Levamisole is an antiparasitic active ingredient used in veterinary and human medicine. In dogs, cats and livestock it is used against internal parasites (roundworms). It is not used against agricultural and household pests. It belongs to the chemical class of the imidazothiazoles.
EFFICACY AGAINST PARASITES
Efficacy against a specific parasite depends on the delivery form and on the dose administered.
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Click here to view the article in this site with the most common dosing recommendations for levamisole used in domestic animals.
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Oral LD50, rat, acute*: 286 - 1085 mg/kg (in different studies)
Dermal LD50, rat, acute*: 252 mg/kg
* These values refer to the active ingredient. Toxicity has to be determined for each formulation as well. Formulations are usually significantly less toxic than the active ingredients.
MRL (maximum residue limit) established for either beef, mutton pork or chicken meat*:
- CODEX: Yes
- EU: Yes
- USA: Yes
- AUS: Yes
* This information is an indicator of the acceptance of an active ingredient by the most influential regulatory bodies for use on livestock.
Withholding periods for meat, milk, eggs, etc. depend on delivery form, dose and national regulations. Check the product label in your country.
Learn more about levamisole safety (poisoning, intoxication, overdose, antidote, symptoms, etc.).
General safety information for antiparasitics is available in specific articles in this site (click to visit):
- General safety of antiparasitics for domestic animals
- General safety of antiparasitics for humans
- General safety of antiparasitics for the environment
It is obvious that veterinary products are not intended for and should never be used on humans!!!
MARKETING & USAGE
Decade of introduction: 1960
Introduced by: JANSSEN
Some original brands: NILVERM, RIPERCOL
Patent: Expired (particular formulations may be still patent-protected)
Use in LIVESTOCK: Yes, massive on cattle, sheep goats and pig
Use in HORSES: NO
Use in DOGS and CATS: Yes, moderate
Main delivery forms:
Use in human medicine: Yes, but withdrawn in some countries in the 2000s
Use in public/domestic hygiene: No
Use in agriculture: No
Generics available: Yes, numberless...
In livestock: Yes, worldwide in gastrointestinal roundworms in sheep, goats and cattle.
In pets: No
Levamisole is an anthelmintic (wormer) compound belonging to the chemical class of the imidazothiazoles. Levamisole is the generic low-price anthelmintic par excellence for livestock. There are virtually thousands of brands.
Tetramisole is a 50/50 mixture (i.e. a racemic mixture) of two isomers (D and L), whereby the D-isomer has no anthelmintic activity. Levamisole is the pure L isomer. Levamisole is overwhelmingly preferred: there are only very few products with tetramisole.
It is mostly used in the form of the chlorhydrate salt, sometimes as a phosphate. Since it is quite soluble in water, it can be formulated for many delivery forms: drenches, injectables, feed additives, tablets, pills, etc. This is also one of the reasons for its popularity, since other cheap anthelmintics are not that versatile (e.g. benzimidazoles). It is one of the few anthelmintics that can also be delivered as a pour-ons to livestock, although this usage is nowadays quite scarce.
Levamisole is often used in mixtures, combined with either a flukicide (e.g. closantel, triclabendazole) and/or a taenicide (e.g. praziquantel, rafoxanide) to broaden the spectrum of activity, or with other nematicides (typically benzimidazoles and/or macrocyclic lactones) to overcome resistance.
Usage in dogs and cats is significantly lower than in livestock
Efficacy of levamisole
Levamisole is highly effective against all adult roundworms borh gastrointestinal (e.g. Haemonchus spp, Cooperia spp, Nematodirus spp, Ostertagia spp, Oesophagostomum spp, Trichostrongylus spp, etc.) and respiratory (e.g. Dictyocaulus spp), as well as against larvae of several species. It is also effective against arrested larvae of a few species (e.g. Ostertagia spp), and against certain eyeworms (e.g. Thelazia spp).
Unless delivered using a slow-release device, levamisole (and tetramisole) has no residual effect. This means that a single administration will kill the parasites present in the host at the time of treatment, but it will not protect the host against re-infestations.
Besides the anthelmintic activity, levamisole also has a stimulating effect on the immune system, and it can be effective against certain tumors. This immunostimulant effect on livestock and pets is not completely elucidated. In any case it is restricted to the restoration of a depressed immune response in weak or recovering animals. But in healthy animals usually it does not increases the immune response against infectious diseases they may suffer. The immune stimulating dose is significantly lower than the anthelmintic dose. Daily treatments repeated over a long period of time can have the opposite i.e. an immunosuppressive effect. Therefore it must be handled carefully for this purpose.
Recently levamisole has also been used as a cocaine adulterant.
Levamisole was used in human medicine as an anthelmintic but has been recently withdrawn in several countries because it shows severe side effects and better and less toxic anthelmintics are available.
Pharmacokinetics of levamisole
Levamisole is quickly absorbed into the bloodstream after all usual delivery forms: injectable, drench or pour-on. It is also quickly distributed throughout the whole body, including such body fluids as the bronchial mucus and the tears. It also reaches the gut after injection.
Most administered levamisol is quickly metabolized in the liver. Only about 5% of the administered dose is excreted unchanged through urine. It is also quickly excreted, mainly through the kidneys. One day after treatment about 90% of the administered dose is already excreted.
In goats levamisole is excreted even faster, which usually requires administering a higher dose than in sheep.
After pour-on administration absorption through the skin depends a lot on the outside temperature: the hotter, the faster it is absorbed. By hot weather the risk of overdosing increases considerably.
Mechanism of action of levamisole
Levamisol acts as an acetylcholinesterase (also known as AchE) mimetic. AchE is 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). Levamisole causes a depolarisation of the ganglions and nervous cells of the worms. It also interferes with the metabolism of carbohydrates (sugars) in the worm. Within 1 to 3 hours after administration the worms are paralyzed and die or are expelled.
Click here to view the list of all technical summaries of antiparasitic active ingredients in this site.