Heartworm Treatment in Dogs: A 2025 Veterinary Guide to Safe and Effective Protocols 🐶🫀

Hello, I’m Dr Duncan Houston BVSc. Heartworm disease is life-threatening, but with the right treatment plan, dogs can survive and recover. In this 2025 veterinary guide, I’ll walk you through how we evaluate cases, what medications are used, and which approach is safest for each type of patient. 🦟

📋 Evaluating Heartworm Cases

Dogs are classified into one of four stages to guide treatment:

• Class I: No symptoms, mild findings on X-rays
• Class II: Mild symptoms (occasional cough), lab signs of heart damage
• Class III: Severe signs—weight loss, breathing issues, heart damage on X-rays
• Class IV (Caval Syndrome): Life-threatening. Collapse, brown urine, heart failure. Requires surgical removal of worms via the jugular vein 🏥

💉 Three Worm Stages to Treat

1. Microfilariae: Baby worms in the bloodstream. Must be cleared to prevent spread via mosquitoes.
2. Immature Larvae (L3, L4, early L5): Newly arrived via mosquito bite. Can be killed with standard preventives.
3. Adult Worms: Live in heart and arteries. Must be killed with arsenic-based medication (melarsomine).

🛑 Step 1: Stabilize the Patient

• 🏃‍♂️ Strict exercise restriction—before, during, and after treatment
• 💊 Use steroids if inflammation is significant

🔫 Step 2: Kill Microfilariae and Larvae

These stages are targeted with macrocyclic lactone preventives (like ivermectin or moxidectin). Caution: high doses can cause severe reactions if too many microfilariae are present.

• Advantage Multi® (moxidectin): FDA-approved microfilaricide—preferred for safety
• Low-dose ivermectin (Heartgard): Slower but safer in some dogs

🦠 Step 3: Kill Wolbachia Bacteria

Wolbachia bacteria live inside heartworms and fuel inflammation. We use:

• Doxycycline: 28-day course helps sterilize and weaken heartworms

☠️ Step 4: Kill Adult Worms

Melarsomine dihydrochloride (Immiticide® / Diroban®) is the only drug that kills adult worms.

Protocols:

• Three-dose (split-dose): Preferred for safety. 1 injection → 1 month later, 2 more 24 hrs apart
• Two-dose: Less safe, sometimes used for mild infections

Post-Injection Care:

• 💢 Injection site may be painful—expect soreness for 1–4 weeks
• 🛌 Strict rest for 30 days post-treatment
• 📞 Contact your vet if signs like coughing, fever, or nosebleeds occur—especially in the 7–10 days after treatment

🐢 The "Slow Kill" Option (Mox-Dox)

For shelters or mild cases, slow kill can be an alternative. But it has tradeoffs:

Method:

• 💊 Use Advantage Multi® monthly
• 💊 Give doxycycline for 28 days
• 📉 Microfilariae clear in 3–4 weeks
• 🪱 Adult worms die gradually over 3–6 months

Note: The dog still has heartworms during this time. The disease can progress, and exercise restriction is still needed. Use only if melarsomine is unavailable or cost-prohibitive. 💰

📅 Monitoring After Treatment

• 🧪 Retest antigen levels 9 months post-treatment
• 📉 Repeat monthly if positive
• 💊 Consider second treatment or slow-kill reboot if still positive at 15 months

📱 Ask A Vet: Navigate Treatment Safely

Managing heartworm takes coordination. Ask A Vet can help with:

• 🩺 Interpreting test results
• 💊 Mapping out your dog’s treatment timeline
• 🔁 Supporting side effects & post-injection care
• 🧼 Preventing re-infection at home

Download the app or visit AskAVet.com for 24/7 expert support. 🐾

✅ Summary: Heartworm Treatment in 2025

• 🧪 Step 1: Confirm infection and stage the case (Class I–IV)
• 🛑 Step 2: Stabilize & restrict exercise
• 🦟 Step 3: Kill microfilariae, larvae & Wolbachia
• ☠️ Step 4: Use melarsomine for adult worms (3-dose preferred)
• 🐢 Slow kill is a backup—not a substitute
• 📅 Retest in 9 months and again monthly until negative

With proper care, most dogs fully recover and go on to live long, healthy lives. Let’s beat heartworm disease together—safely and confidently. 🐶❤️

— Dr Duncan Houston BVSc