Estradiol benzoate

Estradiol benzoate	Last updated: 15/09/2025
(Also known as: oestradiol benzoate)

GENERAL INFORMATION

Description

A semisynthetic estrogenic hormone with veterinary applications

Examples of veterinary uses

Mainly used as a hormone replacement therapy in conditions of inadequate estrogen production

Examples of species treated

Horses; Cattle; Cats; Dogs

Approval status

VMR 2013/2033 approval status (GB/UK)

Not approved

EU Regulatory approval status

Not approved

Chemical structure

Isomerism

Estradiol exhibits stereoisomerism, primarily due to the configuration of its hydroxyl groups and the orientation of its steroid backbone. The most biologically active form is 17beta-estradiol, where the hydroxyl group at carbon 17 is in the beta position. Its stereoisomer, 17alpha-estradiol, has the hydroxyl group in the alpha position and is significantly less potent in estrogenic activity. Additionally, estradiol can undergo glucuronidation at either the 3-hydroxyl or 17-hydroxyl positions, forming estradiol-3-glucuronide and estradiol-17-glucuronide, which are regioisomers with distinct metabolic pathways and biological roles. The benzoate esterification at the C3 hydroxyl group does not introduce additional isomerism.

Chemical formula

C₂₅H₂₈O₃

Canonical SMILES

CC12CCC3C(C1CCC2O)CCC4=C3C=CC(=C4)OC(=O)C5=CC=CC=C5

Isomeric SMILES

C[C@]12CC[C@H]3[C@H]([C@@H]1CC[C@@H]2O)CCC4=C3C=CC(=C4)OC(=O)C5=CC=CC=C5

International Chemical Identifier key (InChIKey)

UYIFTLBWAOGQBI-BZDYCCQFSA-N

International Chemical Identifier (InChI)

InChI=1S/C25H28O3/c1-25-14-13-20-19-10-8-18(28-24(27)16-5-3-2-4-6-16)15-17(19)7-9-21(20)22(25)11-12-23(25)26/h2-6,8,10,15,20-23,26H,7,9,11-14H2,1H3/t20-,21-,22+,23+,25+/m1/s1

2D structure diagram/image available?

Yes

Cambridge Crystallographic Data Centre diagrams

Common Name	Relationship	Link
estradiol	Parent
estradiol benzoate	-

General status

Veterinary substance type

Medicinal drug, Hormone

Substance groups

Steroid hormone

Minimum active substance purity

Known relevant impurities

Substance origin

Semi-synthetic

Mode of action

Substance binds to its specific intracellular receptor and regulates DNA transcription for protein formation

Molecular targets

[Estrogen receptor alpha, Agonist], [Estrogen receptor beta, Agonist], [Beclin-1, Binder], [ATP synthase subunit a, Inhibitor], [Nuclear receptor subfamily 1 group I member 2, Binder], [Neuronal acetylcholine receptor subunit alpha-4, Binder], [G-protein coupled estrogen receptor 1, Binder]

CAS RN

50-50-0

EC number

200-043-7

CIPAC number

US EPA chemical code

PubChem CID

222757

Therapeutic Class

Estrogens: Natural and semisynthetic estrogens, plain

ATCvet Code

QG03CA03

Controlled Drug?

Regulation 37/2010 MRL Classification

Molecular mass

376.5

PIN (Preferred Identification Name)

IUPAC name

[(8R,9S,13S,14S,17S)-17-hydroxy-13-methyl-6,7,8,9,11,12,14,15,16,17-decahydrocyclopenta[a]phenanthren-3-yl] benzoate

CAS name

Forever chemical

Other status information

Relevant Environmental Water Quality Standards

Physical state

White crystalline powder

Related substances & organisms

estradiol

estradiol cyprionate

ethinyl estradiol

Commercial

Property

Value

Availability status

Current

Introduction & key dates

Mid 1990s, introduced

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

Huabang Veterinary Pharmaceuticals China

Example products using this active

Estradiol Benzoate Injection
Estroject

Formulation and application details

Usually supplied as a injectable solution

Commercial production

The commercial synthesis of estradiol benzoate typically begins with estradiol, a naturally occurring estrogen, as the starting material. The key step involves esterification of the hydroxyl group at the C3 position of estradiol with benzoic acid or benzoyl chloride in the presence of a catalyst such as pyridine or acid chlorides under controlled conditions. The process may be carried out in organic solvents like ethanol or acetone, followed by purification steps such as recrystallisation or chromatography.

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)

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

Melting point (°C)

191

Boiling point (°C)

Degradation point (°C)

Flashpoint (°C)

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

Log P

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

Substance may enter the environment via the excreta of treated animals

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)

K_oc (mL g⁻¹)

Notes and range

Freundlich

K_f (mL g⁻¹)

K_foc (mL g⁻¹)

¹/_n

Notes and range

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

17alpha-estradiol
Note: CAS 57-91-0

Cattle

17beta-estradiol
Note: CAS 50-28-2

Cattle

estrone
Note: CAS 53-16-7

Cattle

estriol
Note: CAS 50-27-1

Cattle

ECOTOXICOLOGY

Terrestrial ecotoxicology

Property

Value

Source; quality score; and other information

Interpretation

Mammals - Acute oral LD₅₀ (mg kg⁻¹)

> 5000

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 dw soil)

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

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)

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

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

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

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)

Mammals - Acute oral LD₅₀ (mg kg⁻¹)

> 5000

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

Eliminated from the body through a two-phase process involving enzymatic hydrolysis followed by hepatic metabolism and renal excretion.

Health issues

Specific human health issues (hazard-based)

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

CLP data: known carcinogen; IARC data: known carcinogen

Handling issues

Property

Value and interpretation

General

CLP classification 2013

Health: H360, H350

WHO Classification

Not listed (Not listed)

UN Number

Not regulated

Waste disposal & packaging

Shelf-life, storage, stability and reactivity

Stable under normal temperatures and pressures

TRANSLATIONS

Language

Name

English

estradiol benzoate

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Swedish

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Dutch

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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