Heartworms are a blood borne parasite. They are exactly as they are named, worms that live in the heart. Heartworms are transmitted by mosquitoes in their larval form and grow to become adult worms that live in the right side of the heart and in the pulmonary artery which supplies the lungs with blood from the heart.
In treating your dog, we will be giving a drug called Immiticide that will kill off the adult worms. This will be done in 2 phases. The first phase will involve a single injection which will kill approximately half of the worms. The second phase will take place a month later and will involve 2 injections, a day apart. This will kill the remaining worms.
The worms that are now in your animal’s heart are slowly doing damage to the heart and main artery which supplies the lungs. This damage can be reversed if we kill the worms in time. If we do not kill the worms, they will eventually and irreversibly damage the heart, lungs, and other organs such as the liver. With enough worms, this condition is fatal.
There is a risk that the immune system will not be able to deal with these worms as they die off and a complication known as thromboembolic disease can develop. For this reason we are prescribing prednisone to be given every other day for the next 2 months. Prednisone has been shown in studies to significantly decrease the risk of the complication. Statistically there is a greater than 95% chance that your dog will be fine. There is less than a 5% chance of a serious complication but some of these complications can be fatal.
After each treatment it is important that you strictly limit all exercise and excitement for one month. That means a total of two months of restriction. Anything that will increase your dog’s heart rate will increase the risk of a complication. As the worms are killed over the next two months, your dog’s immune system must deal with dead worms in the lungs and circulatory system.
The most common sign of a problem will be respiratory difficulty. If your animal appears to be uncomfortable with each breath, or is wheezing or coughing, you should bring them in for us to examine. You can expect that the first day to two days after your pet receives the treatment they will experience some moderate to significant pain. They might pant, or pace uncomfortably. It is not uncommon for them to lose their appetite. They will likely be sore at the site of the injection. These symptoms generally pass after 48 hours at which time your pet should be comfortable and eating normally again.
The Immiticide injections alone generally cost $200 – $400 depending on the size of the dog. The drugs to treat the disease are being provided to you for $50 which you have paid to the Humane Society. The remaining cost of the injections are paid for by Spicewood Springs Animal Hospital and the Humane Society as a service to shelter pets. Your costs will be purchasing heartworm preventative ($25 – $54) and prednisone ($12 – $15), and pain medication ($15 – $20).
We will prescribe tramadol, a pain medication, to help minimize the discomfort associated with the first 24 – 48 hours following the Immiticide injections.

The American Heartworm Society recommends all pets be put on a month long course of doxycycline prior to receiving their first Immiticide injection. This antibiotic kills the bacteria that help the worms thrive therefore weakening them and reducing the workload on the body during the treatment phase. Depending on the dose required, this can run between $20 to $100.

We recommend blood work prior to the first Immiticide injection to be sure that your dog’s liver and kidneys can tolerate the drugs.  In addition we recommend chest x-rays to screen the lungs for damage and to establish a base line x-ray in case of a future complication.  Since these costs are additional and not covered by the Humane Society, you have the option to accept or decline these additional tests and treatments.  Please discuss any questions you have with our staff during your visit.