Pain after Heartworm Treatment

A reader writes in today:

Had our cocker spaniel treated 5 hours ago with his first shot.
For the past 5 hours, he can not get comfortable, fidgets, lays in unusual positions.

When walking, his right rear leg is toeing-in and his walks clumsily, often positioning that right foot too far under his body.
In just the last hour, he has started some toe-dragging with that right foot. Not severe, and he corrects upon moving further into the stepping process.

Also, he has started to drool excessively. Both ears are wet as if he drank from a flat bowl.

Have given him 2.5 mg Diazepam to try to make him more comfortable.

Forgot to mention … the vet had to stick him twice unsuccessfully and then changed needles and successfully administered on the third try.
Do you think he is just experiencing more pain than usual because of the three 'sticks' at the site, or should we be concerned that something else is going on?

 My Reply:

Please call your veterinarian and let him/her know what is happening.

The medicine in the treatment (Immiticide) can cause a lot of inflammation at the injection site. This can occur no matter how smoothly things go and how little it seems to bother the dog at the time.

This can range from being absolutely undetectable to a dog that is crying constantly with pain. Diazepam helps with anxiety, but has no pain relieving properties to speak of.

Please contact your veterinarian about this, as human 0ver-the-counter products can be harmful to your dog. However, it sounds very much like your dog needs pain medication.

The pain usually subsides in a couple of days, and most dogs don't have this type of reaction, but the ones that do get painful do need some help.

The difficulty in walking may indicate that the inflammation is causing enough swelling to put some pressure on a nerve root.  This can be very temporary, but certainly needs to be addressed.

Call your veterinarian and report this situation.  He/she will decide what anti-inflammatory or pain-controlling measures are needed to help your dog.  He/she can't help if they don't know about it.

51 thoughts on “Pain after Heartworm Treatment

  1. Heather says:

    I am total agreement. When my dog Chester was successfully treated with Immiticide last year, he was given a full course of prednisone for joint inflammation and pain. It did wonders. Unfortunately, the drug that’s used (Immiticide) is a form of poison and pain management is important here. Your vet should be made aware of what you are observing so that his pain levels can be addressed.It’s a tough row to hoe, but when it is all done, it’s wonderful!

  2. Doc says:

    Hello, Elizabeth and Crew,

    I also am amazed. Most of my replies advise these folks to let their veterinarian know what is happening. When we don’t hear from the client, we think everything must be okay.

    We try to call our clients back in a day or two to see how things are going. It blows my mind when they are having much worse problems, but didn’t call us to let us know.

    • Rose says:

      My dog had heartworm injections 2 injections, it has been about 3 weeks ago, sometimes when he is laying down he will let out a pitiful yelp. Could something from the injections be still causing him pain? The vet I took him too never gave him any form of pain medicine or didn’t tell us anything what to expect or to bring him back nothing. He has been my dogs cats vet for years but I am getting tired of the way he has been doing. If anyone has any advice about my dog yelping sometimes please leave me a reply. I’m worried????????

      • Doc says:

        Hello, Rose,
        Sorry I got behind this week. I would be surprised if he is still having pain from the injections. The injections are given in the heavy muscle of the lower back. If this is the source of the pain, you would probably be able to feel some swelling, and he would be tender when you put pressure on it.
        I would be concerned about another source of pain. In either case, it sounds like your dog needs a recheck examination.

  3. Pet Supplies Online says:

    According to my opinion heartworm disease is completely preventable. A number of different products with excellent safety profiles are available. Tragically, some studies indicate that a minority of dogs and cats receive the preventatives as they should. Animals in the majority now are at even greater risk.

    • Tracy Corvello Wolfington says:

      I am 60 years old and have owned many a dog and religiously give flea tick and heart worm plus flexadin for joints on my Shepard etc. I have a little dog that got heartworms in sotenof all my care. The manufacturer is paying for the treatment. Sometimes it just happens people and judgements kill me. Oh I looked here because sometimes people just need reassurance.

      • Doc says:

        Hello, Tracy,
        I can appreciate your frustration. Sometimes the medication is not 100% effective. If you were giving the preventive medication regularly, then it is unlikely that there are very many worms present. The outlook for success with treatment is very good, with low likelihood of complications.

