WHO Acute Hazard classification: Not listed.

Mechanism of action of Praziquantel

The molecular mode of action of praziquantel is not precisely known at present. In Schistosoma worms it seems to affect the permeability of the calcium ions in the muscular membrane. As consequence the worms are paralyzed and die. In tapeworms it seems to affect carbohydrate metabolism and to damage the worm's tegument structures. As a consequence the parasites cannot avoid being digested by the gastric fluids of the host.

Acute Toxicity and Tolerance of Praziquantel

  • LD50 acute, mice, p.o. 2000-3000 mg/kg
  • LD50 acute, mice, s.c. 7000 mg/kg
  • LD50 acute, mice, i.p. >2000 mg/kg
  • LD50 acute, mice, i.m. >2000 mg/kg
  • LD50 acute, rats, p.o. 2000-3000 mg/kg
  • LD50 acute, rats, s.c. 16000 mg/kg
  • LD50 acute, rats, i.p. 600-800 mg/kg
  • LD50 acute, rats, i.m. >1000 mg/kg
  • LD50 acute, dogs p.o. >200 mg/kg. It is not possible to determine a lethal dose >200 mg/kg after oral administration because such doses cause vomit.
  • LD50 acute, dogs: s.c. >3000 mg/kg
  • Praziquantel has a hIgh safety margin (~40). Usually dogs, cats and livestock tolerate praziquantel very well.
  • Puppies 4 to 5 weels old tolerated oral or parenteral doses of up to 55 mg/kg very well.
  • In dogs, daily administration of 60 to 180 mg/kg during 4 weeks cause no sings of toxicity. Parenteral doses of 200 mg/kg caused transient vomit, salivation (drooling) and/or depression.
  • In cats, parenteral administration of 50 to 100 mg/kg caused ataxia (uncoordinated movements) and depression. Parenteral doses of 200 mg/kg were fatal.
  • In birds praziquantel overdose is toxic for the liver. Injectable praziquantel is fatal for finches.

Toxic Symptoms caused by Praziquantel poisoning

Most frequent intoxication symptoms are:

  • Salivation (drooling)
  • Depression
  • Vomit
  • Ataxia (uncoordinated movements)

Praziquantel Side Effects, Adverse Drug Reactions (ADRs) and Warnings

  • After subcutaneous injection pain can develop at the injection site. Therefore it is recommended not to inject more than 3 ml at the same injection site.
  • After oral administration therapeutic doses can occasionally cause vomit, diarrhea and anorexia (loss of appetite) in dogs, and diarrhea and vomit in cats.
  • Undesired side effects such as vomit, salivation, diarrhea and anorexia are more frequent in dogs and cats after parenteral administration. Other symptoms such as weakness, drowsiness and ataxia (uncoordinated movements) have also been reported after parenteral administration.
  • In horses treatment of massive tapeworm infections with praziquantel can cause an anaphylactic reaction 8 to 12 hours after administration. The can result in colic, gas expulsion and diarrhea that resolves about 48 hours later. In is assumed that it is caused by the massive release of allergens after rupture of the parasites' teguments.
  • Praziquantel shall not be administered to puppies less than 4 weeks old and kittens less than 6 weeks old.
  • Frequent combinations of praziquantel with febantel and/or pyrantel in dogs and cats are not antagonistic and do not show incompatibility problems.
  • The same applies to the combination of praziquantel with levamisole in sheep.
  • The simultaneous administration of praziquantel and dexamethasone can reduce the plasma levels of praziquantel.
  • Never use tablets (or suspensions, pastes, etc.) for dogs on cats, or tablets for large dogs on small dogs. It happens that some users want to save money buying large tablets for treating smaller dogs (or even cats!) twice or more times. The risk of overdosing is considerable, either due to erroneous calculations or to unskilled manipulation. In addition, dog medicines may sometimes contain ingredients that are toxic to cats.
  • Unless prescribed by a veterinary doctor, never use on dogs or cats products for livestock that are not explicitly approved for such use. There is a high risk of overdosing or of adverse drug reactions due to ingredients that are not tolerated by pets or are even toxic to them.

Antidote and Treatment of Praziquantel Intoxication

  • There is no antidote for praziquantel poisoning.
  • Treatment consists in preventing further exposure together with supportive and symptomatic measures.

Pharmacokinetics of Praziquantel

After oral or parenteral (injection) administration, praziquantel is quickly and almost completely absorbed into the bloodstream in all species. Maximum plasma levels are reached 30 to 120 minutes after administration in dogs, 2 hours after administration in sheep. It is also quickly distributed throughout the whole body: highest concentrations are found in the liver and the kidneys. It is partly released back to the gut lumen, which makes it effective against parasitic stages in the intestinal wall.

Praziquantel is quickly metabolized to ineffective metabolites. Half-life in plasma is about 30 minutes, i.e., the anthelmintic effect is rather brief and hence it's lack of residual effect.

Excretion is accomplished 40 to 70% through urine, the rest through bile and feces, almost completely in the form of its metabolites. Less than 1% is excreted unchanged. Excretion half-life in dogs and sheep is 2 to 3 hours. Twenty-four hours after treatment 80% of the administered dose has been excreted, 48 hours after treatment excretion is complete.

Environmental Toxicity of Praziquantel

  • Not being used in crop pesticides or in public hygiene, knowledge on its environmental fate and impact is very scarce.
  • Nevertheless, it can be assumed that correctly used in dogs, cats and livestock praziquantel is unlikely to be detrimental for the environment, including coprophagous insects.

Additional information

Click here for a list and overview of all safety summaries of antiparasitic active ingredients in this site.

  • Praziquantel belongs to the chemical class of the isoquinolines.
  • Praziquantel is scarcely used in livestock.
  • Praziquantel is used in human medicines.
  • Praziquantel is not used in crop pesticides.
  • Praziquantel is not used in public or domestic hygiene as a biocide.
  • Click here for General safety of antiparasitics for domestic animals.
  • Click here for General safety of antiparasitics for humans.
  • Click here for General safety of antiparasitics for the environment.
  • Click here for technical and commercial information on praziquantel.


If you intend to use a veterinary drug containing this active ingredient you must carefully read and follow the safety instructions in the product label.  Always ask your veterinary doctor, or pharmacist, or contact the manufacturer. Be aware that the safety instructions for the same veterinary medicine may vary from country to country.

The information in this page must not be confused with the Materials and Safety Datasheets (MSDS) officially issued by manufacturers for active ingredients and many other chemicals. MSDSs target safety during manufacturing, transport, storage and handling of such materials. This safety summary is a complement to the information on product labels and MSDS.

The toxicity of an active ingredient must not be confused with the toxicity of finished products, in this case parasiticidal drugs or pesticides. Finished products contain one or more active ingredients, but also other ingredients that can be relevant from the safety point of view.

All information in this site is made available in good faith and following a reasonable effort to ensure its correctness and actuality. Nevertheless, no this regarding guarantee is given, and any liability on its accuracy, integrity, sufficiency, actuality and opportunity is denied. Liability is also denied for any possible damage or harm to persons, animals or any other goods that could follow the transmission or use of the information, data or recommendations in this site by any site visitor or third parties.