Lack of efficacy (flea)
VeDDRA Code: 2649
8,320 adverse event reports referencing this reaction
Species Most Affected
Breeds Most Affected
Associated Drugs
Data Summary
| Metric | Value |
|---|---|
| Total reports referencing reaction | 8,320 |
| Reports with fatal outcome | 13 |
| Case-fatality rate (reported events) | 20.0% |
| Species observed | 4 |
| Breeds observed | 20 |
| Drugs associated with reaction | 20 |
Source: FDA Center for Veterinary Medicine — Adverse Event Reporting (CVM AER); reaction term coded under VeDDRA 2649.
Lack of efficacy (flea) Reaction Insights
The FDA Center for Veterinary Medicine database currently lists 8,320 adverse event reports that reference Lack of efficacy (flea) as a reaction term, including 13 reports with a death outcome — a 20.0% case-fatality figure calculated across only those events where this reaction was coded. The reaction is indexed in the openFDA system under VeDDRA code 2649, the standardized veterinary dictionary used to normalize clinical signs across submitters. Because reports are voluntary and often describe multiple concurrent signs per animal, the volume here reflects reporting intensity rather than true incidence in the broader pet population.
Lack of efficacy (flea) appears most frequently in reports for Dog (7,217 reports), Cat (1,095 reports), Unknown (5 reports) — with Dog dominating at 7,217 entries. Within those species, the breeds most often named alongside this reaction are Dog (unknown) (1,023), Crossbred Canine/dog (787), Chihuahua (630). These distributions are influenced both by underlying breed popularity and by how veterinarians and owners code a given clinical sign, so they should be interpreted as a reporting fingerprint rather than a pure susceptibility ranking.
The drugs most commonly co-reported with Lack of efficacy (flea) are Nitenpyram (1,803 reports), Milbemycin Oxime + Spinosad (1,591 reports), Fluralaner Chew Tablets (1,451 reports), Spinosad (1,081 reports), with Nitenpyram appearing alongside this reaction in 1,803 submissions. Co-reporting does not establish that any specific product caused the reaction — FDA CVM data captures temporal association only. The value of these aggregates is in flagging which therapeutic classes appear repeatedly alongside a given clinical sign, so owners and veterinarians can ask targeted questions about medications currently in use.
Source: FDA Center for Veterinary Medicine — Adverse Event Reports FDA Center for Veterinary Medicine — Adverse Event Reports Data reflects voluntary submissions and may not represent actual incidence rates
Read our methodology — how this data is sourced, computed, and verified.