Dear Dr. Mark –
I run an animal shelter and recently picked up an older dog that tested positive for heartworms. Our vet suggested the slow kill heartworm treatment with Advantage Multi because of her age. Everything I’ve read says to give doxycycline for 30 days first with this method, but he is just prescribing the Advantage Multi alone. I’m just trying to get a second opinion as to whether that is advisable and would gladly pay for it. She is not coughing or showing any visible symptoms at all. In case it matters, she had surgery 3 weeks ago to repair a broken femur and goes back tomorrow for her first checkup post surgery. He said not to start the Advantage Multi until after he sees her tomorrow. Any advice you can give would be greatly appreciated!
Michele W.
Hi Michele:
Thank you for your diligent work at the animal shelter and for giving exemplary care to our senior canine companions. We appreciate your dedication.
It sounds like the dog is a good candidate for the slow-kill method of heartworm treatment, as she does not yet exhibit signs such as coughing. You are correct in that the doxycycline is recommended, as research has shown that there are better kill rates (for the heartworms) when used. There are some side effects in some dogs. For instance, gastrointestinal upset (upset stomach), but they are nowhere near as severe as the broken femur or the heartworm. I would start at 10 mg per kilogram twice daily, but if she has trouble with that dose, try to split it up.
Your vet may want to start her as soon as he sees her, since they usually start treatment at the same time as the Advantage Multi®. If not, ask for a prescription and give it to her from day one through day 30.
Why Doxycycline Works to Kill Heartworms
Doxycycline and minocycline, both tetracycline antibiotics, are effective in reducing the bacterium Wolbachia, which is found in and necessary for all heartworm life stages. Essentially, eliminating the Wolbachia bacteria makes the dog’s system inhospitable to heartworms. When vets combine it with Advantage Multi®/Advocate® for Dogs (10% imidacloprid + 2.5% moxidectin), this treatment protocol has successfully converted antigen-positive dogs (heartworm-positive) to antigen-negative (heartworm-negative).
The Savadelis et. al. study that I linked to below demonstrated that this treatment regimen successfully eliminated D. immitis microfilariae (heartworms) by 21 days post-treatment (30 days of doxycycline combined with 10 months of Advantage Multi®). It also reduced heartworm antigen concentration over time and had a 95.9% efficacy in the elimination of mature adult heartworms. [1]
Based on this study, they concluded that this treatment regimen is actually a relatively quick, reliable, and safe option to treat canine heartworm infection. This is compared to other treatment regimens involving macrocyclic lactones. Particularly so, when the medical community’s preferred treatment method, use of the drug melarsomine dihydrochloride, is unavailable, contraindicated, or declined by an owner unable to afford the more costly treatment or concerned about the potential side effects. [1]
Melarsomine as the Treatment of Preference for Heartworm Elimination
Many sources, including the Heartworm Society of America, list the 3-dose protocol of 2.5 mg/kg melarsomine dihydrochloride as the treatment of preference for heartworm elimination in dogs. However, this protocol requires 3 injections, following treatment with doxycycline. The melarsomine protocol can cost between $500-$1500, while some pet insurance companies estimate that costs can rise to $6000 for the successful elimination of heartworms. In contrast, the Advantage Multi®/doxycycline method should range from $350-$450 for preventatives, medications and antigen testing.
Final Thoughts
Considering the insidious nature of heartworms, it is recommended that dogs stay on heartworm preventative year round. If we are keeping the dog on a year round preventative (either Advantage Multi® or Advocate®) the additional cost of the doxycycline and vet visits means the cost of the heartworm treatment alone is $175-$230. Considering the slow-kill method is highly effective and just a few months longer than the preferred protocol, use of the drug melarsomine dihydrochloride, I would highly recommend the slow-kill method for most dog owners.
I hope this information is helpful to you and your vet. Let me know how it is going, and if I can help you at all.
Dr. Mark
Sources
- Savadelis MD, Ohmes CM, Hostetler JA, Settje TL, Zolynas R, Dzimianski MT. Assessment of parasitological findings in heartworm-infected beagles treated with Advantage Multi® for dogs (10% imidacloprid + 2.5% moxidectin) and doxycycline. Parasit Vectors. 2017;10:245. doi: 10.1186/s13071-017-2190-9. [DOI] [PMC free article] [PubMed]
- Summary of the Current Canine Guidelines for the Prevention, Diagnosis, and Management of Heartworm(Dirofilaria immitis) Infection in Dogs1 Prepared for and approved by the Executive Board of the American Heartworm Society, 2014 American Heartworm Society
About the Author
Dr. Mark dos Anjos, DVM, is a seasoned mixed animal practitioner with over 40 years of experience working across Africa, Europe, the US, and South America. He earned his Doctor of Veterinary Medicine (DVM) from the University of Missouri College of Veterinary Medicine. His interests include dermatology, dog training, canine and feline behavior, and exotic animal medicine. Dr. Mark lives on a small ranch in Brazil, where he cares for his horses, sheep, poultry, parrots, and a rescue Capuchin monkey named Niki.
Since moving to a rural region in Brazil, Dr. Mark has been able to work with a variety of wildlife, which he finds immensely rewarding. Notably, his experience with Niki, the Capuchin monkey he rescued, has been one of his most challenging and fulfilling endeavors as a vet.
