Adulticide treatment with melarsomine: outcome in 283 heartworm-positive dogs in Germany

BACKGROUND: Heartworm disease is of increasing significance in Europe because of climate change and the movement of dogs from endemic regions. Despite guidelines from the American Heartworm Society (AHS) and the European Society of Dirofilariosis and Angiostrongylosis (ESDA), some clinicians favor macrocyclic lactones and doxycycline alone, partly because of concerns about melarsomine complications. Recent studies, however, support the safety and efficacy of the recommended protocol. METHODS: This retrospective study analyzed the outcomes of dogs with Class I-III heartworm disease that underwent melarsomine adulticide treatment at a German referral center. Demographic, clinical, diagnostic, therapeutic, and outcome data, including adverse events, were systematically retrieved. Diagnosis was confirmed by antigen testing, with heat treatment applied when indicated. Therapy consisted of 28 days of doxycycline and monthly macrocyclic lactones, followed by a three-dose melarsomine protocol as recommended by AHS/ESDA. Supportive care included sedation, intravenous fluids, maropitant, and additional medications as clinically indicated. RESULTS: A total of 283 dogs were included. Median age was 4.2 years (range: 8 months-11.5 years), and median body weight was 19 (range: 3.4-51.1) kg. Females comprised 53% (84% spayed) and males 45% (89% neutered). All dogs originated from endemic European countries. Clinical signs before treatment included respiratory symptoms (31%), exercise intolerance (15%), gastrointestinal signs (8.5%), and others (2%), while 53% were asymptomatic. Complications following melarsomine were generally mild: injection-site soreness (9.2% after first, 2.1% after third injection), gastrointestinal signs (3.5% after first, 0.7% after third injection), and coughing (12.7% after first, 5.3% after third injection). Two dogs (0.7%) died during treatment, one from cardiac arrest under anesthesia and one from pancytopenia, but neither was conclusively attributable to melarsomine. At 6-month follow-up, none of the 221 dogs tested remained antigen positive. CONCLUSIONS: Adulticide treatment with melarsomine showed high efficacy and an acceptable safety profile. Most adverse events were mild and self-limiting, with rare severe complications. These findings support the use of evidence-based, guideline-driven protocols to manage heartworm disease in dogs living in European countries.