Oxfendazole (Ref: HOE 8105)

Oxfendazole (Ref: HOE 8105)	Last updated: 15/09/2025
(Also known as: OFDZ; RS-8858)

GENERAL INFORMATION

Description

A benzimidazole anthelmintic active against both adults and laval stages of parasitic worms

Examples of veterinary uses

Used for the management roundworms, strongyles and pinworms

Examples of species treated

Sheep; Cattle; Goats; Pigs; Horses

Approval status

VMR 2013/2033 approval status (GB/UK)

Approved - usually avilable as a prescription only medicine to be authorised by suitably qualified person (POM-VPS)

EU Regulatory approval status

Approved

Chemical structure

Isomerism

Oxfendazole exhibits enantiomeric isomerism, meaning it exists as (+)-oxfendazole and (–)-oxfendazole enantiomers. These isomers differ in the spatial arrangement around the chiral centre in the benzimidazole ring system, which can influence their pharmacokinetics and biological activity. Commercially available oxfendazole is typically a racemic mixture.

Chemical formula

C₁₅H₁₃N₃O₃S

Canonical SMILES

COC(=O)NC1=NC2=C(N1)C=C(C=C2)S(=O)C3=CC=CC=C3

Isomeric SMILES

No data

International Chemical Identifier key (InChIKey)

BEZZFPOZAYTVHN-UHFFFAOYSA-N

International Chemical Identifier (InChI)

InChI=1s/C15H13N3O3S/c1-21-15(19)18-14-16-12-8-7-11(9-13(12)17-14)22(20)10-5-3-2-4-6-10/h2-9H,1H3,(H2,16,17,18,19)

2D structure diagram/image available?

Yes

General status

Veterinary substance type

Anthelmintic, Antiparasitic

Substance groups

Benzimidazole

Minimum active substance purity

Known relevant impurities

Substance origin

Synthetic

Mode of action

Inhibits tubulin synthesis in the parasite and leading to death by starvation.

Molecular targets

[Tubulin beta chain, Antagonist]

CAS RN

53716-50-0

EC number

258-714-5

CIPAC number

US EPA chemical code

PubChem CID

Therapeutic Class

Antiparasitic products, insecticides & repellents: Anthelmintics

ATCvet Code

QP52AC02

Controlled Drug?

Regulation 37/2010 MRL Classification

Allowed substance (Table 1: Ruminants, Porcine, Equidae)

Molecular mass

315.35

PIN (Preferred Identification Name)

IUPAC name

(5-(phenylsulfinyl)-1H-benzimidazol-2-yl)carbamic acid methyl ester

CAS name

methyl-5-(phenylsulfinyl) benzimidazole-2-carbamate

Forever chemical

Other status information

Relevant Environmental Water Quality Standards

Physical state

White to off-white powder

Commercial

Property

Value

Availability status

Current

Introduction & key dates

Circa 1980, registered for veterinary use USA

Example manufacturers & suppliers of products using this active now or historically

Syntex Animal Health
Zoetis UK Ltd
Chanelle Animal Health Ltd
Norbrook Laboratories Ltd

Example products using this active

Autoworm Finisher
Autoworm First Grazer Pulsatile-Release Intraruminal Device
Bovex Oral Suspension

Formulation and application details

Available in a variety of formulations including pour-ons, drenches, oral suspensions and pulsatile-release intraruminal devices

Commercial production

The production of oxfendazole involves the oxidation of fenbendazole, a structurally related benzimidazole compound. The process begins with fenbendazole, which contains a phenylthio group, undergoing a controlled oxidation using hydrogen peroxide in the presence of a strong, non-oxidising mineral acid and a C₁–C₆ aliphatic alcohol as a solvent or co-solvent. This reaction selectively converts the phenylthio group into a phenylsulfinyl moiety, yielding oxfendazole.

Impact on climate of production and use

Published GHG data is not available for most pharmaceuticals. However, according to industry, global averages suggest producing 1 kg of a typical active pharmaceutical ingredient can range from 10 to 100 kg CO₂e for small molecule drugs and potentially up to 1000 kg CO₂e for complex biologicals such as vaccines, depending on the drug type, its formulation, complexity of synthesis, solvent recovery, and energy sources used.

