Lecture 18- Heartworm Infection and Disease in Dogs: Part 3 Options for Treatment

What are the three phases of heartworm treatment?

1Pre-adulticide clinical evaluation and treatment

2. Adulticide treatment

3. Post-adulticide evaluation and treatment

What is involved in the pre-adulticide clinical evaluation and treatment phase?

Clinical evaluation

Removal of heartworm larvae and Wolbachia

What is the purpose of adulticide treatment in heartworm therapy?

To kill adult heartworms that are ≥ 100 days post-infection in the pulmonary artery.

Which drug is used for adulticide treatment in heartworm therapy?

Melarsomine dihydrochloride

How many injection protocols are available for melarsomine dihydrochloride?

Two or three injection protocols are available.

What are "Slow Kill" alternatives in heartworm treatment?

A treatment option that is not endorsed by AHS, CAPC, or FDA labeled.

What is involved in the post-adulticide evaluation and treatment phase?

Antigen testing to verify treatment effectiveness

Microfilaria testing and treatment if necessary

Why is antigen testing performed in the post-adulticide phase?

To verify the effectiveness of the adulticide treatment.

What is the purpose of microfilaria testing after adulticide treatment?

To detect any remaining microfilaria and treat them if necessary.

What are the key components of the pre-adulticide clinical evaluation at diagnosis?

Classify the patient as symptomatic for clinical disease or asymptomatic

Blood chemistry panel (kidney function, liver enzymes)

Radiographic evaluation

Blood examination for microfilariae

What is the goal of the first treatment within the first 30-45 days prior to diagnosis?

To remove migrating heartworm larvae.

What monthly prophylactic treatments are acceptable for removing heartworm larvae?

Ivermectin

Selamectin

Milbemycin

Moxidectin

Note: Choose a drug with low microfilaricidal activity.

What is the purpose of doxycycline treatment in early heartworm therapy?

To remove Wolbachia bacteria

Reduce the risk of thromboembolic complications

Enhance the effectiveness of the adulticide

Make microfilariae uninfective to mosquitoes

How is doxycycline dosed in early heartworm treatment?

10 mg/kg BID for 4 weeks.

What is the second treatment given at Day 30 post-diagnosis?

A second monthly prophylactic treatment.

What is the purpose of adulticidal treatment in heartworm therapy?

To remove adult heartworms in the pulmonary artery and right ventricle.

What drugs are used for adulticidal treatment?

Immiticide (Melarsomine Dihydrochloride) or Diroban.

What are the benefits of Immiticide treatment?

Safe and highly efficacious (90-98% effectiveness)

Only effective against adult worms in the pulmonary artery at ~100 days post-infection

Low risk of hepatotoxicity

Pulmonary thromboembolism risk

What is the FDA-approved Immiticide treatment regimen for stabilized Class 1 and Class 2 cases?

2.5 mg/kg, IM deep epaxial lumbar, SID

Administered 24 hours apart

What is the AHS/CAPC recommended Immiticide treatment regimen?

2.5 mg/kg, IM deep epaxial lumbar, SID, at Day 60

Repeat 2 more times (Day 90 & 91)

What is the recommended post-adulticidal care for treated animals?

Cage rest and leash walks for 6 to 8 weeks.

What is the original "Slow Kill" treatment for heartworm disease?

Ivermectin, shown to be efficacious over extended periods (71% effective over 24 months, 95% over 29 months).

What are the risks associated with the original "Slow Kill" ivermectin treatment?

Pulmonary thromboembolism risk

Ongoing heartworm-associated inflammatory disease

What is the new "Slow Kill" regimen (Bazzocchi et al 2008)?

Ivermectin 6 to 8 μg/kg, SID every 15 days for 6 months

Doxycycline 10 mg/kg SID for 30 days

78% efficacy at 36 weeks post-treatment

Kills microfilariae by 12 weeks

What is the Moxi-Doxy treatment regimen (Savadelis et al 2017)?

Advantage Multi (Imidicloprid + Moxidectin) monthly for 10 months

Doxycycline 10 mg/kg BID for 30 days

95.9% efficacy in eliminating adult heartworms

Kills microfilariae by 21 days

What are the concerns with "Slow Kill" treatments, especially post-adulticidal treatment?

