How are dogs treated for heartworms?
There is some risk involved in treating dogs with heartworms, although fatalities are rare. The drug that is used contains arsenic. The amount of arsenic is sufficient to kill heartworms without undue risk to the dog. However, dogs with poor liver or kidney function may have difficulty breaking down and eliminating the arsenic. In spite of this we able to treat more than 95% of dogs with heartworms successfully.
We see some dogs with advanced heartworm disease. This means that the heartworms have been present long enough to cause substantial damage to the heart, lungs, blood vessels, kidneys, and liver. A few of these cases will be so far advanced that it will be safer to just treat the organ damage rather than risk treatment to kill the worms. Dogs in this condition are not likely to live more than a few weeks or months.
Treatment to kill adult worms: An injectable drug to kill adult heartworms is given for two days. It kills the adult heartworms in the heart and adjacent vessels over a period of about 30 days.
Complete rest is essential after treatment: Some adult worms die in a few days and start to decompose; the remainder will die within a month. As they break up, they are carried to the lungs, where they lodge in the small blood vessels and are eventually reabsorbed by the body. This is a dangerous period, and it is absolutely essential that the dog be kept quiet and not be allowed to exercise for 1 month following treatment. The first week after the injections is very critical because the worms are dying. A cough is noticeable for 7 to 8 weeks after treatment in many heavily infected dogs.
Prompt treatment is essential if the dog has a significant reaction in the weeks following the initial treatment, although such reactions are not common. If a dog shows loss of appetite, shortness of breath, severe coughing, coughing up blood, fever, and/or depression, you should notify us. Response to antibiotics, cage rest, and supportive care, such as intravenous fluids, is usually good in these cases.
Treatment to kill microfilaria: Approximately one month following treatment to kill the adults, the dog is returned to the hospital for administration of a drug to kill microfilariae. Your dog needs to stay in the hospital for the day. Seven to ten days later a test is performed to determine if microfilariae are present.
If they have been all killed, the treatment is complete. If there are still some present in the blood, treatment for microfilariae is repeated.
In some cases, the heartworm infection is "occult," meaning that no microfilariae were present. In this case, a follow-up treatment at one month is not needed.
Other treatments: In dogs with severe heartworm disease, it may be necessary to treat them with antibiotics, special diets, diuretics to remove fluid accumulations, and drugs to improve heart function prior to treatment for the heartworms.