      • Jan Moody says:

        Sometimes people are quick to judge I got 2 little dogs they are sisters Chihuahua/Maltese they will be 3 yrs old in June when I got them in Nov 2020 they had never been to the vet I took them well I found out one does have heartworms she weighs 9 pds in the morning she gets her 1st injection I’m worried sick Some one made a rude comment that I should be shot for not giving them preventive meds I didn’t have them then so I couldn’t have given it to them They are my babies now I’m doing all I can for them Rude people should keep thier rude mouths shut

        • Doc says:

          Hello, Jan,
          My father once said to me, “Courtesy costs nothing.” Rudeness is never helpful. We all need to be cautious about criticizing when we don’t know all the facts.

          I understand your worry, but other than some temporary pain at the injection site, we rarely see ill effects from the medication itself. We are more concerned with what happens when the worms die a few days later and shift position in the blood vessels.

    • Sallie says:

      You are correct, however, you may not know the back story and probably shouldn’t be judgy. My beautiful 19 month old American Foxhound started his heartworm treatment today. He’s in a LOT of pain, and is on prednisone, tramadol, and trazodone. He has a miserable 3 months ahead of him. Could this have been prevented? Absolutely, and had he been my dog from puppyhood, he would not have had them. I adopted him two months ago from an animal rescue group. He came from a high kill shelter in North Carolina, where after being diagnosed with heartworms he was scheduled for euthanasia. Lucky for him, and me, they got him out, and had him for about a week before I adopted him, knowing he had heartworms. When I got him on September 8th, he was very thin, his fur was coarse, he was matted with feces, and had infected elbow, and under his mostly white fur, his skin was bright red. Within 10 days of having him, he had been seen by our vet and started on the first part of his heartworm treatment, doxycycline. He, in just two months, has become a full part of our home and he and I truly love each other (and my husband too). He is a healthy, beautiful, and loving dog, with heartworms, which will soon be gone. But I was not careless, just because my lovely Bellino has heartworms, doesn’t mean I am a bad dog parent.

  4. sally webster says:

    I am glad I found this page. My lab just had her first treatment today and she is very restless and only lays down for a few minutes at a time, she is very careful getting up to stand and very slow to lay back down. She has not eat anything since I picked her up from the vet. They did give her tramadol to give 2 pills every 8 hours for pain and 2 benadryl, It seems to help a little but not much. I have cried all evening thinking I have done the wrong thing by having this heartworm treatment done. I had a little dog that had heartworm treatment done 7 years ago and he died,I was very scared to do this with my lab. But the vet said she had to have it done and she is 3 years old and should do well, my Fred was 9 and a half years old and a cocker mix. I still feel the guilt of choosing HW treatment for him and I miss him still. I have prayed for Annabelle to be ok through this.

    • Aimee says:

      I understand your concerns, if you’ve ever seen a dog die from heartworms, it would completely change your mind. I found a lost beautiful healthy well trained pit. We did everything to find his owner to no avail. He quickly stole my heart! We took him to the vet to get him checked out. Everything came back normal (so they said) .. I had him for 3 years (regular check ups, shots, test) .
      In the blink of an eye he went from healthy, hyper, happy, to deathly sick the vet sad he had parvo, that there was a slight possibility he could make it, if we did certain things. But he got weaker and weaker every minute. I stayed up with him just holding and loving him, the next morning he couldn’t use his legs he tried to eat and drink but he threw up everything, I rushed him to a vet ER. To find out he was dying of heartworms, and we had to put him down. Needless to say that vet is no longer working (at least in this town).
      We just found out our 6 year old baby Koda tested positive for HWs right before Christmas and she is starting the treatment next week, without hesitation.

        • Doc says:

          Hello, Lisa,
          Most of my patients are taking monthly heartworm preventive medicines. I have a few that are taking the Proheart 12 injection. This is an economical alternative, and I feel it is effective. Unlike the monthly preventives, it is strictly a heartworm preventive, doing nothing to control intestinal parasites or fleas, as several monthly products do.

  5. Doc says:

    Hello, Sally,

    I suspect by this time that your dog is feeling better. The soreness rarely lasts more than 24 to 48 hours.

