Your pet’s medication and the “therapeutic window”

Some medications have a narrow therapeutic window

Back when I was in school, one of my teachers wanted to explain something called “therapeutic window” to the class. My teacher explained that you could draw a graph and put one line above and call it “toxic dose above” and another line under the first line called “ineffective dose below.” The distance between those two lines is the level that any drug needs to be in to be safe and effective and is called the “therapeutic window.” This distance is different, depending upon the specific medication, essentially making some drugs safer than others in terms of dosing errors such as giving an inadvertent extra dose, or an accidental overdose by the pet.

An example of a medication that has a very narrow therapeutic window is called digoxin. There is no room for error when giving medication that has an effective dose which is near the toxic dose (a narrow therapeutic window.) The best way to avoid a potential major problem is to keep the appointments with your veterinarian so that blood levels can be drawn and assessed regularly as needed.

Digoxin is a drug with a narrow therapeutic window

Digoxin, which is a very common medication in treating heart failure, is not the only medication that requires careful monitoring due to a narrow therapeutic window. This week, in addition to discussing medications with a narrow therapeutic window, I would also like to address heart failure in pets, its causes and its treatments. If properly used, digoxin is actually an extremely beneficial drug in treating heart failure, and it is therefore commonly used by caring pet parents under the guidance and care of a veterinarian.

If a heart disease is left undiagnosed and untreated, it can result in the failure of the heart to pump blood properly and efficiently. When this occurs the body attempts to compensate for this failure and starts organizing the things needing to get done and how they are done. When this compensation stops working in time, there is a decrease in the heart function which can eventually lead to heart failure. One of the primary points in treatment is to decrease the amount of the compensation that the heart undergoes and to prevent the effects of long term failure. These primary treatment goals include eliminating the original causative problem, getting the heart rhythm normalized, getting the electrolytes normalized, and improving survival and quality of life.

Diuretics, sometimes called “water pills,” are usually the first line of treatment for the swelling caused by heart failure. A medication called enalapril, along with similar drugs in its class, can be used to decrease the constriction of blood vessels which can make the heart failure much worse. Another medication that is the “classic” drug for managing heart failure is none other than digoxin which we already mentioned for having a narrow therapeutic window. Digoxin, however, is not too expensive and it works great in many pets. This drug’s claim to fame is the fact that it has the double benefit of not only increasing the force of the contraction but also can have a cardiac slowing down effect.

Vetmedin for the treatment of heart failure

Another recent newcomer on the scene for the treatment of heart failure is called Vetmedin (pimobendan). This medication opens the blood vessels so the resistance against the heart is decreased, improving the efficiency of the pump. Vetmedin is a truly wonderful new addition to the treatment of heart failure and seems to be helping this condition tremendously thereby improving the pet’s quality of life.

The bottom line is that there are many treatment options for this disease and your pet can have a long happy life if treatment begins early. The way to give your pet the best chance of survival is by getting a proper diagnosis by a veterinarian. Once the pet is diagnosed then treatment can begin right away and the numbers of happy years you will have together have potential of increasing tremendously.

Develop a good relationship with your pet’s veterinarian and don’t be afraid to ask questions. Additionally, a 1800PetMeds pharmacist is available to answer any questions that you may have regarding the medication your pet is taking. Call us and chat if you have something that you would like get more clarification on.

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