Table 4.

Safety, welfare, and population concerns regarding heartworm adulticide treatment in dogs, using moxidectin and doxycycline.

Concern	Rationale	Assessment
Pulmonary pathology	•Continued inflammatory response to the heartworms during prolonged death	•Lesser harm than leaving heartworms untreated •Mitigated by doxycycline •AHS 3-dose melarsomine protocol delays melarsomine until 60 days post-diagnosis (however some published evidence supports initiating melarsomine at 30 days post-diagnosis)
Exercise restriction	•Long period of exercise restriction until no antigen detected status is reached •Burden on owner, welfare concern for dogs	•Serious complications rare even without strict exercise restriction •More studies are needed to determine the optimal duration and extent of exercise restriction for moxi-doxy vs. melarsomine
Compliance with monthly medication	•Long duration of treatment •Treatment may be stopped by owner due to financial considerations, clinical improvement, limited access to medication	•Similar issues for preventives, which are also needed for these dogs post-treatment •Sustained release formulations offer a solution; more data needed for efficacy and optimal dosage regimen
Maintenance of a reservoir of infection	•Adults remain alive for extended period	•Lesser harm than leaving heartworms untreated •Moxidectin quickly clears microfilariae, breaking transmission cycle •Treatment may also interrupt transmission before death of adult worms through effects on embryogenesis and larval viability
Selection for microfilarial resistance	•Long duration of low concentrations of moxidectin may select for resistance	•Evidence suggests that moxidectin may be effective against resistant microfilariae •This concern also exists with year-round preventives, given known compliance issues
Ultimate cost savings may not be significant	•Long duration of treatment may cancel the cost savings of the non-arsenical protocol •Long length of stay and time in care is also a significant concern for shelters and rescues	•Offering a spectrum of care approach and payment plans can reduce costs and make melarsomine more accessible •Clear communication about total costs, including clinic visits, medication and testing, is required •Barrier may be up-front cost, not total cost •Melarsomine may be refused for reasons other than financial