhibitors. It is in a class called calcium channel blockers. Some of these drugs have multiple effects and are in other cardiac drug categories as well. Other calcium channel blockers include amlodipine besylate (Norvasc), diltiazem HCL (Cardizem, Tiamate, Diltiazem, etc.), and verapamil HCL (Calan, Isoptin, etc.). These drugs are primarily antiarrhythmic drugs--that is to say they keep the heart beating regularly. One of the problems with heart disease is that the heart can beat faster (tachycardia) and/or irregularly (arrythmia) which creates many problems. These drugs primarily block calcium from having an effect on the muscles of the heart (the heart is basically composed of mainly muscle). This causes the heart to not contract like it would if it was trying to beat too fast. They can also effect electrical activity on the heart (which can pretty much slow heart rate, too). Another effect of inhibiting calcium can also cause some vasodilation which reduces blood pressure. Amlodipine is well known and used in cats for that specific reason.
One of the problems in treating heart disease is the type of heart problem. There are other cardiac drugs that are indicated for other diseases. Cardiac ultrasound is really the only way to tell which heart problem is causing the murmur (whether it is a certain valve or what). Some problems do well on treatment that is not necessarily the appropriate treatment for the problem due to the alleviation of clinical signs. For example my guinea pig, Antoine, had a murmur that affected his pulmonary valve. The disease was called pulmonic stenosis and the treatment is usually surgical. For multiple reasons, open heart surgery was not available nor indicated in his case. There is no other "cure," but due to his decreased heart output, he did well on ACE-inhibitors which raised the cardiac output.
Most guinea pigs are not completely worked-up and diagnosed as to the specific heart problem (sometimes due to lack of informed radiologists to ultrasound the heart). Thus, treatment is empirical, or based on clinical signs, a good DVM's expertise, and response to treatment.
I hope to post a few links on pimobendan and other drugs as they become available. Not addressed here are potential drug interactions (of which there are many) and doses--especially when used with other drugs. Using several drugs at once can increase the chance of adverse effects (like low blood pressure with cardiac drugs) and generally reduce the dose of each drug needed to achieve therapeutic effects. I have also not gone into diuretic drugs like furosemide (Lasix) which reduce tissue fluid left with poor heart function. That's for another thread ;)
If anyone has any clinical information as well as anectdotal info on these drugs, please post here to share!
- Little Jo Wheek
I also meant to say something about the fact that pimobendan is listed as a Ca channel blocker as well as partially phosphodiesterase inhibiting. I already explained the Ca blocking. The phosphodiesterase is an enzyme that blocks vasodilation, so if you block it you allow vasodilation.
- Scrapbook Addict
I'd rather have all the information I can before I call my vet since she asks me to do the research anyway.
Currently my heart pigs are on once daily Lotensin only, and they seem to be okay, but if there's anything else that will help them I'd like to explore the possibilities.
I have a 6 year old boar with a murmur, who has had 2 increases in his Enacard in the last 6 months and I'm looking for anything that might help him extend the quality of his life.
From my searching here, it sounds like Pinta has been using and has had good results. I guess I would like to hear more about it.
We had stopped using it in Fanny but her heart seemed to get worse as her hyperthryroidism progressed so we put her back on. She's pretty stable now. With her, weight is an indication of stability.
- Little Jo Wheek
www.wedgewoodpharmacy.com for pimobendan compounding