As a rule, most of these drugs are well tolerated by a healthy animal. But as a rule, heartworm disease does not affect a healthy animal. Why risk an adverse reaction. And there is a risk.
In her blog, Dr. Dodds states:
Some individual animals affected with autoimmune diseases and their immediate relatives have been shown to react adversely to commercial, monthly heartworm preventives. When an individual’s immune system is compromised, any regular exposure to particular kinds of drugs, chemicals or toxins can produce significant adverse effects, whereas these exposures are well-tolerated by animals with healthy immune systems that do not carry the genetic susceptibility to these disorders. It is important to emphasize that the licensed drug or chemical is safe unless used in a genetically or physiologically susceptible companion animal. These adverse reactions usually occur within the first 10-14 days after the monthly product has been administered and typically begin after an animal has had 2-5 doses. Occasionally, animals that have been taking monthly preventives for a relatively long time will develop subsequent product intolerance. This usually indicates that some underlying disease process has emerged to explain the problem. Based on cumulative data, it is my recommendation that dogs affected with autoimmune diseases and their immediate relatives receive only plain daily heartworm preventive (Dimmitrol = diethylcarmbazine). If heartworm disease is not prevalent where the animals live, routine use of heartworm preventives is not recommended. This is especially important for dogs suffering from chronic diseases of the skin, hair and coat, or those with bone marrow, thyroid or liver disease.
Please click through to the post to get her recommendations for administering heartworm medicine at a 45 day interval rather than 30 and only in those months when mosquitoes fluorish.
Her last note cautions dog owners about the use of Trifexis and Comfortis - marketed as both a heartworm and flea preventative.
Spinosads are found in Trifexis, a monthly heartworm/flea preventive, as well as Comfortis for flea prevention. While I believe these are effective for flea prevention and killing, spinosads are contraindicated in epileptic or seizure prone dogs and should not be given to these dogs. Unfortunately, this is generally unknown and should be shared with your veterinarian, friends and family.Is there a safer alternative?
My dog was one suffering so much chronic disease and make no mistake - allergies are a direct reflection of a compromised immune system - I chose to forego regular heartworm preventative. For one, it's not a preventative. The drug kills any heartworm microfilia that may be present. For another, heartworm disease is fast-acting. It's not going to kill your dog overnight. I had my dog's blood tested every six months for heartworm disease. Would he have been infected, the prevention was also the cure.