    You might ask your veterinarian about increasing dose or frequency. We usually give one 50mg Tramadol tablet per 20 pounds of body weight, up to four times daily, if needed. Dogs absorb Tramadol poorly, so require much larger doses than people of similar size.

  6. Valerie Victoria says:

    I am rescuing a whiten terrier from a no kill shelter he tested positive for heartworms anf has had his first treatments unfortunately he is not doing so well with his mobility with his back legs the vet tech seems to think it could be a underlying condition such as a tumor, because usually dogs will regain strength within a couple of days of treatments he has not. He is eating and drinking has anyone had an experience where there pet took longer to gain strength

  7. Doc says:

    Hello, Valerie,

    Even with dogs that have had very severe pain, all of my patients have gotten back to normal within 2 or 3 days. If your dog is having problems for longer than that, he should be evaluated by your veterinarian.

  8. Deborah Wright says:

    I have a small Terrier that I took possession of
    Taking her to get neutered and shots, found she tested positive for heart worms
    Her first shot, in 24 hours she was much better off
    Now she faces the second shot
    She is a little over a year old
    Can I do compresses or ??? To help ease the muscle pain ???

  9. Doc says:

    Hello, Deborah,

    Cool compresses may help. You should ask your veterinarian about pain medications to help. We do this routinely with our heartworm treatment patients. Some don’t seem to need it at all, but others can be quite painful.

  10. Kathleen Mendel says:

    My little rescue from San Antonio Texas tested positive for heart worm even though he was negative when we adopted him. He is just finished his first injection today and is very restless; repositioning himself every couple minutes. Given him tramadol but apparently not helping. I am a nurse, the way he is acting looks like patients that are going through withdrawals from chemical addiction. I wish I could ease his discomfort. Fearing tomorrow as he will be getting second injection:(

  11. Meghan says:

    My rescue just had the two injection slow kill done. I’ve had him home for an hour and he seems pretty calm laying outside but after ten minutes he wants back inside. However, inside he keeps getting up and repositioning every few minutes and crying. The vet said to start all his meds tomorrow morning. What can I do to help with his discomfort? I would try ice or a warm towel but there is no bald spot so I’m not sure where the injection was done.


  12. Doc says:

    Hello, Meghan,
    Sorry I didn’t get to this earlier. I hope your dog is feeling better now.

    The injections are usually given in the heavy muscle of the lower back.

    A cold pack (not actual ice) would probably have been good. I usually send home Tramadol. Since we give them a cortisone type drug, we can’t use things like Rimadyl (NSAID – non-steroidal anti-inflammatory drug), as they don’t play well together.

    Sorry I got behind.

    • Doc says:

      Hello, Jacqueline, I am sorry to be so late in replying, but our website was re-vamped and the blog comments went into limbo. It is not uncommon for dogs to have some pain after injection. It is usually minor and usually subsides within 48 hours. I usually send home Tramadol with my patients. Many of them don’t need it, but I like for them to have it in case they do.

  13. Brian Garson says:

    I have been feeding my dog Heartgard medicines that I buy from Petcarerx every month. But now I read that some vets are saying that if my dog has a good immune system, preventive medicines are unnecessary and might even be harmful. Is that true by any chance? Or just a marketing strategy for holistic medicines?

    • Doc says:

      Hello, Brian and Brenda,

      Interesting that you two have the exact same comment, word for word. I would be interested to see where you read that “some veterinarians are saying that if my dog has a good immune system, preventive medicines are unnecessary and might even be harmful”. I practice in an area where dogs outside even part time are infected with heartworms after their first mosquito season. Untreated outdoor dogs have their lifespans cut in half. It is a rare dog whose immune system would protect him in this situation. While an individual could be allergic to anything (some people can’t take an aspirin), our heartworm preventive drugs are very safe.

