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Niclosamide (Ref: ENT 25823 )
Last updated: 16/09/2025
(Also known as: clonitralide)
GENERAL INFORMATION
Description
A largely obsolete antiparasitic control agent for humans and animals
Examples of veterinary uses
Used for treating tape worm infections. Also used to control aquatic pests (Aquatic snails; Sea lamprey)
Examples of species treated
Horses; Ruminants; Cats; Dogs; Sheep; Poultry; Aquatic situations
Approval status
VMR 2013/2033 approval status (GB/UK)
Not approved
EU Regulatory approval status
Not approved
Chemical structure
Isomerism
None
Chemical formula
C₁₃H₈Cl₂N₂O₄
Canonical SMILES
C1=CC(=C(C=C1[N+](=O)[O-])Cl)NC(=O)C2=C(C=CC(=C2)Cl)O
Isomeric SMILES
-
International Chemical Identifier key (InChIKey)
RJMUSRYZPJIFPJ-UHFFFAOYSA-N
International Chemical Identifier (InChI)
InChI=1S/C13H8Cl2N2O4/c14-7-1-4-12(18)9(5-7)13(19)16-11-3-2-8(17(20)21)6-10(11)15/h1-6,18H,(H,16,19)
2D structure diagram/image available?
Yes
Cambridge Crystallographic Data Centre diagrams
Common Name Relationship Link
niclosamide -
General status
Veterinary substance type
Anthelmintic, Antiparasitic, Nematicide
Substance groups
Chloronitrophenol molluscidie
Minimum active substance purity
>96%
Known relevant impurities
-
Substance origin
Synthetic
Mode of action
Respiratory & stomach action. Acts by uncoupling oxidative phosphorylation in the tapeworm
Molecular targets
[DNA, Antagonist], [Oxidative phosphorylation, Uncoupler], [Glucose uptake, Inhibitor]
CAS RN
50-65-7
EC number
200-056-8
CIPAC number
599
US EPA chemical code
-
PubChem CID
4477
CLP index number
No data found
Therapeutic Class
Antiparasitic products, insecticides & repellents: Anthelmintics
ATCvet Code
QP52AG03
Controlled Drug?
No
Regulation 37/2010 MRL Classification
-
Molecular mass
327.12
PIN (Preferred Identification Name)
5-chloro-N-(2-chloro-4-nitrophenyl)-2-hydroxybenzamide
IUPAC name
2'5-dichloro-4'-nitrosalicylanilide
CAS name
5-chloro-N-(2-chloro-4-nitrophenyl)-2-hydroxybenzamide
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
Yellow-grey coloured crystalline solid
Related substances & organisms
Commercial
Property
Value
Availability status
-
Introduction & key dates
1953, discovery; Early 1960s, start of global approvals; 1977, WHO Essential medicines status
Example manufacturers & suppliers of products using this active now or historically
  • Bayer CropScience
Example products using this active
  • Bayluscid
  • Bayluscide
Formulation and application details
Available in a variety of formulations for oral administration as a veterinary treatment and as an emulsifiable concentrate for aquatic use.
Commercial production
Niclosamide is synthesised through a straightforward condensation reaction. The process begins with 5-chlorosalicylic acid and 2-chloro-4-nitroaniline, which are dissolved in chlorobenzene and heated. To facilitate the coupling, phosphorus trichloride is added dropwise, acting as a dehydrating agent to promote amide bond formation. After stirring the reaction mixture is cooled, and the resulting solid, N-(2-chloro-4-nitrophenyl)-5-chloro-2-hydroxybenzamide, is filtered and washed. The crude product is then purified by recrystallization from solvents like ethyl acetate or acetone, yielding niclosamide.
