Evaluation of efficacy of heartworm preventive products at the FDA

The Center for Veterinary Medicine, U.S. Food and Drug Administration (FDA/CVM) has authority under the United States Code 21 under Section 514.80 to monitor for adverse experiences of approved animal products. Although veterinarians voluntarily report suspect drug-related events to manufacturers, firms that market FDA-approved animal products must report serious events to the FDA within 15 working days of the veterinarian or pet-owner's call to them. Under the present regulations, canine heartworm preventatives are approved for 100% efficacy after testing in laboratory and field conditions. The report of lack of efficacy against heartworm larvae is a serious adverse drug event because the resulting condition or the treatment of the condition is life threatening. Information on lack of effect that are deemed possibly, probably, or definitely drug-related available for review under generic product on the FDA/CVM website Surveillance of these reports indicates there are some failures for virtually all heartworm prevention product categories. Most failures have been reported in heartworm-endemic states. At this time, it is unclear whether these are representative of the rare occurrences of failure that have been in existence for a long time, but not reported regularly or promptly, or whether there is a true increase in complaints of ineffectiveness and real variability between products. This paper discusses methods, personnel, and procedures in place in the Division of Surveillance that will aid the FDA to better assess heartworm preventive treatment failures. It discusses scoring paradigms presently utilized by FDA/CVM to assess severity of complaints of lack of efficacy against heartworms, and welcomes audience input as to how to improve existing processes. Results suggest that more comprehensive reporting will provide FDA/CVM more accurate surveillance information regarding efficacy problems. Such practices will permit FDA/CVM to better interpret both incidence and severity of in-effect and possible patterns of emerging resistance and to convey this in any necessary updated labeling. It also indicates that as part of that process, practitioners should return to a more conservative testing schedule.