  14. Debra Hellard says:

    My two lab mixes both tested positive for heartworm back in August. They received their 2nd and 3rd injection yesterday and today. The vet tech called and said Max my 3 year old lab pit mix had a little diarrhea. When I picked him up from the vet he seemed ok. We let him go potty before I took him home and while his stool was was more solid there was blood in the stool. I asked the receptionist to let the vet know and to call me in the morning. When we got home he went straight to his pillow to lie down he wouldn’t eat his food and would not touch his meds. They gave him 50 mg of Metradinazole (?)for the diarrhea and his prednisone along with omeaprazole Normally I put his meds in turkey dogs and he has no issues taking them. Well tonight he was super cautious and sensed the hidden meds and wouldn’t touch the turkey dogs…tried cheese and same thing. I’m worried if he doesn’t take his meds he won’t heal 🙁

    • Doc says:

      Hello, Debra,
      I suspect that you have already spoken with your doctor today. If your dog is still unhappy, it could be injection site pain. If that is the case, it usually subsides within 48 hours. I regularly prescribe tramadol for this, sometimes acetaminophen, sometimes acetaminophen plus codeine.

      Diarrhea is not typical, and neither is blood in the stool, so keep your veterinarian informed.

      As far as healing through this process, keeping him from exercising vigorously is probably the most important thing.

      Go with your doctor’s recommendations.

  15. Don says:

    I came to this site with some apprehension, as we are to take our dog, Ruthie, to the vet day after tomorrow for two heartworm shots, a day apart. I’m really concerned both that she has to undergo this, and that she had the same treatment only about 5 months ago, which was–according to her recent blood test–not succeed in killing all the heartworms. I am sincerely hoping that this time it will work. As she is a rescue and has already had to endure who knows what, I hate that we are subjecting her to this, but obviously it is necessary. Much of what I am reading here is helpful. At least it sounds like, although painful, the treatment is rarely fatal. Hoping for the best!! Thanks for the info on this site.

    • Doc says:

      Hello, Don,
      The amount of pain with the treatment is really variable, from none to significant, but generally doesn’t last more than a day or two. We always send home Tramadol to help with the pain (if needed).

      Since you completed a treatment 5 months ago, it is likely that there will be very few worms present now, so little chance of complications. When we perform the treatment, it doesn’t kill developing immature worms. At this point, if you have been giving heartworm preventive regularly, we should be able to eliminate the rest of the worms and just stay on preventive.

      There are a small number of dogs where we cannot eliminate 100% of the heartworms. However, these dogs usually do just fine when we keep them on heartworm preventive year-round.

      It sounds to me like your prognosis is good.

  16. Dylan says:

    I have a couple questions regarding my dogs heartworm treatment. She had her first shot today and was experiencing a tremendous amount of pain, crying no stop and pacing back and forth for hours. What is the best pain medication for dogs that I can request from my vet and can CBD chews be used? I’ve read a lot about people experiencing success with giving their dogs CBD for pain and inflammation. Thanks!

    • Doc says:

      Hello, Dylan,

      We usually send home tramadol with our heartworm patients. I have also used tylenol, and even tylenol with codeine (tylenol #3). I have no experience with the CBD chews. What I read in the literature is that there are a lot of ongoing studies, but no good published data at this time. We also have concerns about the quality of the products available. We see CBD products advertised for sale in pharmacies and gas stations. There is no regulatory oversight on this stuff, so it’s hard to know if the product even has CBD oil in it, much less the quality or amount.

      Usually the pain subsides within 24 hours, even when severe.

  17. Janet says:


    My little rescue Maltese was in a lot pain during first injection of Heartworm treatment (cried and cried in the exam room, there were signs she dedicated), was in a pain after.
    Is there some analgetics or sedatives can be given prior or during next time she will have the shot (second and third injection)?
    Thank you for all comments.

    • Doc says:

      Hello, Janet,

      I rarely have a dog that exhibits more pain with the injection than with any other. However, there are certainly dogs that are very frightened and who just cannot hold still. This can certainly cause problems. I would ask your veterinarian about using some sedation and pain medicine ahead of time. Different combinations work better for different dogs. We sometimes combine gabapentin and acepromazine. Others have used trazodone. There are options out there. I am sure your veterinarian is as anxious as you are to avoid a repeat.

      I repeat that most dogs don’t react to the injection very much. They may develop soreness later, but at the time it’s more the “idea” of getting an injection. The medicine itself is not very painful. But who likes “getting a shot”?

      • carrie says:

        Hello, the melarsomine injection itself IS painful. Melarsomine has a hefty dose of arsenic, basically a chemotherapeutic agent. Within 10 minutes after injection… this hits hard and the worst part is over in about 2 hours. Watched my dog experience this recently. Basically we are trying to poison the worms without killing the dog. It is intense.
        After the first few hours of sheer pain, seems like dogs whine the rest of the day due to feeling completely out of sorts.

