Pet parents know the importance of maintaining a monthly regimen of heartworm preventative for their four-legged family members but one popular brand may no longer be working.

Heartworms are nasty parasites. Treatments for infected pets are often lengthy and expensive and left untreated, can be deadly. That's why preventive drugs are so important. Heartworms are transmitted through the bite of an infected mosquito and since we live in an area that has a large mosquito population, especially in the summer months, the risk of heartworms is that much higher. Personally, my cat, Jupiter Jack, doesn't even venture outside, but because mosquitos do sometimes find their way inside the house from time to time, we keep him on preventative as well out of an abundance of caution.

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It can be hard to determine what medications are best for our pets and we rely heavily on the information that we receive from our veterinarians to make informed decisions. One Evansville animal hospital is warning their pet parents after finding that a popular heartworm preventative is no longer effective in preventing the parasite. Evansville's Greenbrier Animal Hospital made a post to social media about concerns regarding Heartgard Plus, saying that not only will they no longer be writing new prescriptions for it but that they will no longer be filling outside prescriptions either. The decision comes after learning that several of their patients have tested positive for heartworms despite being treated with Heartgard Plus. Greenbrier Animal Hospital, located on North Green River Road, says they believe that the parasite has built up a tolerance to the active ingredient in the medication - ivermectin.

In their post, they write,

Over the past year, we have had many dogs that have been on Heartgard Plus monthly show positive on their yearly heartworm test. And we have sent out samples to the lab to confirm this. There is a strain of heartworm that is resistant to ivermectin, the active ingredient in Heartgard Plus.

We've experienced a similar phenomenon of resistance with over-the-counter flea medications in the past. (You can read more insecticide resistance in fleas from the National Center for Biotechnology Information here) Obviously, you will want to consult with your own veterinarian regarding your pet's heartworm medication, but this is certainly a compelling reason to consider changing preventative medications.

[Source: Greenbrier Animal Hospital via Facebook]

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