Among the 1.34 million adverse-event reports in the FDA Center for Veterinary Medicine (CVM) openFDA database, dogs dominate by volume — but cats tell a distinctly different pharmacovigilance story. Dogs account for 974,175 reports (72.7% of the total); cats for 145,155 (10.8%). The roughly 6.7:1 dog-to-cat ratio reflects market size, prescription volume, and owner-reporting behavior rather than any inherent safety comparison.

But when you look past the volume and examine what the reports actually contain — the reactions, the drugs, and the outcomes — the profiles diverge in ways that matter to clinical practice.

This is a data analysis, not a clinical guide. Every number comes from a direct computation of the FDA CVM animal drug adverse-event database (analysis run date: 2026-06-09). Reports reflect suspected associations, not confirmed causalities.

Serious outcomes: cats fare worse

Fatal outcomes (Died or Euthanized) appear at markedly different rates:

Nearly one in ten cat reports ends in death or euthanasia, compared with roughly one in twenty for dogs. This is not proof that drugs are inherently more dangerous to cats. Several factors inflate the cat fatal-outcome rate: cats are presented to veterinarians later in the course of illness, they are more physiologically fragile in emergency settings, and adverse-event reports tend to be filed when the outcome is severe enough to warrant documentation. The data is also influenced by accidental toxicities (particularly permethrin exposure from dog products) that carry high fatality rates in cats.

Still, the magnitude of the gap — 9.5% vs 5.5% — is a reminder that the pharmacovigilance burden falls differently on feline patients.

Top reactions: where the species diverge

Dogs: parasiticide efficacy complaints dominate

The five most-reported reactions in dogs are:

Beyond gastrointestinal signs, lack-of-efficacy (LOE) reports are a defining feature of the dog data. Heartworm LOE accounts for 120,000+ reports (ineffective heartworm larvae plus heartworm endoparasite LOE combined), and flea LOE adds another 51,131. Hookworm LOE contributes 48,771. Together, LOE reports represent a substantial share of all dog reactions — reflecting the enormous prescription volume of heartworm and flea/tick preventives and the scrutiny they receive.

Seizures appear in 30,179 dog reports (3.1%), and elevated liver enzymes (ALT, SAP) collectively account for over 46,000 reports — a signature of the NSAID and anticonvulsant monitoring burden in dogs.

Cats: application-site reactions, anorexia, and behavioral signs

The cat reaction profile looks different:

Several patterns stand out:

1. Application-site reactions are a cat signature. Alopecia and hair loss at the application site together account for 16,796 reports (11.6% of all cat reports). Topical parasiticides — selamectin, fluralaner spot-on, imidacloprid — are the primary drivers. This reaction category is barely visible in dogs (dogs receive many parasiticides orally).

2. Anorexia is proportionally more prominent. At 7.4% of cat reports vs 4.7% for dogs, anorexia reflects the feline tendency toward food refusal under physiological stress — and its clinical significance in a species prone to hepatic lipidosis after even brief fasting.

3. Behavioral and neurological signs are overrepresented. Behavioral disorder (4.6%), hyperactivity (3.1%), and vocalization (2.9%) are all more prominent in the cat profile than in dogs. Ataxia appears at 4.5% in cats vs 2.4% in dogs. Cats' neurological sensitivity to certain drug classes (notably pyrethroids) is well documented and shows up here.

4. Death appears higher in the reaction list. "Death" is the 6th most common cat reaction (5.5%) vs 13th in dogs (2.9%). This aligns with the higher fatal-outcome rate discussed above.

5. Hypersalivation is a cat-distinguishing sign. At 4.2% of cat reports (6,072 reports), hypersalivation barely registers in the dog top 20. It is a classic feline response to oral medications, foul-tasting compounds, and nausea.

The active-ingredient gap

Dogs: oral parasiticides and NSAIDs

The dog ingredient list is dominated by oral parasiticides (spinosad, milbemycin oxime, ivermectin, pyrantel, afoxolaner) and the NSAID carprofen. Spinosad and milbemycin oxime together account for over 347,000 dog reports — largely driven by the palatability and efficacy reporting volume associated with combination heartworm/flea preventive products.

Carprofen at 45,853 reports reflects the long history and massive prescription volume of this NSAID in canine osteoarthritis. Oclacitinib maleate (the active ingredient in Apoquel) at 26,986 reflects the explosion of allergic dermatitis prescribing over the past decade.

Cats: topicals, monoclonal antibodies, and feline-specific drugs

The cat ingredient list tells a different drug-delivery story. Topical products dominate. Selamectin (a topical parasiticide), fluralaner spot-on, imidacloprid, and the selamectin-sarolaner combination are all topical or spot-on formulations. Cats are notoriously difficult to pill, and the market has responded with topical alternatives — which generate their own adverse-event profile (application-site alopecia, hair loss, hypersalivation from grooming the application site).