        • Doc says:

          Hello, Carrie,
          I am sorry that your dog was one of the patients who had more pain. I have personally treated thousands of dogs and the reactions run the gamut from no apparent pain to excruciating pain that lasts for 2 days. One patient had a very bad reaction, actually sloughing some tissue. Many patients seem just fine, and the owners don’t give the pain meds we send home. Some need additional pain meds.

          I have never been able to predict which dog will have trouble. It doesn’t seem to matter whether young or old, fat or thin, heavily muscled or not, active or lazy. There is just no rhyme or reason to it.

          The majority of dogs have minor pain for about a day.

  18. Holly says:

    Hi. My rescue came with heart worms and has completed the 3 injections. He seemed fine after the first 2 however became very sore at injection site following the 3rd. After the steroids and pain killers kicked in he was doing much better. As we began to taper the steroids he was in a lot of pain again, helping if and holding his leg up. He is now on gabapentin (200 mg and he’s only 20lbs) and rimadyl for the pain. It was working for a few days and now he is in extreme pain again. His last treatment was 5 weeks ago. We are headed back to the vet tomorrow but I am afraid that there is permanent nerve damage or something. Have you ever heard of the leg pain lasting this long?

    • Doc says:

      Hello, Holly,

      I have never run into this situation. The injections are given in the muscle of the lower back. It is possible that there may have been some medication that contacted spinal nerves if the dog were to jump during the injection process. I have had dogs jump and have felt the tip of the needle contact the lateral spinous process of the vertebra. I have had one patient who developed such a tissue reaction that there was an open sore.

      However, I have never seen anything like you describe as a consequence of treatment. It makes me wonder if there is not some other disease process going on.

      • s says:

        what happened with the dog that developed the tissue reaction? is this a minor complication if it happens or are there long term consequences?

        • Doc says:

          Hello, Sevoruc,

          With one exception, I have seen only minor complications. There was one dog out of thousands who actually sloughed an area of tissue. This did heal in, but it was a significant problem.

  19. Donna B says:

    I just want to thank all of you for the information provided here. I recently adopted a sweet 3 yr old rottie mix. She is a little love bug. I took her to the vet the day after I got her and was told she was heart worm positive. My heart broke. I took in a stray when I was a teenager. He tested positive and I had him treated. He only lived 3 weeks and 2 days after the treatment. I was hesitant to go through it again. I even considered euthanasia rather than putting her through it only to have her die. However, I decided to give it a try. She got one two days ago; they gave her second shot yesterday and sent her home. Last night wasn’t too bad. She was sensitive along her ack. Today I have cried with her. She can’t seem to move without crying out in pain. I called my vet this morning and they had me pick up prednisone for her. Then I found your blog. I needed reassurance this was normal and that she has a fighting chance. Sorry to be so long winded. And I am outraged she was not given preventive medicine. I think owners should be prosecuted for animal cruelty/neglect when they don’t.

    • Doc says:

      Hello, Donna,

      Sometimes people aren’t intentionally neglectful, just ignorant of what they need to do. There plenty of people who don’t care for themselves or their children, so it’s not surprising they don’t take very good care of their animals.

  20. Terri says:

    I rescued a 3 yr old chihuahua which I found out HW positive, he was very lethargic to the point I honestly thought he was dying , poor appetite and would vomit . After visiting vet I chose to do the fast kill method but we had to start on antibiotics , advantage multi topical for 3 months prior to injections, he wasn’t doing so well. Vet chose to proceed with the injections and I was terrified for him as he was so tiny weighed 4.3 pounds . He tolerated first injection and I chose for him to spend 2 days at the vet hospital only because of his condition, came time for 2nd round which I was informed that could be worse for him, he did great with very little side effects, he tested positive after 6 month follow up despite my being faithful in administering topical HW advantage multi, I was heart broken. He received another 3 months of the topical and I am happy to report he is HW negative and is active happy little guy that has brought more joy and happiness to my life. Please HW are preventable but deadly, keep your pet on year round prevention, if you can’t afford the medication then you can’t afford to be a pet owner,

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