ENVIRONMENTAL FATE

Property

Value

Source; quality score; and other information

Interpretation

Solubility - In water at 20 °C (mg l⁻¹)

3.11

Low

Solubility - In organic solvents at 20 °C (mg l⁻¹)

Melting point (°C)

245

Boiling point (°C)

Degradation point (°C)

Flashpoint (°C)

Octanol-water partition coefficient at pH 7, 20 °C

8.91 X 10⁰¹

Calculated

Log P

1.95

Low

Fat solubility of residues

Solubility

Data type

Density (g ml⁻¹)

Dissociation constant pKa) at 25 °C

Vapour pressure at 20 °C (mPa)

Henry's law constant at 25 °C (Pa m³ mol⁻¹)

Volatilisation as max % of applied dose lost

From plant surface

From soil surface

Maximum UV-vis absorption L mol⁻¹ cm⁻¹

Surface tension (mN m⁻¹)

Refractive Index

Environmental release

Main environmental release is via the slurry and manure from treated livestock

Degradation

Property

Value

Source; quality score; and other information

Interpretation

Soil degradation (days) (aerobic)

DT₅₀ (typical)

DT₅₀ (lab at 20 °C)

DT₅₀ (field)

DT₉₀ (lab at 20 °C)

DT₉₀ (field)

Note

Manure DT₅₀ (days)

Aqueous photolysis DT₅₀ (days) at pH 7

Value

Note

Aqueous hydrolysis DT₅₀ (days) at 20 °C and pH 7

Value

Note

Water-sediment DT₅₀ (days)

Water phase only DT₅₀ (days)

Sediment phase only DT₅₀ (days)

Air degradation

As this parameter is not normally measured directly, a surrogate measure is used: ‘Photochemical oxidative DT₅₀’. Where data is available, this can be found in the Fate Indices section below.

Decay in stored produce DT₅₀

Soil adsorption and mobility

Property

Value

Source; quality score; and other information

Interpretation

Linear

K_d (mL g⁻¹)

8.87

Slightly mobile

K_oc (mL g⁻¹)

885

Notes and range

USEPA data: K_d range 3.87-16.73 mL g⁻¹, K_oc range 470-1673 mL g⁻¹, Soils=3

Freundlich

K_f (mL g⁻¹)

8.87

Slightly mobile

K_foc (mL g⁻¹)

887

¹/_n

0.9

Notes and range

USEPA data: K_f range 4.5-15.7 mL g⁻¹, K_foc range 544-1570 mL g⁻¹, ¹/_n range 0.87-0.93, Soils=3

pH sensitivity

Fate indices

Property

Value

Source; quality score; and other information

Interpretation

GUS leaching potential index

Bio-concentration factor

BCF (l kg⁻¹)

CT₅₀ (days)

Known soil and groundwater metabolites

None

Other known metabolites

Metabolite name and reference

Aliases

Formation medium / Rate

Estimated maximum occurrence fraction

2-amino-5(6)-phenylsulfinyl benzimidazole

oxfendazole amine

Hydrolysis

ECOTOXICOLOGY

Terrestrial ecotoxicology

Property

Value

Source; quality score; and other information

Interpretation

Mammals - Acute oral LD₅₀ (mg kg⁻¹)

> 6400

Rat

Low

Mammals - Short term dietary NOEL

(mg kg⁻¹)

(ppm diet)

Mammals - Chronic 21d NOAEL (mg kg⁻¹ bw d⁻¹)

Birds - Acute LD₅₀ (mg kg⁻¹)

Birds - Short term dietary (LC₅₀/LD₅₀)

Birds - Chronic 21d NOEL (mg kg⁻¹ bw d⁻¹)

Earthworms - Acute 14 day LC₅₀ (mg kg⁻¹)

Earthworms - Chronic NOEC, reproduction (mg kg⁻¹)

> 971

Eisenia foetida

Low

Soil micro-organisms

Collembola

Acute LC₅₀ (mg kg⁻¹)

Chronic NOEC (mg kg⁻¹)

Non-target plants

Vegetative vigour ER₅₀ (g ha⁻¹)

Seedling emergence ER₅₀ (g ha⁻¹)

Honeybees (Apis spp.)

Contact acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Oral acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Unknown mode acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Chronic

Notes

Bumblebees (Bombus spp.)

Contact acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Oral acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Mason bees (Osmia spp.)