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)
5.0
F4 F = U.S. EPA ECOTOX database / U.S. EPA pesticide fate database / Miscellaneous WHO documents / FAO data, IPCS INCHEM data (US EPA Databases Related to Pesticide Risk Assessment )
4 = Verified data
 Low
Solubility - In organic solvents at 20 °C (mg l⁻¹)
- - -
Melting point (°C)
224
F4 F = U.S. EPA ECOTOX database / U.S. EPA pesticide fate database / Miscellaneous WHO documents / FAO data, IPCS INCHEM data (US EPA Databases Related to Pesticide Risk Assessment )
4 = Verified data
 -
Boiling point (°C)
- - -
Degradation point (°C)
208
L3 L = Pesticide manuals and hard copy reference books / other sources
3 = Unverified data of known source
 -
Flashpoint (°C)
- - -
Octanol-water partition coefficient at pH 7, 20 °C
P
3.63 X 1004 Calculated -
Log P
4.56
F4 F = U.S. EPA ECOTOX database / U.S. EPA pesticide fate database / Miscellaneous WHO documents / FAO data, IPCS INCHEM data (US EPA Databases Related to Pesticide Risk Assessment )
4 = Verified data
Other data: 1.0 at pH 9.6		 High
Fat solubility of residues
Solubility
- - -
Data type
- - -
Density (g ml⁻¹)
- - -
Dissociation constant pKa) at 25 °C
5.6
F4 F = U.S. EPA ECOTOX database / U.S. EPA pesticide fate database / Miscellaneous WHO documents / FAO data, IPCS INCHEM data (US EPA Databases Related to Pesticide Risk Assessment )
4 = Verified data
 -
-
Vapour pressure at 20 °C (mPa)
8.0 X 10-08
L3 L = Pesticide manuals and hard copy reference books / other sources
3 = Unverified data of known source
 Low volatility
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
Kd (mL g⁻¹)
106
R4 R = Peer reviewed scientific publications
4 = Verified data
 Slightly mobile
Koc (mL g⁻¹)
3112
Notes and range
Literature values for sediments: Kd range 52.2-186.5 mL g⁻¹, Koc range 1742-4980 mL g⁻¹, soils=5
Freundlich
Kf (mL g⁻¹)
- - -
Kfoc (mL g⁻¹)
-
1/n
-
Notes and range
-
pH sensitivity
Yes
Fate indices
Property
Value
Source; quality score; and other information
Interpretation
GUS leaching potential index
- - -
Bio-concentration factor
BCF (l kg⁻¹)
250
E3 E = Manufacturers safety data sheets
3 = Unverified data of known source
 Threshold for concern
CT₅₀ (days)
Not available -
Known soil and groundwater metabolites

None

Other known metabolites
Metabolite name and reference
Aliases
Formation medium / Rate
Estimated maximum occurrence fraction
2,5-dichloro-4-aminosalicylanilide - Rat (Urine) -
ECOTOXICOLOGY
Terrestrial ecotoxicology
Property
Value
Source; quality score; and other information
Interpretation
Mammals - Acute oral LD₅₀ (mg kg⁻¹)
> 5000
F4 F = U.S. EPA ECOTOX database / U.S. EPA pesticide fate database / Miscellaneous WHO documents / FAO data, IPCS INCHEM data (US EPA Databases Related to Pesticide Risk Assessment )
4 = Verified data
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)
> 2000
F4 F = U.S. EPA ECOTOX database / U.S. EPA pesticide fate database / Miscellaneous WHO documents / FAO data, IPCS INCHEM data (US EPA Databases Related to Pesticide Risk Assessment )
4 = Verified data
Anas platyrhynchos		 Low
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)
0.34
F4 F = U.S. EPA ECOTOX database / U.S. EPA pesticide fate database / Miscellaneous WHO documents / FAO data, IPCS INCHEM data (US EPA Databases Related to Pesticide Risk Assessment )
4 = Verified data
Oncorhynchus mykiss		 Moderate
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)
0.2
L3 L = Pesticide manuals and hard copy reference books / other sources
3 = Unverified data of known source
Daphnia magna		 Moderate
