Pentobarbitone

Pentobarbitone	Last updated: 16/09/2025
(Also known as: nembutal ; pentobarbital)

GENERAL INFORMATION

Description

A barbituate veterinary drug used, as the sodium salt, as euthenasia and antiseizure medication

Examples of veterinary uses

Used for euthenasia and as antiseizure medication

Examples of species treated

Dogs; Cats; Mink; Small mammals

Approval status

VMR 2013/2033 approval status (GB/UK)

Approved - usually available as a prescription only medicine to be authorised by a veterinarian (POM-V)

EU Regulatory approval status

Approved

Chemical structure

Isomerism

None

Chemical formula

C₁₁H₁₈N₂O₃

Canonical SMILES

CCCC(C)C1(C(=O)NC(=O)NC1=O)CC

Isomeric SMILES

International Chemical Identifier key (InChIKey)

WEXRUCMBJFQVBZ-UHFFFAOYSA-N

International Chemical Identifier (InChI)

InChI=1S/C11H18N2O3/c1-4-6-7(3)11(5-2)8(14)12-10(16)13-9(11)15/h7H,4-6H2,1-3H3,(H2,12,13,14,15,16)

2D structure diagram/image available?

Yes

Cambridge Crystallographic Data Centre diagrams

Common Name	Relationship	Link
pentobarbitone	-

General status

Veterinary substance type

Medicinal drug: seizure control, euthenasia

Substance groups

Barbituric acid derivative

Minimum active substance purity

Known relevant impurities

Substance origin

Synthetic

Mode of action

Binds at a distinct binding site associated with a Cl- ionopore at the GABAA receptor

Molecular targets

[Gamma-aminobutyric acid receptor subunit alpha-1, alpha2, alpha3, alpha4, alpha5 & alpha6, Potentiator], [Neuronal acetylcholine receptor subunit alpha-4 & alpha7, Antagonist], [Glutamate receptor 2, Antagonist]

CAS RN

76-74-4

EC number

200-983-8

CIPAC number

US EPA chemical code

PubChem CID

Therapeutic Class

Products for animal euthanasia: Barbituates; Antiepileptics/barbiturates and derivatives and is usually used as the sodium salt

ATCvet Code

QN51AA01; QN03AA02

Controlled Drug?

UK: Class B, Schedule 3; EU: UN71, Class III

Regulation 37/2010 MRL Classification

Molecular mass

226.27

PIN (Preferred Identification Name)

5-ethyl-5-(1-methylbutyl)-2,4,6(1H,3H,5H)-pyrimidinetrione

IUPAC name

5-ethyl-5-(1-methylbutyl)-2,4,6(1H,3H,5H)-pyrimidinetrione

CAS name

5-ethyl-5-(2-pentyl)-barbituic acid

Forever chemical

Other status information

Relevant Environmental Water Quality Standards

Physical state

Fine white, odourless powder

Related substances & organisms

pentobarbitone sodium

Commercial

Property

Value

Availability status

Current

Introduction & key dates

1864, barbituric acid synthesised; 1931, introduced vet medicine; 1980s, global authourisations & use

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

Vetoquinol UK Ltd
Alfasan Nederland B.V.
Le Vet Beheer B.V.

Example products using this active

Dolethal Solution for Injection
Euthanimal Solution for Injection
Repose Solution for Injection

Formulation and application details

Usually formulated as a solution for injection

Commercial production

Pentobarbitone is synthesised through a multi-step chemical process beginning with the alkylation of diethyl malonate using ethyl (1-methylbutyl) bromide, forming a substituted malonic ester. This intermediate is then reacted with urea in the presence of a base such as sodium methoxide in methanol, under controlled heating conditions to promote cyclisation and formation of the barbituric acid ring. The reaction mixture is distilled to remove solvents and byproducts, then cooled and acidified with hydrochloric acid to precipitate crude pentobarbitone.

Impact on climate of production and use

Published GHG data is not available for pentobarbitone. However, based on similar production processes typical of petrochemical-based pharmaceuticals, GHG emissions are likely to be between 5–15 kg CO₂e per kg of product, depending on the energy source, facility efficiency, and waste treatment protocols.

ENVIRONMENTAL FATE

Property

Value

Source; quality score; and other information

Interpretation

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

679

Moderate

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

Melting point (°C)

129.5

Boiling point (°C)

Degradation point (°C)

Flashpoint (°C)

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

1.26 X 10⁰²

Calculated

Log P

2.1

Low

Fat solubility of residues

Solubility

Data type

Density (g ml⁻¹)

Dissociation constant pKa) at 25 °C

8.11

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

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 metabolites

None

ECOTOXICOLOGY

Terrestrial ecotoxicology

Property

Value

Source; quality score; and other information

Interpretation

Mammals - Acute oral LD₅₀ (mg kg⁻¹)

170

Mouse

Moderate

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)

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)

> 2263

Danio rerio Larva

Low

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)

170

Mouse

Moderate

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

Mammals - Inhalation LC₅₀ (mg l⁻¹)

Other Mammal toxicity endpoints

Intraperitoneal LD₅₀ = 108 mg kg⁻¹

Rat

Intravenous LD₅₀ = 33 mg kg⁻¹

Rabbit

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

Hepatic metabolism mainly eliminated in the urine

Health issues

Specific human health issues

Carcinogen

Genotoxic

Endocrine disruptor

No data found

; ; ; ;

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

May induce a sedative & hypnotic effect
CNS toxicant
Possible liver and kidney toxicant

Handling issues

Property

Value and interpretation

General

Will emit toxic fumes when heated to decomposition

CLP classification 2013

WHO Classification

Not listed (Not listed)

UN Number

Waste disposal & packaging

Shelf-life, storage, stability and reactivity

TRANSLATIONS

Language

Name

English

pentobarbitone

French

German

Danish

Italian

Spanish

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Polish

Swedish

Hungarian

Dutch

Norwegian

Record last updated:	16/09/2025
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