The American Heartworm Society (AHS) three-dose melarsomine dihydrochloride protocol combined with doxycycline and a macrocyclic lactone is the recommended treatment for class III canine heartworm disease. The protocol applies to classes 1 through 3 disease without caval syndrome, and all dogs treated with this regimen in one multicenter cohort survived treatment and became antigen-negative on long-term follow-up. Journal of Smal…

Pretreatment stabilization precedes adulticide therapy in class III dogs. Class III disease carries greater cardiopulmonary compromise, and inflammatory and hemostatic markers — including D-dimer, C-reactive protein, interleukin-6, and cardiac troponin I — are elevated above the reference range at diagnosis in class III dogs and remain at pathological levels longer than in class I or II dogs during treatment. Parasites and V… Monitoring these markers during treatment is beneficial for predicting clinical outcomes and complications associated with melarsomine. Parasites and V…

Doxycycline is administered at 10 mg/kg PO q12h for 28 days to reduce Wolbachia burden prior to adulticide therapy. Parasites and V…+1 At this dose, all dogs achieve Wolbachia DNA negativity by 28 days post-treatment. Parasites and V… Gastrointestinal side effects are more frequent at 10 mg/kg BID than at lower doses, though the 10 mg/kg BID regimen provides the most complete Wolbachia elimination. Parasites and V…

Melarsomine dihydrochloride is administered as three injections at 2.5 mg/kg IM using the split-dose protocol: a single injection on day 1, followed by two injections given 24 hours apart beginning 30 days later. Parasites and V…+1 Sedation to facilitate injection and application of ice at the injection site are used in a subset of patients to improve tolerability. Journal of Smal… After each adulticide injection, hospitalization with cage rest is standard; median hospitalization time is 12 hours (range 6–48 hours). Journal of Smal…

A macrocyclic lactone preventive is administered concurrently throughout the treatment period to eliminate susceptible larvae and prevent new infections. Vector-Borne an…+1 The slow-kill method — long-term macrocyclic lactone monotherapy — is not recommended as a substitute for melarsomine-based treatment, as it has a longer time-to-effect that allows continued cardiopulmonary damage, and antigen clearance in class III dogs using the slow-kill method is poor. Journal of Vete…+1 Antigenemia cleared in only 1 of 4 class III dogs at the end of slow-kill therapy and remained cleared in only 1 of 4 class III dogs at 10 months. Veterinary Para…

Treatment-related side effects with the AHS protocol are rare and mild. Across classes 1–3, side effects included depression/lethargy in 4 of 35 dogs, cough in 2 of 35 dogs, and lameness, pain, or gastrointestinal signs in 1 of 35 dogs each; all resolved without additional supportive therapy. Journal of Smal… Pulmonary thromboembolism from dying worms is the primary serious complication, and strict exercise restriction is a mandatory component of the protocol — exercise restriction is included in the treatment approach by 80% of practitioners. Journal of the…

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