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Dear Daisy Dog

I forgot to give our dog Lola her heartworm pill last month. I called her veterinarian who said to give it this month and every month thereafter, and to schedule a heartworm test in six months.

Years ago, I remember being told that giving heartworm preventive to a dog that actually had heartworms could be fatal. I feel safer getting a second opinion before I give her the pill.

Daisy Responds

Both you and your veterinarian are correct.

You are remembering a drug called diethylcarbamazine (DEC), once sold as Filaribits, a tablet given daily. DEC, which is no longer available as a veterinary product in the U.S., caused potentially fatal anaphylactic shock in up to five percent of dogs that already had heartworms.

Veterinarians now prescribe safer and more effective heartworm preventives, such as Interceptor and Heartgard Plus, chewable tablets given once a month.

Fortunately, these newer medications do not trigger shock in dogs with heartworms.

Now, let me explain why your veterinarian recommended that you have Lola’s heartworm status checked in six months rather than now.

When a mosquito bites a dog and, in the process, injects microscopic heartworm larvae into the dog’s blood, the larvae take five or six months to mature into adult heartworms. Only then will they register on the blood test.

Keep Lola on her heartworm medication throughout the year, because it protects her from not only heartworms but also intestinal parasites, some of which can infect humans.


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