Risk of thromboembolism due to dead, dying worms in vascular circulation

Exercise restriction and corticosteroids are used to manage the inflammatory response

Why is prednisone use questioned in heartworm treatment?

Prednisone may increase the risk of thromboembolism, aggravate intimal disease, act as pro-coagulants, and reduce pulmonary blood flow necessary for clearing deteriorating worms and debris.

How does doxycycline treatment help in heartworm therapy?

Mitigates the inflammatory response

Reduces pathological changes

Renders microfilariae uninfective to mosquitoes

Why is the FDA-approved 2-injection regimen of melarsomine considered cost-effective?

It has demonstrated 96% efficacy since 1995 with a single treatment followed by two treatments 24 hours apart.

When is the "Slow Kill" approach typically rejected?

Due to prolonged therapy, ongoing pathology, and the potential for emerging drug resistance.

What is the advantage of the new "Slow Kill" regimen with doxycycline?

Demonstrated to reduce the adverse effects of Wolbachia and make microfilariae uninfective to mosquitoes.

What is the primary concern when using "Slow Kill" treatments?

All regimens have pros and cons regarding efficacy and safety. Melarsomine is the only FDA-approved adulticidal treatment, but Moxi-Doxy is a promising alternative, though not endorsed by AHS or CAPC.

What is the original "Slow Kill" ivermectin treatment for heartworm disease?

Ivermectin treatment shown to be efficacious over extended periods (71% effective over 24 months, 95% over 29 months).

Pulmonary thromboembolism risk.

Heartworm-associated inflammatory disease still ongoing.

What are the post-adulticidal risks associated with "Slow Kill" treatments?

Pulmonary thromboembolism due to dead, dying, and deteriorating worms in the vascular circulation.

True in all treatment regimens, but a natural part of the disease clearing process.

Mitigated by exercise restriction and corticosteroids.

What recent research suggests about corticosteroid use in heartworm treatment?

Prednisone use may increase the risk of thromboembolism.

It can aggravate intimal disease, act as pro-coagulants, and reduce pulmonary blood flow, which is necessary to clear deteriorating worms and debris.

How does doxycycline help mitigate the complications of heartworm disease treatment?

Reduces the inflammatory response.

Mitigates pathological changes.

Renders microfilariae uninfective to mosquitoes.

What is the main disadvantage of the "Slow Kill" ivermectin approach?

Prolonged course of therapy with ongoing pathology and disease process.

Potential for facilitating emerging drug resistance.

What is the FDA-approved regimen for adulticide treatment in heartworm disease?

Melarsomine (Immiticide) is the only FDA-approved adulticidal treatment.

Efficacy: 96% of cases cleared without issue.

Regimen involves two injections 24 hours apart for Class 1 and Class 2 patients.

When is the FDA-approved 2-injection regimen for adulticide treatment typically recommended?

For animals diagnosed asymptomatically on routine screening, with normal blood chemistry, no radiographic anomalies, and no evidence of a significant heartworm burden.

What is the AHS/CAPC recommended regimen for adulticide treatment in heartworm disease?

Three injections of melarsomine (2.5 mg/kg, deep epaxial lumbar, SID).

First injection at Day 60 post-diagnosis, then two more injections 24 hours apart at Day 90 and Day 91.

What is the efficacy of the new "Slow Kill" regimen with doxycycline?

Efficacy of 78% at 36 weeks post-initial treatment.

Kills microfilariae by 12 weeks.

How does the Moxi-Doxy regimen compare to other "Slow Kill" treatments?

95.9% efficacy in eliminating adult heartworms.

Killed microfilariae by 21 days.

Considered a promising alternative, but not endorsed by AHS or CAPC.

What are the potential benefits of Moxi-Doxy as a treatment alternative?

Mitigates the pathogenic effects of Wolbachia.

Kills microfilariae by 21 days.

May be considered a legitimate alternative to traditional treatments.

Why is melarsomine (Immiticide) considered the gold standard in heartworm treatment?

FDA-approved and has a long history of proven efficacy (96% success rate).

The only FDA-approved adulticidal treatment for heartworms.

What are the key considerations for veterinarians when choosing a heartworm treatment regimen?

Treatment options should be considered based on the patient's clinical status, heartworm burden, and overall health.

A mix of efficacy, safety, and cost considerations should guide the choice of therapy.