Extended-Duration Ectoparasiticides and Heartworm Prevention


A recent study examined whether the use of an extended-duration flea and tick product led to lapses in monthly dosing of heartworm medication.


According to recent studies, nearly all veterinarians in the United States recommend year-round flea and tick protection for pet dogs and cats, yet owner compliance is poor. In response, some ectoparasiticide products, such as fluralaner (Bravecto, Merck Animal Health), now offer extended coverage lasting 12 weeks and, therefore, require relatively infrequent dosing.

In a recent study published in Parasites & Vectors, investigators at Merck used purchase data of various heartworm and flea/tick preventives to examine treatment patterns for pet dogs in the United States. They also compared heartworm prevention practices when dog owners chose to administer monthly vs extended-duration flea/tick preventives.


The investigators used an infomining program (Vet Informatics) to collect data on owner purchases of flea/tick and heartworm medications from participating veterinary clinics. They focused specifically on transactions at approximately 650 veterinary clinics from June 2014, when Bravecto first became commercially available, through November 2017. Only purchases made for individual dogs 6 months and older were included in the study.


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Although records were anonymized, the investigators also recorded pet signalment information, then assigned a unique ID to each dog and recorded the number of preventive doses purchased over a 12-month period. Based on duration of action (1 vs 3 months), flea/tick medications were then divided into 2 categories for statistical analysis.


Vet Informatics data were retrieved for a total of 202,550 dogs, including 56,756 receiving fluralaner and 145,794 receiving a monthly flea/tick preventive. Dogs averaged 5.6 years in age and 18.0 kg in weight.

On average, dog owners administering fluralaner purchased 7.35 months of heartworm preventive per year, while those administering monthly flea/tick products purchased an average of 7.13 months of heartworm preventive per year. This difference was not considered clinically relevant, but rather indicated that heartworm prevention measures were similar for both groups of dogs, regardless of which flea/tick preventive was chosen. The monthly distribution of coverage was also similar between the 2 groups. For example, about 20% of dogs in each group received 6 months of heartworm coverage per year, whereas approximately 30% in each group received a full 12 months of coverage.

The investigators acknowledged that the study had 1 major limitation: They assumed that purchase of multiple medication doses indicated that all were administered on time at home. Purchase history, they said, is “an imperfect substitute for the number of doses that a pet actually gets” and instead reflects the maximum possible number of doses given within the time period. Regardless, the results suggest that using preventive medications with different dosing schedules does not negatively impact owner compliance.

Take-Home Message

Clinic transactional records indicated that owners purchased, on average, roughly 7 months of heartworm preventive per year for pet dogs. Heartworm prevention coverage was similar for pets receiving monthly and extended-duration ectoparasiticides.

Dr. Stilwell received her DVM from Auburn University, followed by a MS in fisheries and aquatic sciences and a PhD in veterinary medical sciences from the University of Florida. She provides freelance medical writing and aquatic veterinary consulting services through her business, Seastar Communications and Consulting.

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