Your Dog Missed A Dose Of Heartworm Medicine…Now What?

Most monthly heartworm medications offer coverage for heartworm prevention beyond the typical 30 days.

A common question clients often ask is what they should do if they missed a dose of heartworm medicine: Should they have their pet tested first before giving another pill?  The answer to this question is no.  Fortunately, most monthly heartworm medications do offer coverage for heartworm prevention beyond the typical 30 days. The product Sentinel,  for example, is  often effective for 45 days, while Heartgard or Iverhart may be effective for up to 2 months; therefore, animal guardians can simply often resume giving the preventative at the appropriate time the next month.

If a pet misses more than one dose and up to 6 months, I will often instruct the client to simply restart the medication as well, in addition to instructing them to have their annual vet exam and heartworm testing at that time. It takes at least 6 months for a pet to become seropositive on blood tests after being bitten by a mosquito carrying heartworm larvae. Therefore, in clients missing more than 6 months of heartworm preventative medication, it is best to have the blood test first before resuming the administration of the medication.

Another common question asked is if a pet vomits after the administration of heartworm medication, I will typically tell clients to resume the monthly heartworm medication the following month. If vomiting occurs with subsequent administration, it may be best to change to a different brand of monthly heartworm medication or consider the topical medication Revolution, due to the possibility of having an allergy to the ingredients in the preventative.

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  1. i think it can be harmful to miss a dose……….

  2. The test of HW was positive for two of my dogs and I need two treatments. One of my dogs weights 58 lbs., and the another is 64 lbs.

    • Dr. Michael Dym, VMD veterinarianApril 17, 2014 at 11:38 pm · Reply

      I would recommend seeing local vet for possible heartworm adulticide treatment with injectable drug called immiticide.

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  4. I have a for year old sweet Beagle/Rat Terrier Mix I adopted and he was HM + when I got him two years ago. These past 3 months have really taken a toll on me financially and was not able to get his Hartguard. Will he be okay? What can I do to ensure he will live for a long time? Thanks.

    • Dr. Michael Dym, VMD veterinarianJune 29, 2014 at 4:25 pm · Reply

      I would just feed him an all natural diet like wysong epigen diet from 1800petmeds, as well as get him heartworm tested and back on heartworm prevention. Consider multi vitamin like vita chews from 1800petmeds, as well as antioxidant like proanthozone for long term health.

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  6. I have a question concerning Heartworm medication,and my dog vomiting. I normally feed my dog twice per day..Today it was time for my dog’s monthly Heartworm medication dose,so I gave my dog her Heartworm medication along with her first feeding at 1:30pm,and then her evening feeding later around 8:00pm.

    At 11:30pm she vomited while I had her outside.What happened when I took her outside was,is that I walked down the stairs of my deck into the yard,and turned around to see where she was at because she wasn’t in the yard with me,and then noticed she was eating something up on the deck.So I quickly went back up the stairs to see what was going on,and then noticed she was eating vomited,swollen nuggets of the dry dog food.I don’t know how much initially was vomited up because she was eating quickly when I got to her.After pulling her away from the vomited food,I counted 19 peices of food nuggets left over.The food nuggets are the small size ones,so there’s quite a few in each 3/4 cup/twice a day serving,so volume-wise dry it isn’t that much..but I don’t know how much she vomited initially before she ate some of it by the time I got to her..or if it makes any difference at all?

    What I’m not sure of here,is whether the dog food and Heartworm medication combination I gave her 10 hours earlier at 1:30pm was already far enough along in the digestive process,so the medication was fully absorbed by 11:30pm,and the food that she vomited was just from the later,second feeding at 8:00pm?…or if I’m going to need to re-dose her again?.


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