Temperate Freshwater Aquatic invertebrates - Chronic 21 day NOEC (mg l⁻¹)
0.02
P3 P = Other non-EU, UK or US Governments and Regulators
3 = Unverified data of known source
Daphnia magna		 Moderate
Tropical Freshwater Aquatic invertebrates - Acute 48 hour EC₅₀ (mg l⁻¹)
> 0.11
F4 F = U.S. EPA ECOTOX database / U.S. EPA pesticide fate database / Miscellaneous WHO documents / FAO data, IPCS INCHEM data (US EPA Databases Related to Pesticide Risk Assessment )
4 = Verified data
Danio rerio		 Moderate
Aquatic crustaceans - Acute 96 hour LC₅₀ (mg l⁻¹)
- - -
Sediment dwelling organisms - Acute 96 hour LC₅₀ (mg l⁻¹)
1.6
F3 F = U.S. EPA ECOTOX database / U.S. EPA pesticide fate database / Miscellaneous WHO documents / FAO data, IPCS INCHEM data (US EPA Databases Related to Pesticide Risk Assessment )
3 = Unverified data of known source
Chironomus riparius 48 hr		 Moderate
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) (EC₅₀)
5.0
L3 L = Pesticide manuals and hard copy reference books / other sources
3 = Unverified data of known source
Desmodesmus subspicatus		 Moderate
Algae - Chronic (growth rate, fresh; 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)
High (class III) - -
Mammals - Acute oral LD₅₀ (mg kg⁻¹)
> 5000
F4 F = U.S. EPA ECOTOX database / U.S. EPA pesticide fate database / Miscellaneous WHO documents / FAO data, IPCS INCHEM data (US EPA Databases Related to Pesticide Risk Assessment )
4 = Verified data
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)
2000
F4 F = U.S. EPA ECOTOX database / U.S. EPA pesticide fate database / Miscellaneous WHO documents / FAO data, IPCS INCHEM data (US EPA Databases Related to Pesticide Risk Assessment )
4 = Verified data
Rat		 -
Mammals - Inhalation LC₅₀ (mg l⁻¹)
- - -
Other Mammal toxicity endpoints
Intraperitoneal LD₅₀ = 250 mg kg⁻¹
V3 V = ChemID Online Databases; Chemspider; PubChem. (ChemID )
3 = Unverified data of known source
Rat		 -
Intravenous LD₅₀ = 7.5 mg kg⁻¹
V3 V = ChemID Online Databases; Chemspider; PubChem. (ChemID )
3 = Unverified data of known source
Mouse		 -
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
May be absorbed through the skin or mucous membranes
Mammalian dose elimination route and rate
Some metabolism, metabolites and unchanged parent lost mainly via the faeces
L3 L = Pesticide manuals and hard copy reference books / other sources
3 = Unverified data of known source
 -
Health issues
Specific human health issues (hazard-based)
Carcinogen
Genotoxic
Endocrine disruptor
XNo, known not to cause a problem
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
?Possibly, status not identified
 No data found No data found
Respiratory tract irritant Skin irritant Skin sensitiser
?Possibly, status not identified
?Possibly, status not identified
 No data found
Eye irritant Phototoxicant  
✓Yes, known to cause a problem
 No data found  
General human health issues
May cause gastrointestinal problems, anorexia, irritability & alopecia
Salts may cause occular irritation
Harmful if swallowed
Handling issues
Property
Value and interpretation
General
Avoid formation of dust
IMDG Transport Hazard Class 9
CLP classification 2013
Health: H319
Environment: H400, H410
WHO Classification
U (Unlikely to present an acute hazard)
UN Number
UN3077
Waste disposal & packaging
Packaging Group III (minor danger)
Shelf-life, storage, stability and reactivity
-
TRANSLATIONS
Language
Name
English
niclosamide
French
niclosamide
German
clonitralid
Danish
-
Italian
-
Spanish
niclosamida
Greek
-
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

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