What is the recommended treatment for heartworms?

Treatment of Heartworms in Dogs

The recommended treatment for heartworm disease in dogs is a three-dose melarsomine dihydrochloride protocol, combined with doxycycline and a macrocyclic lactone, as this approach provides the most effective clearance of adult worms while minimizing complications. 1, 2

Treatment Protocol Based on Disease Classification

Standard Treatment Protocol

• For Class 1 (mild) and Class 2 (moderate) heartworm disease: Administer melarsomine dihydrochloride 2.5 mg/kg IM twice, 24 hours apart, followed by a second treatment series 4 months later 1
• For Class 3 (severe) heartworm disease: Use the alternate dosing regimen - administer a single injection of melarsomine 2.5 mg/kg IM, then approximately 1 month later administer two more injections 24 hours apart 1
• All melarsomine injections must be administered deep intramuscularly in the lumbar muscles (L3-L5) using appropriate needle size (23 gauge for dogs ≤10 kg, 22 gauge for dogs >10 kg) 1

Adjunctive Therapy

• Administer doxycycline 10 mg/kg twice daily for 4 weeks prior to melarsomine treatment to target Wolbachia bacteria and improve treatment outcomes 2, 3
• Provide a macrocyclic lactone (such as moxidectin) monthly throughout treatment to eliminate susceptible larvae and prevent new infections 3, 4
• Consider adding prednisolone and clopidogrel for 1 week before treatment in microfilaremic dogs to reduce risk of adverse reactions 3

Management of Complications

• Respiratory signs (coughing, dyspnea) and heart failure may occur in approximately 54% of dogs during treatment due to worm death and should be managed appropriately 2
• Minor complications including injection site reactions, gastrointestinal signs, and behavioral changes (lethargy, depression) occur in about 52% of treated dogs 2
• Consider using butorphanol and dexamethasone just before melarsomine injections to reduce pain and inflammation 3
• For dogs at risk of pulmonary thromboembolism, anticoagulant therapy (such as dalteparin) may be administered for 10 days following melarsomine treatment 3

Treatment Efficacy and Follow-up

• Treatment efficacy should be assessed by heartworm antigen testing 4 months after treatment completion 1
• A successful treatment is defined as conversion from antigen-positive to antigen-negative status 1
• Some dogs may initially test positive at 6 months post-treatment but convert to negative by 7 months without additional treatment 2
• Clinical improvement should be observed gradually as the effects of heartworm infection resolve, though some chronic effects may not completely resolve 1

Alternative Treatment Options

• In situations where melarsomine is unavailable or financially inaccessible, a non-arsenical protocol using moxidectin and doxycycline ("moxi-doxy") can be considered 5
• This alternative regimen consists of doxycycline 10 mg/kg PO every 12-24 hours for 28 days combined with monthly topical moxidectin at label dose until antigen-negative status is achieved 5
• While less effective than the standard melarsomine protocol, this approach provides a viable alternative when arsenical treatment is not possible 5

Important Considerations

• Dogs should be stabilized prior to treatment, particularly those with Class 3 disease 1
• Exercise restriction is critical during and after treatment to minimize complications from worm death 2
• Heartworm preventative administration should be continued year-round following treatment to prevent reinfection 2
• The "susceptibility gap" (period when some worm stages are not susceptible to treatment) can be effectively addressed by combining the three-dose melarsomine protocol with continued macrocyclic lactone therapy 4