Drug profile

The FDA adverse-event record for Leflunomide

18 FDA reports name Leflunomide, a lower-volume drug in the CVM extract. Species, reactions, and outcomes follow.

#1918 of 2,679
by report volume (all drugs)
18
adverse-event reports
27.8%
death-coded share
Dog
most-reported species
Verify with FDA CVM →

Corpus placement

According to the FDA Center for Veterinary Medicine openFDA adverse-event extract, Leflunomide ranks #1884 of 2679 by total reports (18). Death-coded-share rank requires at least 50 reports. National dual: Milbemycin Oxime + Spinosad is #1 of 2679 drugs by total adverse-event reports (149,624) at death-coded-share rank 965 of 1130 drugs with at least 50 reports (2.3%); separately, Atlantic Salmon Transgenic Whole (Opafp-Ghc2 Rdna Construct Inserted Into The A-Locus In The Eo-1A Lineage) is #1 highest death-coded share at 97.8% (report rank #821).

149,624
Milbemycin Oxime + Spinosad reports (#1)
97.8%
Atlantic Salmon Transgenic Whole (Opafp-Ghc2 Rdna Construct Inserted Into The A-Locus In The Eo-1A Lineage) death share (#1)
#1884
This drug, reports of 2679

Report volume reflects how common a breed or drug is and how often owners and vets file — not actual risk. Death-coded share ranks are limited to entries with enough reports to be meaningful. The two maps do not agree at #1.

Release-over-release change

What changed in the latest FDA data snapshot

PlainBreed reconstructed the prior snapshot from dated openFDA partitions through 2025 Q4, then compared it with the 2026-07-27 openFDA export. Leflunomide has 18 reports now versus 17 in that prior snapshot: 1 more (5.9%).

Report change
+1
Death-coded reports
+0
Death-coded share
−1.6 pts

This compares reported-event counts in two source snapshots. It does not establish a change in real-world risk, product safety, or disease incidence.

Subscribe to Leflunomide changes

Signature read: Leflunomide's 27.8% death-coded share is among the highest in the openFDA drug corpus.

Important: Adverse event reports do not establish that a drug caused or contributed to the event. Consult your veterinarian before making treatment decisions.
18
Total Reports
5
Deaths Reported
27.8%
Death-coded share of reports

Active Ingredients

Leflunomide

Administration Routes

OralUnknown

Species Affected

Dog 17
Human 1

Most Affected Breeds

Chihuahua 3
Crossbred Canine/dog 2
Shepherd Dog - Anatolian 1
Shih Tzu 1
Pug 1
Shepherd Dog - Australian 1
Spaniel - Springer English 1
Catahoula Leopard Dog 1
Cattle Dog (unspecified) 1
Terrier - Jack Russell 1

Most Reported Reactions

Vomiting 6
Anaemia NOS 5
Lethargy (see also Central nervous system depression in 'Neurological') 5
Anorexia 4
Diarrhoea 4
Death by euthanasia 3
Thrombocytopenia 3
Leucocytosis NOS 3
Weight loss 3
Medication error NOS 3
Splenomegaly 2
Fever 2

Outcome Breakdown

Ongoing
6 (33.3%)
Recovered/Normal
5 (27.8%)
Died
3 (16.7%)
Euthanized
2 (11.1%)
Outcome Unknown
2 (11.1%)

Leflunomide: high death-coded share in the FDA AER row

Read these counts as reporting volume, not risk: per our methodology, a widely-prescribed drug will rack up more raw FDA reports in a given year than a rarely-used one at an identical true rate, so we recommend comparing within similar-exposure products rather than across the full 2025 catalog.

What to do with this drug

A report does not prove a drug caused the reaction; consult a veterinarian before acting on this data.

Source: FDA Center for Veterinary Medicine openFDA Animal & Veterinary Adverse Events (CVM AER) · 2025

openFDA Animal & Veterinary Adverse Events (FDA CVM) for Leflunomide (#1918 of 2,679 by report volume); death-coded 27.8%. PlainBreed drug row · death-coded share stamp 27.8% · vintage 2025.

Informational only. FDA adverse-event reports are voluntary and do not prove causation; consult a veterinarian before acting on them. Verify with FDA CVM →