Moxidectin is a broad-spectrum antiparasitic active ingredient used in veterinary medicine in pets and livestock against external parasites (lice, mites, etc.) as well as against internal parasites (e.g. roundworms). It is not used against agricultural and household pests. It belongs to the chemical class of the macrocyclic lactones.
EFFICACY AGAINST PARASITES
Type of action: Systemic & contact broad-spectrum ectoparasiticide and endoparasiticide.
Main veterinary parasites controlled: Gastrointestinal and pulmonary roundworms, lice, mites, horn flies; myiasis by screwworms, bot flies, warble flies, etc.
Efficacy against a specific parasite depends on the delivery form and on the dose administered.
Click here for general information on features and characteristics of PARASITICIDES.
Click here to view the article in this site with the most common dosing recommendations for moxidectin used in domestic animals.
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Oral LD50, rat, acute*: 106 mg/kg
Dermal LD50, rat, acute*: >2000 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) set for animal tissues (e.g. beef, mutton pork or chicken)*:
- 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. MRL's for animal tissues may be set also for agricultural pesticides that are not approved for use on animals but are used on commodities fed to animals. A MRL may be also set in the form of an IMPORT TOLERANCE for active ingredients not approved in a particular country but approved for imported animal commodities.
Withholding periods for meat, milk, eggs, etc. depend on delivery form, dose and national regulations. Check the product label in your country.
WARNING: Dogs of some breeds do not tolerate macrocyclic lactones or other medicines (e.g. emodepside) that can cross the blood-brain barrier. They can suffer more or less serious adverse effects if treated at dose rates slightly higher than the recommended ones. Consequently dosing must be as accurate as possible. This is the case for Collies and related breeds, which have a mutation in the MDR-1 gene that affects the blood-brain barrier and makes it more permeable to such compounds than in dogs without this mutation. Besides Collies, other dog breeds have shown similar problems, although the MDR-1 mutation has not been confirmed in all of them. The breeds more affected by this mutation are (% frequency): Collie (70%), Long-haired Whippet (65%), Australian Shepherd (50%, also mini), McNab (30%), Silken Windhound (30%), English Shepherd (15%), Shetland Sheepdog (15%), English Shepherd (15%), German Shepherd (10%), Herding Breed Cross (10%). Other less affected breeds are: Old English Sheepdog, Border Collie, Berger Blanc Suisse, Bobtail, Wäller. The only way to be sure that a dog is affected or not is to test for it. As more dogs are tested it is likely that the mutation is discovered in other breeds, or that the frequencies change.
Learn more about moxidectin safety.
General information on the safety of veterinary 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
Never use products for livestock on dogs and cats unless they are explicitly approved for both livestock and pets. Pets may not tolerate livestock formulations.
It is obvious that veterinary products are not intended for and should never be used on humans!!!
MARKETING & USAGE
Decade of introduction: 1990
Introduced by: AMERICAN CYANAMID (→ FORT DODGE → PFIZER → ZOETIS)
Some original brands: CYDECTIN, PROHEART
Patent: Expired (particular formulations may be still patent-protected)
Use in LIVESTOCK: Yes, moderate
Use in HORSES: Yes, moderate
Use in DOGS and CATS: Yes, moderate
Main delivery forms:
Use in human medicine: No
Use in public/domestic hygiene: No
Use in agriculture: No
Generics available: Yes, a few
SELECTION OF COMMERCIAL BRANDS FOR PETS WITH MOXIDECTIN
- ADVANTAGE MULTI for DOGS and CATS - spot-on against FLEAS, MITES, HEARTWORMS and ROUNDWORMS - BAYER - imidacloprid + moxidectin
- ADVOCATE for DOGS and CATS - spot-on against FLEAS, MITES, HEARTWORMS and ROUNDWORMS - BAYER - imidacloprid + moxidectin
- PROHEART 6 for DOGS - injectable against HEARTWORMS and HOOKWORMS - ZOETIS - moxidectin
In livestock: Yes, cross resistance with ivermectin, very frequent in gastrointestinal roundworms of sheep, goats and cattle. There are a few reports on cattle ticks (Boophilus microplus) resistance to ivermectin likely to show cross-resistance to moxidectin. Moxidectin is often initially effective against ivermectin-resistant roundworms. But resistance to moxidectin quickly develops as well if use is not interrupted rotating to another chemical class.
