🦟 Preventing Heartworm Infection in Dogs – 2025 Vet Guide

Heartworm disease is a life-threatening condition spread by mosquito bites 🦟. Fortunately, modern veterinary medicine offers highly effective ways to prevent it. In this 2025 vet guide, I, Dr Duncan Houston BVSc, will walk you through the safest and best methods of keeping your dog protected—whether through monthly chewables, topicals, or long-acting injections 💉🐶.

💊 How Heartworm Preventives Work

Heartworm preventives kill L3 and L4 larval stages of heartworm acquired in the previous month. Some products also kill older larvae (L5), offering extra protection in case of missed doses. All products are meant to be used in heartworm-negative dogs and should be started after a vet-confirmed negative test ✅.

🧪 Product Categories by Active Ingredient

• Ivermectin-based: Heartgard®, Tri-Heart Plus®, Iverhart Plus®
• Milbemycin-based: Interceptor®, Sentinel®, Trifexis®
• Selamectin-based: Revolution®
• Moxidectin-based: Advantage Multi®, Proheart6®, Proheart12®, Coraxis®

🐾 Ivermectin-Based Products

Ivermectin is safe at heartworm prevention doses even for collie-type breeds. These are generally combined with pyrantel to also protect against roundworms and hookworms:

• Heartgard Plus®
• Tri-Heart Plus®
• Iverhart Max® (adds praziquantel for tapeworms)

Pros: Affordable, safe for most dogs
Cons: No whipworm coverage

🦴 Milbemycin-Based Products

Milbemycin oxime protects against more intestinal parasites (including whipworms) and can also treat demodectic mange at higher doses.

• Sentinel® – adds flea sterilizer lufenuron
• Sentinel Spectrum® – adds praziquantel (tapeworms)
• Trifexis® – adds spinosad (flea killer)
• Interceptor Plus® – adds praziquantel

Pros: Broad spectrum including whipworms
Cons: Greater risk of reaction if used in heartworm-positive dogs

🐶 Selamectin-Based Products (Revolution®)

Revolution® is a topical preventive that protects against heartworms, fleas, mites, and some intestinal worms. It’s especially helpful for pets that hate pills.

Pros: Covers external & internal parasites
Cons: Less effective microfilariae clearance

💉 Moxidectin-Based Products

Offers both monthly and long-acting options. Great for owners who struggle to remember monthly dosing:

• Advantage Multi®: monthly topical with flea killer
• Proheart6® & Proheart12®: injections lasting 6 or 12 months
• Coraxis®: monthly topical, no flea component

Pros: Reliable and hands-free options
Cons: Proheart not for heartworm-positive dogs

🧪 What If I Miss a Dose?

Ivermectin products offer a strong “reach-back” effect: restarting after up to 4 missed months still provides 95% protection. Milbemycin does not perform as well in missed-dose scenarios (41% protection). Regardless, never stop without consulting your vet!

💥 Breed Sensitivities & Safety

• Ivermectin is safe in all breeds at preventive doses
• Milbemycin and Moxidectin are not associated with MDR1 issues
• Large animal ivermectin is NOT safe or legal for dogs

📅 When to Start Heartworm Prevention

If your area accumulates 234 “heartworm development units” in 30 days (temps above 57°F daily), start prevention. In most regions, year-round dosing is recommended.

🧬 Heartworm Resistance Risks

Some resistant strains have emerged in the Mississippi Delta. Be sure to give every dose on time and never use slow-kill protocols for active infections.

🦟 Double Defense Protocol: Repelling Mosquitoes

Use a permethrin-based flea/tick product in addition to heartworm prevention for added mosquito protection:

• K9 Advantix II
• Vectra 3D
• Seresto Collar

📝 Summary Table

🔍 Still Unsure Which Is Best?

Try the free AskAVet.com app and speak directly to a licensed vet who can help choose the best heartworm strategy based on your dog’s breed, location, and health conditions 📱🩺

Protect your dog’s heart year-round—because heartworm prevention is easier, cheaper, and safer than treatment. 💗

— Dr Duncan Houston BVSc