Clinical assessment of heartworm-infected Beagles treated with a combination of imidacloprid/moxidectin and doxycycline, or untreated.

Administration of moxidectin topically and doxycycline PO has been utilized experimentally as an alternative treatment for heartworm disease. However, clinical effects of this protocol remain poorly characterized. To evaluate the clinical and postmortem findings associated with administration of doxycycline and monthly 10% imidacloprid + 2.5% moxidectin (IMD + MOX, Advantage Multi/Advocate) to Dirofilaria immitis-experimentally infected as compared to nontreated control dogs. Sixteen purpose-bred, female, Beagle dogs. Prospective, blinded, experimental study. Animals with surgically transplanted adult heartworms were randomized into 2 study groups of equal size: a nontreated control group (n = 8) and an IMD + MOX and doxycycline-treated group (n = 8). Randomization was performed using a complete block design according to circulating microfilarial concentrations, measured before treatment. Serum biochemical profiles, CBCs, thoracic radiographs and echocardiograms were performed prior to and 3 weeks after transplantation, and monthly for 10 months. Postmortem gross and histopathologic evaluations were performed. Compared to control animals, mean ± SD serum alanine aminotransferase (181 ± 203 U/L vs 33 ± 7 U/L; P < .0001) and alkaline phosphatase (246 ± 258 U/L vs 58 ± 19 U/L; P < .0001) activities were significantly higher in the treated group on day 28. Radiographic and echocardiographic evidence of heartworm disease was observed in both groups; however, no significant differences in these variables were noted between groups. Mean ± SD pulmonary arterial thrombus score was significantly higher in the treated vs nontreated group (3.9 ± 0.4 and 1.5 ± 2.1, respectively; P = .01). The treatment protocol was well-tolerated with no clinically relevant adverse effects for any variable evaluated during the observational period.