Outcome of a heartworm treatment protocol in dogs presenting to Louisiana State University from 2008 to 2011: 50 cases

Since 2008, the American Heartworm Society has recommended using a three-dose melarsomine protocol (a single intramuscular injection of melarsomine dihydrochloride at 2.5 mg/kg, followed approximately 1 month later with two doses administered 24 h apart) for all heartworm-positive dogs, with doxycycline given at 10 mg/kg twice daily for 4 weeks prior to administration of melarsomine. To report the efficacy and side effects of this standard heartworm treatment protocol in 50 dogs presenting to our hospital from 2008 to 2011, information on the history, clinical, laboratory, and diagnostic imaging findings and treatment was obtained from medical records. When possible, additional follow-up information was obtained through telephone interviews with referring veterinarians and owners. Twenty-six dogs (52%) experienced minor complications, such as injection site reactions, gastrointestinal signs (vomiting, diarrhea, inappetance), and behavioral changes (lethargy, depression) during or after heartworm treatment. Twenty-seven dogs (54%) experienced respiratory signs (coughing, dyspnea) and heart failure attributed to progressive heartworm disease and worm death. Seven dogs (14%) died within the treatment period. Owners frequently reported behavioral changes, such as depression and lethargy, suspected to be secondary to pain. Fifty percent of owners surveyed indicated that, prior to the diagnosis, they either were not currently administering heartworm preventative, or they had recently adopted the dog from a shelter that did not administer preventatives. After treatment, 100% were administering heartworm preventatives to their pet. Eighteen dogs (36%) received a heartworm antigen test 6 months after adulticide therapy, 12 of which tested negative and six tested positive. Four of the dogs with a positive test at 6 months had negative tests 1 month later with no additional treatment. Adverse effects were common with the recommended protocol, but the majority of these were mild. Dogs in Class 1 (i.e., heartworm positive but otherwise largely lacking clinical evidence of disease) did not experience any major adverse effects or death.