Frunevetmab (7,204 reports) is the anti-nerve-growth-factor monoclonal antibody for feline osteoarthritis pain (the active in Solensia, the first monoclonal antibody approved for any animal species). Its report volume is notable for a relatively new drug class and reflects both uptake and the concentrated reporting that accompanies new biologic therapies.

Cefovecin (5,542 reports) is the long-acting injectable cephalosporin (Convenia) widely used in cats for its injection-based convenience. Its adverse-event volume reflects the sheer number of feline infections treated with this single-dose alternative to daily oral antibiotics.

Buprenorphine (5,115 reports) and meloxicam (3,552 reports) round out the feline pain-management pharmacovigilance picture.

The permethrin signal

Permethrin toxicity in cats is one of the best-documented species-specific drug hazards in veterinary medicine. Cats lack efficient glucuronidation pathways, making them highly sensitive to pyrethroids and permethrin. Canine topical spot-on products containing 45–65% permethrin can be lethal to cats from even minimal exposure — a single drop, or grooming a recently treated dog.

In the FDA data, permethrin/pyrethroid exposure in cats is not captured as a standalone "permethrin" ingredient (as it is for dogs, where Permethrin appears with 613 reports as a standalone ingredient). Instead, cat permethrin exposure is embedded in combination-product strings — mixtures of imidacloprid, moxidectin, pyriproxyfen, and permethrin that represent multi-drug exposures, often in the context of accidental application or environmental contact.

The critical clinical point is not the report count but the severity: permethrin toxicosis in cats carries a high fatality rate, with clinical signs including tremors, seizures, hyperthermia, and collapse typically appearing within hours of exposure. Over 96% of exposed cats develop clinical signs in published case series. The FDA data captures this through the elevated neurological signs in cats (ataxia at 4.5%, seizures at 2.1%) and the disproportionate death rate — but the permethrin-specific signal is diffused across combination-product reports.

Outcome patterns: what happens after the event

The higher "Ongoing" rate in cats (23.1% vs 19.2%) may reflect the difficulty of resolving chronic conditions in a species that masks clinical signs and presents later. The low "Recovered with Sequela" rate in cats (0.5% vs 3.2%) could reflect either under-documentation or the reality that sequelae in cats are less commonly tracked in reporting.

What this data can and cannot tell you

This analysis is based on a passive reporting database. The limitations are significant:

• Reports are not causal proof. A cat that received selamectin and then vomited may have vomited for reasons unrelated to the drug.
• Market volume drives report volume. Spinosad leads the dog list not because it is the most dangerous drug, but because it is one of the most widely prescribed.
• Under-reporting is substantial. The FDA acknowledges that adverse events are significantly under-reported in veterinary medicine. The true incidence of any reaction is likely many times higher than what appears here.
• Species comparisons are not risk comparisons. A higher report count or a higher fatal-outcome rate does not mean a drug is riskier in one species than another — it means the reporting captured more of those outcomes.
• The cat data is sparser. With 145,155 reports vs 974,175 for dogs, the cat sample has more statistical noise, and individual reaction counts should be interpreted cautiously.

Despite these caveats, the species-level divergence in reaction profiles is clinically meaningful. Cats show more neurological and behavioral reactions, more application-site effects from topicals, higher anorexia rates, and a higher case-fatality proportion. Dogs show more LOE reports for parasiticides, more liver-enzyme elevations, and more NSAID-related monitoring signals. These are patterns that pharmacovigilance databases are designed to surface — and that the clinical community should track.

Sources

• FDA Center for Veterinary Medicine, Adverse Event Reporting System. openFDA Animal Drug Adverse Event API. Available at: https://open.fda.gov/apis/animalandveterinary/event/
• FDA CVM, "Adverse Event Reports for Animal Drugs and Devices." Available at: https://www.fda.gov/animal-veterinary/product-safety-information/adverse-event-reports-animal-drugs-and-devices
• Bates N. "Permethrin toxicosis in cats." Australian Veterinary Journal (2008). Available at: https://www.esccap.org/uploads/news/vv7u8ubv/Permethrin%20toxicosis%20in%20cats%20Austr%20Vet%20J%202008.pdf
• Richardson JA. "Permethrin spot-on toxicoses in cats." Journal of Veterinary Emergency and Critical Care (2000). PMC: https://pmc.ncbi.nlm.nih.gov/articles/PMC10822630
• EMA CVMP, "Veterinary Pharmacovigilance 2015 Public Bulletin." Available at: https://www.ema.europa.eu/en/documents/other/public-bulletin-veterinary-pharmacovigilance-2015_en.pdf
• FDA CVM, "Animal Drug Safety-Related Labeling Changes." Available at: https://www.fda.gov/animal-veterinary/drug-labels/animal-drug-safety-related-labeling-changes