Comparing compressed 2-dose and 3-dose melarsomine protocols in the era of adjunctive therapy: a randomized clinical trial of 168 dogs with heartworm disease.

A 2-dose melarsomine protocol with doxycycline, moxidectin, and prednisone is safe and effective for Class 1–2 heartworm disease.

This randomized clinical trial compared compressed 2-dose and 3-dose melarsomine protocols in 168 dogs with Class 1 or 2 heartworm disease, all receiving adjunctive doxycycline, sustained-release moxidectin, and prednisone. Dogs in the 2-dose group received melarsomine on days 14 and 15, while the 3-dose group received injections on days 14, 44, and 45. All dogs were exercise-restricted for 4 weeks following melarsomine administration, with daily clinical monitoring during this period. Antigen testing was performed 6 to 9 months post-treatment to assess efficacy. Of 165 dogs retested, antigen negativity rates were 95.3% (95% CI, 88.4%–98.7%) in the 2-dose group and 98.8% (95% CI, 93.2%–100%) in the 3-dose group, with no statistically significant difference between groups. However, the sample size was insufficient to confirm noninferiority at the predefined margin of 4%. Survival was 100% across both groups. Complications were uncommon; only 7 dogs required thoracic radiographs with or without additional treatment, and none required intensive care. Post-melarsomine cough, increased respiratory effort, and weakness were similarly rare between groups. The authors conclude that a compressed 2-dose melarsomine protocol combined with modern adjunctive therapy is safe and effective, and offers practical advantages over the standard 3-dose protocol by reducing treatment costs, required clinic visits, and overall treatment duration.

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