WHO Acute Hazard classification: Not listed.

Mechanism of action of Morantel

Tetrahydropyrimidines, including morantel, act on the nervous system of the worms as inhibitors of acetylcholinesterase (also known as AchE), an enzyme that hydrolyzes acetylcholine (Ach). Ach is a molecule involved in the transmission of nervous signals from nerves to muscles (so-called neuromuscular junctions) and between neurons in the brain (so-called cholinergic brain synapses). AchE's role is to terminate the transmission of nervous signals where acetylcholine is the neurotransmitter (there are several other neurotransmitters). Inhibition of AchE massively disturbs the normal movements of the parasites.

The bottom line for the parasitic worms is that they are paralyzed and die more or less quickly, or are expelled from the gut because they cannot keep themselves attached to the intestinal wall.

Acute Toxicity and Tolerance of Morantel

  • Morantel tartrate is more soluble in water than morantel. 1 g morantel tartrate corresponds to ~595 mg morantel base.
  • LD50 acute, mice, p.o. 5000 mg/kg
  • LD50 acute, rats, p.o. 926 mg/kg (tartrate)
  • As a general rule, due to its low gastrointestinal absorption livestock and horses tolerate morantel very well.
  • Cattle tolerate up to 200 mg/kg (20x the therapeutic dose) without toxic symptoms. Daily doses of 2.5 the therapeutic dose during 2.5 weeks caused no toxic symptoms.
  • In calves, doses >110 mg/kg caused intoxication symptoms.
  • Safety index in sheep is ~20, but doses >200 mg/kg can cause fatalities (therapeutic dose is 7.5 to 15 mg/kg).
  • In horses, doses of 70 to 80 mg/kg caused mild symptoms such as light abdominal pain, tremor, dyspnea (breathlessness) and ataxia (uncoordinated movements) that start about 30 minutes after administration and resolve in less than one hours. Administration of 80 mg/kg after 24 hours fasting can cause serious intoxications and even death.

Toxic Symptoms caused by Morantel Poisoning

Most frequent intoxication symptoms are cholinergic:

  • Dyspnea (breathlessness)
  • Tachypnea (accelerated breathing)
  • Hypersalivation (drooling)
  • Defecation
  • Diarrhea
  • Vomit
  • Tremor (uncoordinated trembling or shaking movements)
  • Convulsions
  • Ataxia (uncoordinated movements)

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

  • At therapeutic doses ADRs are very seldom.
  • Morantel should not be administered to sick or otherwise weak animals.
  • A damaged gastrointestinal mucosa can enhance absorption and subsequent toxicity.
  • Morantel and piperazine have an antagonistic effect on certain parasites and should not be administered simultaneously, since one compound neutralizes the effect of the other compound.
  • Organophosphates and diethylcarbamazine are also inhibitors of acetylcholinesterase and can enhance the toxicity of morantel.
  • Morantel should not be administered together with pyrantel and/or levamisole because they have the same mechanism of action and toxicity.
  • Morantel should not be administered together with minerals because this can reduce the anthelmintic efficacy.

Antidote and Treatment of Morantel Intoxication

  • The antidote for morantel is atropine.

Pharmacokinetics of Morantel

  • Morantel is used mainly in the form of its salts: tartrate, fumarate, citrate, etc. Pharmacokinetics of each salt is slightly different.
  • After oral administration to ruminants morantel tartrate is very poorly absorbed into the bloodstream.
  • Absorbed morantel is quickly metabolized in the liver. After oral administration to cattle and goats (10 mg/kg) morantel cannot be detected in plasma (< 0.05 mcg/ml). It lactating goats morantel is not detectable in the milk. This is also the case after morantel treatment with a slow-release bolus.
  • Four days after oral administration ~17% of the dose is excreted in the urine as polar metabolites, and >70% in the feces as unchanged parent molecule.
  • It is excreted mainly in the feces in the form of the unchanged parent compound.

Environmental Toxicity of Morantel

  • Morantel breaks down quickly in the feces of animals and has neither insecticidal, nor bactericidal or fungicidal effects, which makes it quite save for the environment.
  • Morantel tartrate is only slightly toxic to fish (Cyprinus carpio >40 mg/l) and water fleas (Daphnia pulex, > 40 mg/l).
  • Nevertheless, not being used in crop pesticides, there is very little information on the environmental fate of morantel.
  • Correct use on animals it is unlikely to be detrimental for the environmental, including coprophagous insects.

Additional information

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

  • Morantel belongs to the chemical class of the tetrahydropyrimidines.
  • Morantel is scarcely used in pets.
  • Morantel is not used in human medicines.
  • Morantel is not used in crop pesticides.
  • Morantel 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 morantel.


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.