It happens. It happens a lot. Here are your best practices when a lapse in heartworm preventive delivery occurs.
(Photo courtesy of the American Heartwom Society)
Q. My client says she missed a dose of her dog's heartworm preventive. What now?
Dr. Clarke AtkinsA. While heartworm preventives are highly effective and convenient for clients to give, compliance persists as a problem in veterinary practices. Even the most conscientious client can miss a dose now and then, while other clients have much longer lapses.
Unfortunately, there's no one-size-fits-all answer to this question. Instead, veterinarians should consider the following questions:
The reason for these questions is that time and place have a great impact on heartworm risk. The risk, for instance, is much less when a monthly preventive is missed one time in Ohio in February than when a three-month lapse occurs at that same location in the summer. Likewise, just a two-week lapse in summer can result in infection in the Mississippi Delta.
Macrocyclic lactones provide a safety net know as “reach-back” or “retroactive efficacy,” when given continuously for at least 12 months. The length of the reach-back varies by product, with all products proven to be about 95% efficacious against nonresistant strains in the laboratory when given for at least 12 consecutive months after lapse. This protective benefit can be useful but should not be relied upon as part of routine heartworm prevention.
Another important compound is doxycycline, which can be administered as monotherapy at 10 mg/kg twice daily for 30 days to kill L3 and L4 larvae-it even kills immature adults that have escaped or will escape macrocyclic lactone prevention.1
Recommendations for treatment lapses
In all instances, preventive therapy should be administered on a year-round basis, both for the animal's protection and to help ensure improved compliance in the future.
1. McCall JW, Kramer L, Genchi C, et al. Effects of doxycycline on early infections if Dirofilaria immitis in dogs. Vet Parasitol 2011;176:361-367.
2. Chandrashekar R, Beall MJ, Saucier J, et al. Experimental Dirofilaria immitis infection in dogs: effects of doxycycline and Advantage Multi administration on immature adult parasites. Vet Parasitol 2014;206:93-98.
This question and others are the focus of a new series of 15-minute recorded talks designed to offer practical information on heartworm prevention, diagnosis and treatment. The “Eye on Heartworm” videos, which are made available by the American Heartworm Society, can be found at https://www.heartwormsociety.org/veterinary-resources/veterinary-education/videos.