Moxidectin is a macrocyclic lactones obtained from fermentation products of the soil microorganism Streptomyces cyaneogriseus. It is a derivative of the milbemycins and not of avermectins as several other macrocyclic lactones (e.g. ivermectin).
Moxidectin was discovered and developed by AMERICAN CYANAMID whose Animal Health business was taken over by FORT DODGE (WYETH) and later on by PFIZER (now ZOETIS). The original TM CYDECTIN is now marketed by different coompanies in various countries.
The difference in efficacy between moxidectin and other livestock endectocides is rather small. This probably explains why there are thousands of generic ivermectin products, and only a few moxidectin generics. Generic ivermectin was available earlier than generic moxidectin, and for most uses on livestock ivermectin is good enough.
Efficacy of moxidectin
Parasiticidal efficacy of moxidectin is quite similar to that of ivermectin.
In livestock, moxidectin is effective against the major parasitic roundworms: gastrointestinal (e.g. Haemonchus spp, Cooperia spp, Ostertagia spp, Trichostrongylus spp) and pulmonary (e.g. Dictyocaulus spp). It is also effective most mites and lice species, and against numerous myiases (e.g. those caused by screwworm flies, bot flies and warble flies) usually regardless of the delivery form (pour-on, injectable, etc).
However, at the usual therapeutic dose, moxidectin products are ineffective against livestock tapeworms and flukes, fleas, mosquitoes, horse and deer flies, stable flies and several other flying insects. Cattle horn flies are only incompletely controlled by pour-on formulations. Cattle ticks (Boophilus spp) are sufficiently controlled by pour-ons, but without knock-down effect, i.e. treated cattle need 7-10 days to become more or less tick free. Other ticks (e.g. Amblyomma spp, Hyalomma spp Dermacentor spp, Ixodes spp, Rhipicephalus spp) are not controlled at all by moxidectin products.
Some studies indicate that injectable moxidectin at the usual dose (200 mcg/kg bw) is more efficient against sheep scab mites (Psoroptes ovis) than ivermectin. A single moxidectin treatment should be enough to fully control established infestations, whereas two treatments with ivermectin are required.
In pets, moxidectin at the therapeutic dose is an effective heartworm (Dirofilaria spp) preventative and controls a few other roundworms as well (e.g. Toxocara canis, Ancylostoma spp, etc.). However, alone it is ineffective against pet tapeworms, flukes, fleas, ticks and flies.
Pharmacokinetics of moxidectin
After absorption into blood moxidectin is well distributed throughout the whole body including target organs such as the gastric and gut mucosae. The highest concentrations are found in body fat that acts as a depot from where it is progressively released to blood. Moxidectin is more lipophilic than ivermectin and consequently it is stronger deposited in body fat, which results in a higher residual effect and a longer protection against several parasites than ivermectin (by comparable delivery form and administered dose).
On sheep, the subcutaneous injection provides a significantly longer protection than the pour-on.
Mechanism of action of moxidectin
As all macrocyclic lactones moxidectin acts as agonist of the GABA (gamma-aminobutyric acid) neurotransmitter in nerve cells and also binds to glutamate-gated chloride channels in nerve and muscle cells of invertebrates. In both cases it blocks the transmission of neuronal signals of the parasites, which are either paralyzed and expelled out of the body, or they starve. It also affects the reproduction of some parasites by diminishing oviposition or inducing an abnormal oogenesis.
In mammals the GABA receptors occur only in the central nervous system (CNS), i.e. in the brain and the spinal chord. But mammals have a so-called blood-brain barrier that prevents microscopic objects and large molecules to get into the brain. Consequently macrocyclic lactones are much less toxic to mammals than to the parasites that do not have such a barrier, which allows quite high safety margins for use on livestock and pets. A notable exception to this are those dogs that carry the MDR-1 mutation previously mentioned.
Click here to view the list of all technical summaries of antiparasitic active ingredients in this site.