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Phenobarbital
Last updated: 20/03/2024
(Also known as: phenobarbitone; phenylethylbarbiturate; fenobarbitol)
GENERAL INFORMATION
Description
A barbiturate anticonvulsant veterinary drug
Availability status
Current
Introduction & key dates
-
Examples of veterinary uses
Mainly used to treat seizure, as a sedative and as an antianxiety medication
Examples of species treated
Cats; Dogs; Ferrets; Horses; Sheep
Approval status
VMR 2013/2033 approval status (GB/UK)
Approved
EU Regulatory approval status
Approved
Chemical structure
Isomerism
None
Chemical formula
C₁₂H₁₂N₂O₃
Canonical SMILES
CCC1(C(=O)NC(=O)NC1=O)C2=CC=CC=C2
Isomeric SMILES
-
International Chemical Identifier key (InChIKey)
DDBREPKUVSBGFI-UHFFFAOYSA-N
International Chemical Identifier (InChI)
InChI=1S/C12H12N2O3/c1-2-12(8-6-4-3-5-7-8)9(15)13-11(17)14-10(12)16/h3-7H,2H2,1H3,(H2,13,14,15,16,17)
2D structure diagram/image available?
Yes
Cambridge Crystallographic Data Centre diagrams
Common Name Relationship Link
phenobarbital -
General status
Veterinary substance type
Barbiturate; Anticonvulsant
Substance groups
Barbiturate
Minimum active substance purity
-
Known relevant impurities
-
Substance origin
Synthetic
Mode of action
A nonselective central nervous system depressant. It promotes binding to inhibitory gamma-aminobutyric acid subtype receptors, and modulates chloride currents through receptor channels.
Molecular targets
[Gamma-aminobutyric acid receptor subunit alpha-1, Potentiator], [Neuronal acetylcholine receptor subunit alpha-4, Antagonist], [Neuronal acetylcholine receptor subunit alpha-7, Antagonist], [Glutamate receptor 2, Antagonist], [Glutamate receptor ionotropic, kainate 2, Antagonist], [NMDA receptor, Antagonist], [Nuclear receptor subfamily 1 group I member 2, Activator]
CAS RN
50-06-6
EC number
200-007-0
CIPAC number
-
US EPA chemical code
-
PubChem CID
4763
Therapeutic Class
Antiepileptics, Barbiturates and derivatives
ATCvet Code
QN03AA02
Controlled Drug?
UK: Class B, Schedule 3; EU: UN71, Class IV
Regulation 37/2010 MRL Classification
-
Molecular mass
232.23
PIN (Preferred Identification Name)
5-ethyl-5-phenyl-1,3-diazinane-2,4,6-trione
IUPAC name
5-ethyl-5-phenyl-1,3-diazinane-2,4,6-trione
CAS name
-
Other status information
-
Relevant Environmental Water Quality Standards
-
Physical state
White crystalline powder
Formulations
Property
Product
Manufacturer
Authorisation Route
Legal Class (GB/UK)
Example products (past and present) using this active
Epiphen 30 mg Tables Vetoquinol UK Ltd UK National authorisation Prescription only medicine to be authorised by a veterinarian (POM-V)
Epityl 60mg Flavoured Tables for Dogs Chanelle Pharmaceuticals Manufacturing Ltd GB National authorisation Prescription only medicine to be authorised by a veterinarian (POM-V)
Phenoleptil 50 mg Tablets for Dogs Dechra Regulatory BV GB National authorisation Prescription only medicine to be authorised by a veterinarian (POM-V)
Formulation and application details
Available in a range of formulations including liquids for adding to feed and tablets for oral use
ENVIRONMENTAL FATE
Property
Value
Source; quality score; and other information
Interpretation
Solubility - In water at 20 °C (mg l⁻¹)
34.8
Q3 Q = Miscellaneous data from online sources
3 = Unverified data of known source
 Low
Solubility - In organic solvents at 20 °C (mg l⁻¹)
- - -
Melting point (°C)
174
Q3 Q = Miscellaneous data from online sources
3 = Unverified data of known source
 -
Boiling point (°C)
- - -
Degradation point (°C)
- - -
Flashpoint (°C)
- - -
Octanol-water partition coefficient at pH 7, 20 °C
P
2.95 X 1001 Calculated -
Log P
1.47
Q3 Q = Miscellaneous data from online sources
3 = Unverified data of known source
 Low
Fat solubility of residues
Solubility
- - -
Data type
- - -
Density (g ml⁻¹)
- - -
Dissociation constant pKa) at 25 °C
7.3
Q3 Q = Miscellaneous data from online sources
3 = Unverified data of known source
 -
-
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
1.557
Q3 Q = Miscellaneous data from online sources
3 = Unverified data of known source
 -
Environmental release
Substance may enter the environment via the faeces 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
Kd (mL g⁻¹)
- - -
Koc (mL g⁻¹)
-
Notes and range
-
Freundlich
Kf (mL g⁻¹)
- - -
Kfoc (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)
162
E4 E = Manufacturers safety data sheets
4 = Verified data
Rat		 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
- - -
- - -
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)
484
E4 E = Manufacturers safety data sheets
4 = Verified data
Pimephales promelas		 Low
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)
1460
E4 E = Manufacturers safety data sheets
4 = Verified data
Daphnia magna		 Low
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 - Acute 7 day EC₅₀, biomass (mg l⁻¹)
- - -
Algae - Acute 72 hour EC₅₀, growth (mg l⁻¹)
- - -
Algae - Chronic 96 hour NOEC, growth (mg l⁻¹)
- - -
Mesocosm study data
NOEAEC mg l⁻¹
- - -
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)
162
E4 E = Manufacturers safety data sheets
4 = Verified data
Rat		 Moderate
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
Pattern of use is unlikely to result in toxicological relevant exposure
Occupational
Pattern of use is unlikely to result in toxicological relevant exposure
Mammalian dose elimination route and rate
Eliminated mainly via kidney and faeces
Q3 Q = Miscellaneous data from online sources
3 = Unverified data of known source
 -
Health issues
Specific human health issues
Carcinogen
Genotoxic
Endocrine disruptor
?Possibly, status not identified
A0 A = Chromosome aberration (EFSA database)
0 = No data
;
B0 B = DNA damage/repair (EFSA database)
0 = No data
;
C0 C = Gene mutation (EFSA database)
0 = No data
;
D0 D = Genome mutation (EFSA database)
0 = No data
;
E3 E = Unspecified genotoxicity type (miscellaneous data source)
3 = Negative
 No data found
Reproduction / development effects Acetyl cholinesterase inhibitor Neurotoxicant
No data found No data found No data found
Respiratory tract irritant Skin irritant Skin sensitiser
No data found
✓Yes, known to cause a problem
?Possibly, status not identified
Eye irritant Phototoxicant  
No data found No data found  
General human health issues
CLP data - suspected carcinogen
Handling issues
Property
Value and interpretation
General
Combustible
Incompatible with strong oxidising substances
CLP classification 2013
Health: H360, H351, H317, H201
WHO Classification
Not listed (Not listed)
UN Number
UN2811
Waste disposal & packaging
-
Shelf-life, storage, stability and reactivity
Sensitive to prolonged exposure to light. Aqueous solutions are unstable.
TRANSLATIONS
Language
Name
English
phenobarbital
French
-
German
-
Danish
-
Italian
-
Spanish
-
Greek
-
Polish
-
Swedish
-
Hungarian
-
Dutch
-
Norwegian
-
Record last updated: 20/03/2024
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