DefendazoleTM — veterinary medication

Overview

Source: Animal Drugs @ FDA

Proprietary name

DefendazoleTM

Active ingredient

Fenbendazole

Application type

ANADA

Sponsor

Norbrook Laboratories, Ltd.

Applications on record

1

First published

February 2, 2026

Adverse event reports

Source: openFDA VeDDRA

4,228

Reports mentioning this ingredient

February 2, 1987 – March 25, 2026

593

Classified serious

per reporter assessment

896

Lack of expected efficacy

resistance signal

95

Human operator exposure

needle-stick or splash

Not a risk measure. Veterinary adverse event reports are influenced by how many animals are treated, reporting practice and product age. Reports do not establish that the product caused the event, and a single report can cover an entire herd or flock. Attribution here is by active ingredient because the source dataset redacts brand names.

Attributed by active ingredient “FENBENDAZOLE”. Green Book ingredient names and VeDDRA ingredient names do not always agree exactly, so attribution is approximate and labelled as such.

Reported reactions

Source: openFDA VeDDRA

Clinical signs coded in the VICH VeDDRA four-level hierarchy, most frequent first.

Reaction terms reported for this ingredient, by report count.
Reaction (VeDDRA term)	Reports	Relative frequency
Vomiting	949
Depression	526
Anorexia	505
Diarrhoea	467
Death	373
Accidental exposure	91
Ataxia	86
Vocalisation	82
Adipsia	77
Weakness	75
Bloody diarrhoea	74
Death by euthanasia	73
Hyperactivity	71
Unclassifiable adverse event	70
Trembling	65
Fever	62
Lack of efficacy (endoparasite) - tapeworm	62
Underfilling, Package	57
Convulsion	54
Digestive tract disorder NOS	52

Species affected

Source: openFDA VeDDRA

Dog 3,365 Cattle 204 Cat 154 Horse 98 Human 51 Goat 43 Pig 35 Sheep 13 Other 13 Other Birds 8 Chicken 4 Turkey 4

Regulatory context

Abbreviated New Animal Drug Application (ANADA). A generic animal drug demonstrating bioequivalence, pharmaceutical equivalence and identical manufacturing criteria to the pioneer application. Veterinary generics have no formal therapeutic-equivalence coding system; they match the pioneer NADA specification instead.

Extra-label use in food-producing animals is governed by the Animal Medicinal Drug Use Clarification Act of 1994 (AMDUCA) and 21 CFR Part 530. It requires a valid veterinarian-client-patient relationship and is prohibited outright for certain drug classes. Withdrawal times are determined by FARAD, not by this index.

Sources for this page

Animal Drugs @ FDA	FDA CVM	Applications, sponsor, status, withdrawal
Animal & Veterinary Events	FDA CVM	VeDDRA adverse event aggregates by active ingredient