Halothane

Halothane	Last updated: 15/09/2025
(Also known as: fluothane)

GENERAL INFORMATION

Description

A potent inhaled anesthetic once used in veterinary medicine

Examples of veterinary uses

Used for inhalational anesthesia

Examples of species treated

Horses; Domestic animals; Mammals; Birds; Reptiles

Approval status

VMR 2013/2033 approval status (GB/UK)

Not approved

EU Regulatory approval status

Not approved

Chemical structure

Isomerism

Halothane exhibits optical isomerism due to the presence of a chiral carbon atom in its structure. The central carbon is bonded to four different substituents: bromine, chlorine, a trifluoromethyl group and a hydrogen atom. This asymmetry makes the molecule chiral, meaning it can exist as two enantiomers. In clinical practice, halothane is used as a racemic mixture, the racemic form has historically been preferred for simplicity and cost-effectiveness.

Chemical formula

C₂HBrClF₃

Canonical SMILES

C(C(F)(F)F)(Cl)Br

Isomeric SMILES

No data

International Chemical Identifier key (InChIKey)

BCQZXOMGPXTTIC-UHFFFAOYSA-N

International Chemical Identifier (InChI)

InChI=1S/C2HBrClF3/c3-1(4)2(5,6)7/h1H

2D structure diagram/image available?

Yes

Cambridge Crystallographic Data Centre diagrams

Common Name	Relationship	Link
halothane	-

General status

Veterinary substance type

Anesthesetic

Substance groups

Halogenated alkane

Minimum active substance purity

Known relevant impurities

Substance origin

Synthetic

Mode of action

Involves interactions with multiple receptor sites to interfere with synaptic transmission.

Molecular targets

[Potassium channel subfamily K member 3, Binder], [Potassium channel subfamily K member 9, Binder], [Calcium-activated potassium channel subunit alpha 1, Inhibitor], [Glutamate [NMDA] receptor subunit 3A, inhibitor], [Glutamate [NMDA] receptor subunit 3B, inhibitor], [Glutamate [NMDA] receptor subunit epsilon-1, inhibitor], [Glycine receptor subunit alpha-1, modulator], [Rhodopsin], [G protein-activated inward rectifier potassium channel 2, inhibitor], [G protein-activated inward rectifier potassium channel 1, inhibitor], [NADH-ubiquinone oxidoreductase chain 1, inhibitor], [Intermediate conductance calcium-activated potassium channel protein 4, inhibitor], [ ATP synthase delta chain, mitochondrial], [Calcium-transporting ATPase type 2C member 1], [Gamma-aminobutyric-acid (GABA) receptor subunit alpha-1], [Guanine nucleotide-binding protein G(I)/G(S)/G(O) gamma-2 subunit], [Neuropeptide S receptor]

CAS RN

151-67-7

EC number

205-796-5

CIPAC number

US EPA chemical code

PubChem CID

Therapeutic Class

Nervous system: Anaesthetics

ATCvet Code

QN01AB01

Controlled Drug?

Regulation 37/2010 MRL Classification

Molecular mass

197.38

PIN (Preferred Identification Name)

IUPAC name

2-bromo-2-chloro-1,1,1-trifluoroethane

CAS name

1,1,1-trifluoro-2-bromo-2-chloroethane

Global Governance status: Listed (✓) under

UK Poisons List Order 1972	Rotterdam Convention	Montreal Protocol
XNo The Poisons List Order 1972	XNo Rotterdam Convention	XNo Montreal Protocol
Stockholm Convention	OSPAR	EU Water Framework Directive
XNo Stockholm Convention	XNo OSPAR	XNo EU Water Framework Directive

Relevant Environmental Water Quality Standards

Forever chemical

Other status information

Physical state

Colourless volatile liquid

Commercial

Property

Value

Availability status

Introduction & key dates

1951, first synthesised

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

Merial Animal Health Ltd

Example products using this active

Halothane-Vet Inhalation Vapour Liquid

Formulation and application details

Usually supplied as a liquid from which vapours are inhaled

Commercial production

Halothane is synthesised through a halogenation process that begins with trichloroethylene, which undergoes fluorination using hydrogen fluoride in the presence of antimony(III) chloride at around 130 DegC to produce 2-chloro-1,1,1-trifluoroethane. This intermediate is then subjected to bromination at high temperatures, introducing a bromine atom to yield halothane.

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 at pH 7 (mg l⁻¹)

4070

High

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

Melting point (°C)

-118

Boiling point (°C)

50.2

Degradation point (°C)

Flashpoint (°C)

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

2.00 X 10⁰²

Calculated

Log P

2.3

Low

Fat solubility of residues

Solubility

Data type

Density (g ml⁻¹)

1.87

Dissociation constant pKa) at 25 °C

Vapour pressure at 20 °C (mPa)

4.02 X 10⁰⁷

Highly volatile. If applied directly to plants or soil, drift is a concern & mitigation is advisable

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 soil and groundwater metabolites

None

Other known metabolites

Metabolite name and reference

Aliases

Formation medium / Rate

Estimated maximum occurrence fraction

bromide

Humans (Liver)

trifluoroacetic acid

Humans (Liver)

ECOTOXICOLOGY

Terrestrial ecotoxicology

Property

Value

Source; quality score; and other information

Interpretation

Mammals - Acute oral LD₅₀ (mg kg⁻¹)

> 5680

Rat

Low

Mammals - Short Term Oral NOAEL (mg kg⁻¹ bw d⁻¹)

Mammals - Long Term (Chronic) Oral NOAEL (mg kg⁻¹ bw d⁻¹)

Birds - Acute LD₅₀ (mg kg⁻¹)

Birds - Short term dietary LC₅₀ (mg kg⁻¹ bw d⁻¹)

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)

Beneficial insects (Butterflies)

Contact

Notes

Oral

Notes

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)

High (class III)

Mammals - Acute oral LD₅₀ (mg kg⁻¹)

> 5680

Rat

Low

Mammals - Short Term Oral NOAEL (mg kg⁻¹ bw d⁻¹)

Mammals - Long Term (Chronic) Oral NOAEL (mg kg⁻¹ bw d⁻¹)

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

Mammals - Inhalation LC₅₀ (mg l⁻¹)

29.0

Rat

Other Mammal toxicity endpoints

Intravenous LD₅₀ = 129 mg kg⁻¹

Human

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

Mainly eliminated via the lungs

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

Strong respiratory depressant
May cause cardiac arrest, hypotension, respiratory arrest, cardiac arrhythmias, hyperpyrexia, shivering, nausea

Handling issues

Property

Value and interpretation

General

Non-flammable, highly volatile

CLP classification 2013

WHO Classification

Not listed (Not listed)

UN Number

Waste disposal & packaging

Shelf-life, storage, stability and reactivity

TRANSLATIONS

Language

Name

English

halothane

French

German

Danish

Italian

Spanish

halotano

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

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