Praziquantel

Praziquantel	Last updated: 15/09/2025
(Also known as: biltricide; central praziquantel)

GENERAL INFORMATION

Description

An animal anthelmintic effective against gastrointestinal parasites

Examples of veterinary uses

Used to control parasitic worms including tape worms and flukes

Examples of species treated

Cats; Dogs; Fish

Approval status

VMR 2013/2033 approval status (GB/UK)

Approved - legal class and so availability varies with product and application

EU Regulatory approval status

Approved

Chemical structure

Isomerism

Praziquantel exhibits stereoisomerism, specifically enantiomerism, due to the presence of a single chiral centre at the 11b position of its pyrazinoisoquinoline structure. This means it exists as two forms: the levorotatory (L-PZQ) and dextrorotatory (D-PZQ) enantiomers. Commercial praziquantel is typically sold as a racemic mixture, containing equal parts of both enantiomers. However, pharmacological studies have shown that only the L-enantiomer is responsible for the drug’s antiparasitic activity. The D-enantiomer contributes to the drug’s bitter taste and may increase side effects without offering therapeutic benefit.

Chemical formula

C₁₉H₂₄N₂O₂

Canonical SMILES

C1CCC(CC1)C(=O)N2CC3C4=CC=CC=C4CCN3C(=O)C2

Isomeric SMILES

No data

International Chemical Identifier key (InChIKey)

FSVJFNAIGNNGKK-UHFFFAOYSA-N

International Chemical Identifier (InChI)

InChI=1S/C19H24N2O2/c22-18-13-20(19(23)15-7-2-1-3-8-15)12-17-16-9-5-4-6-14(16)10-11-21(17)18/h4-6,9,15,17H,1-3,7-8,10-13H2

2D structure diagram/image available?

Yes

Cambridge Crystallographic Data Centre diagrams

Common Name	Relationship	Link
praziquantel	-
praziquantel	-

General status

Veterinary substance type

Antiparasitic, Anthelmintic

Substance groups

Pyrazinaisoquinoline

Minimum active substance purity

Known relevant impurities

Substance origin

Synthetic

Mode of action

Though to cause parasitic paralysis leading to death. Disrupts Ca2+ homeostasis in adult worms.

Molecular targets

[Schistosome Calcium (Ca 2+) Channel]

CAS RN

55268-74-1

EC number

259-559-6

CIPAC number

US EPA chemical code

PubChem CID

Therapeutic Class

Antiparasitic products, insecticides & repellents: Anthelmintics

ATCvet Code

QP52 AA51

Controlled Drug?

Regulation 37/2010 MRL Classification

Allowed substance (Table 1: Ovine, Equidae)

Molecular mass

312.41

PIN (Preferred Identification Name)

IUPAC name

(RS)-2-(cyclohexanecarbonyl)-2,3,6,7-tetrahydro-1H-pyrazino[2,1-a]isoquinolin-4(11bH)-one

CAS name

2-cyclohexylcarbonyl-1,2,3,6,11b-hexahydropyrazino[2,1a]isoquinoline-4-one

Forever chemical

Other status information

Relevant Environmental Water Quality Standards

Physical state

Yellow to tan coloured solid

Commercial

Property

Value

Availability status

Current

Introduction & key dates

1972, first synthesised; 1980, first medical use

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

Krka d.d. Novo Mesto
Vetoquinol UK Ltd

Example products using this active

Aderexa Chewable Tablets
Bob Martin Clear 3 in 1 Flavoured Wormer
Drontal Plus Flavour Tablets

Formulation and application details

Available in a wide variety of formulations including tablets, solutions for injection, oral pastes, oral suspensions and spot-on solutions

Commercial production

The production of praziquantel typically involves a multi-step synthetic process based around constructing its pyrazinoisoquinoline core. One efficient method begins with a multicomponent Ugi reaction, which forms an acylated intermediate. This is followed by a Pictet-Spengler cyclisation, yielding the desired heterocyclic structure under mild conditions with minimal by-products like water and methanol. Another advanced approach uses flow chemistry, starting with phenylethylamine and proceeding through continuous reactions that drastically reduce production time while achieving high purity and yield.

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)

400

Moderate

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

97000

Ethanol

567000

Chloroform

Melting point (°C)

136

Boiling point (°C)

544

Degradation point (°C)

Flashpoint (°C)

255

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

2.63 X 10⁰²

Calculated

Log P

2.42

Low

Fat solubility of residues

Solubility

Data type

Density (g ml⁻¹)

1.22

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

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)

> 2840

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)

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)

> 12.2

Clarias gariepinus

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)

30.07

Daphnia magna

Moderate

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)

> 2840

Rat

Low

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

Mammals - Inhalation LC₅₀ (mg l⁻¹)

Other Mammal toxicity endpoints

Intraperitoneal LD₅₀ = 586 mg kg⁻¹

Rat

Intramuscular LD₅₀ > 2000 mg kg⁻¹

Rat

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

Excreted mainly via the urine

Health issues

Specific human health issues

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

May cause abdominal pain or cramps
Possible liver toxicant

Handling issues

Property

Value and interpretation

General

No information available

CLP classification 2013

WHO Classification

Not listed (Not listed)

UN Number

Waste disposal & packaging

Shelf-life, storage, stability and reactivity

TRANSLATIONS

Language

Name

English

praziquantel

French

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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