Contact acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Oral acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Other bee species (1)

Acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg insect⁻¹)

Mode of exposure

Other bee species (2)

Acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg insect⁻¹)

Mode of exposure

Beneficial insects (Ladybirds)

Beneficial insects (Lacewings)

Beneficial insects (Parasitic wasps)

Beneficial insects (Predatory mites)

Beneficial insects (Ground beetles)

Aquatic ecotoxicology

Property

Value

Source; quality score; and other information

Interpretation

Temperate Freshwater Fish - Acute 96 hour LC₅₀ (mg l⁻¹)

> 2.7

Lepomis macrochirus

Moderate

Temperate Freshwater Fish - Chronic 21 day NOEC (mg l⁻¹)

Tropical Freshwater Fish - Acute 96 hour LC₅₀ (mg l⁻¹)

> 5.6

Danio rerio EC₅₀ Embryo

Moderate

Temperate Freshwater Aquatic invertebrates - Acute 48 hour EC₅₀ (mg l⁻¹)

1.17

Daphnia magna

Moderate

Temperate Freshwater Aquatic invertebrates - Chronic 21 day NOEC (mg l⁻¹)

Tropical Freshwater Aquatic invertebrates - Acute 48 hour EC₅₀ (mg l⁻¹)

Aquatic crustaceans - Acute 96 hour LC₅₀ (mg l⁻¹)

Sediment dwelling organisms - Acute 96 hour LC₅₀ (mg l⁻¹)

Sediment dwelling organisms - Chronic 28 day NOEC, static, water (mg l⁻¹)

Sediment dwelling organisms - Chronic 28 day NOEC, sediment (mg kg⁻¹)

Aquatic Plants (free-floating, fonds growth, fresh) - 7 day (mg l⁻¹)

Aquatic plants (rooted, growth rate, fresh) - 14 day (mg l⁻¹)

Algae - Acute (growth rate, fresh; mg l⁻¹)

Algae - Chronic (growth rate, fresh; mg l⁻¹)

Mesocosm study data

NOEAEC mg l⁻¹

Marine bivalves

HUMAN HEALTH AND PROTECTION

General

Property

Value

Source; quality score; and other information

Interpretation

Threshold of Toxicological Concern (Cramer Class)

High (class III)

Mammals - Acute oral LD₅₀ (mg kg⁻¹)

> 6400

Rat

Low

Mammals - Dermal LD₅₀ (mg kg⁻¹ body weight)

Mammals - Inhalation LC₅₀ (mg l⁻¹)

Other Mammal toxicity endpoints

ADI - Acceptable Daily Intake (mg kg⁻¹ bw day⁻¹)

ARfD - Acute Reference Dose (mg kg⁻¹ bw day⁻¹)

AAOEL - Acute Acceptable Operator Exposure Level (mg kg⁻¹ bw day⁻¹)

AOEL - Acceptable Operator Exposure Level - Systemic (mg kg⁻¹ bw day⁻¹)

Dermal penetration studies (%)

Dangerous Substances Directive 76/464

Exposure Routes

Public

Occupational

Mammalian dose elimination route and rate

Metabolised to active oxfendazole sulfoxide and sulfone. Excreted mainly in faeces.

Health issues

Specific human health issues

Carcinogen

Genotoxic

Endocrine disruptor

; ; ; ;

No data found

Reproduction / development effects

Acetyl cholinesterase inhibitor

Neurotoxicant

No data found

Respiratory tract irritant

Skin irritant

Skin sensitiser

No data found

Eye irritant

Phototoxicant

No data found

General human health issues

No further information available

Handling issues

Property

Value and interpretation

General

No information available

CLP classification 2013

WHO Classification

Not listed (Not listed)

UN Number

Waste disposal & packaging

Shelf-life, storage, stability and reactivity

TRANSLATIONS

Language

Name

English

oxfendazole

French

oxfendazole

German

Danish

Italian

Spanish

oxfendazol

Greek

Polish

Swedish

Hungarian

Dutch

Norwegian

Record last updated:	15/09/2025
Contact:	aeru@herts.ac.uk
Please cite as:	Lewis, K.A., Tzilivakis, J., Warner, D. and Green, A. (2016) An international database for pesticide risk assessments and management. Human and Ecological Risk Assessment: An International Journal, 22(4), 1050-1064. DOI: 10.1080/10807039.2015.1133242