Eprinomectin

Macrocyclic lactone Avermectin

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Cattle Topical (pour-on) 0.5 mg/kg (1 mL per 10 kg body weight) Single application Duration: Single dose; may be repeated as needed based on parasite challenge
Notes: Apply along the midline of the back from the withers to the tailhead. For optimal control, treat at the beginning of the grazing season and at intervals as recommended.
Cattle Subcutaneous 0.2 mg/kg Single injection Duration: Single dose
Notes: Administer subcutaneously in the neck or behind the shoulder. Use a sterile needle and syringe.
Sheep Topical (pour-on) 0.5 mg/kg Single application Duration: Single dose
Notes: Apply along the backline. Not approved in all countries; check local regulations.
Goat Topical (pour-on) 0.5 mg/kg Single application Duration: Single dose
Notes: Off-label use; consult a veterinarian.
Horse Oral (paste or gel) 0.2 mg/kg Single dose Duration: Single dose
Notes: Administer directly on the back of the tongue. May be repeated as needed.
Dog Oral (tablet) 0.05-0.1 mg/kg (for heartworm prevention) Monthly Duration: Year-round or as recommended
Notes: For heartworm prevention, administer once a month. For other indications, dose may vary; consult a veterinarian.
Cat Topical (spot-on) 0.5 mg/kg Monthly Duration: Monthly for heartworm prevention; single dose for other parasites
Notes: Apply to the skin at the base of the skull. Do not bathe the animal for 24 hours after application.
Rabbit Topical (spot-on) 0.5 mg/kg Single dose Duration: Single dose; may repeat in 2 weeks if needed
Notes: Off-label use; consult a veterinarian.

Clinical Indications & Species Uses

General Indications
  • Broad-spectrum antiparasitic for internal and external parasites in livestock and companion animals
Dog (Canine)
  • Treatment and control of gastrointestinal nematodes (e.g., Toxocara canis, Ancylostoma caninum, Trichuris vulpis)
  • Treatment of sarcoptic mange
  • Prevention of heartworm disease (Dirofilaria immitis)
Cat (Feline)
  • Treatment and control of gastrointestinal nematodes (e.g., Toxocara cati, Ancylostoma tubaeforme)
  • Treatment of ear mites (Otodectes cynotis)
  • Prevention of heartworm disease
Horse (Equine)
  • Treatment and control of gastrointestinal nematodes (e.g., Strongylus vulgaris, Parascaris equorum)
  • Treatment of lungworms (Dictyocaulus arnfieldi)
  • Treatment of bots (Gasterophilus spp.)
Cattle (Bovine)
  • Treatment and control of gastrointestinal roundworms (e.g., Ostertagia ostertagi, Cooperia spp., Haemonchus placei)
  • Treatment and control of lungworms (Dictyocaulus viviparus)
  • Treatment and control of eyeworms (Thelazia spp.)
  • Treatment and control of grubs (Hypoderma spp.)
  • Treatment and control of lice (Linognathus vituli, Haematopinus eurysternus)
  • Treatment and control of mange mites (Sarcoptes scabiei, Chorioptes bovis)
Small Ruminants (Sheep / Goat)
  • Treatment and control of gastrointestinal nematodes (e.g., Haemonchus contortus, Teladorsagia circumcincta)
  • Treatment and control of lungworms (Dictyocaulus filaria)
  • Treatment and control of nasal bots (Oestrus ovis)
Rabbit & Small Mammals
  • Treatment of ear mites (Psoroptes cuniculi)
  • Treatment of gastrointestinal nematodes (e.g., Passalurus ambiguus)
Exotic & Other Species
  • Treatment of mites and nematodes in various exotic species (e.g., guinea pigs, rats) - off-label use

Pharmacology & Mechanism of Action

Drug Class: Macrocyclic lactone | Pharmacological Group: Avermectin

Mechanism of Action: Eprinomectin is a macrocyclic lactone that binds selectively and with high affinity to glutamate-gated chloride channels in invertebrate nerve and muscle cells. This binding increases the permeability of the cell membrane to chloride ions, leading to hyperpolarization and paralysis of the parasite. It also interacts with other ligand-gated chloride channels, such as those gated by gamma-aminobutyric acid (GABA), but with lower affinity. The drug does not readily cross the blood-brain barrier in mammals, which contributes to its safety margin.

Pharmacodynamics: Eprinomectin exhibits potent anthelmintic and insecticidal activity against a broad spectrum of nematodes and arthropods. It is effective against both adult and larval stages of many gastrointestinal and pulmonary nematodes, as well as against external parasites such as mites and lice. Its activity is characterized by a rapid onset of action, with paralysis and death of susceptible parasites occurring within hours. The drug has a persistent effect, providing prolonged protection against reinfection for several weeks depending on the formulation and species.

⚡ Pharmacokinetics Summary

Absorption: Eprinomectin is well absorbed after subcutaneous or topical administration. In cattle, topical application (pour-on) results in systemic absorption through the skin, with peak plasma concentrations reached within 1-2 days. Oral absorption is also good but less commonly used. The extent of absorption can be influenced by the formulation and the condition of the skin.
Distribution: Eprinomectin is widely distributed throughout the body, with high concentrations found in the liver, fat, and muscle. It is highly lipophilic, which contributes to its accumulation in adipose tissue and its prolonged persistence. It is poorly distributed into the central nervous system due to the blood-brain barrier, which is a key factor in its safety in mammals.
Metabolism: Eprinomectin is extensively metabolized in the liver, primarily by oxidation and hydroxylation. The major metabolites are less active than the parent compound. In cattle, the metabolism is similar to other avermectins, with the liver being the primary site of biotransformation.
Excretion: Eprinomectin is excreted primarily in the feces as unchanged drug and metabolites. A small amount is excreted in the urine. In lactating dairy cattle, a significant portion is excreted in milk, which is why it is one of the few avermectins approved for use in lactating dairy cattle with zero milk withdrawal time.
Half-Life: The elimination half-life in cattle is approximately 2-3 days after subcutaneous injection, but can be longer after topical administration due to slow absorption from the skin. In other species, the half-life may vary; for example, in dogs it is approximately 1-2 days.
Bioavailability: The bioavailability after subcutaneous injection is nearly 100%. After topical administration, bioavailability is approximately 30-50% due to incomplete absorption through the skin.
Protein Binding: Eprinomectin is highly protein-bound, with approximately 99% bound to plasma proteins in cattle.

Available Formulations & Strengths

Topical Solution (Pour-on) 5 mg/mL (Topical)
Injectable Solution 10 mg/mL (Subcutaneous)
Oral Paste 0.5% (5 mg/g) (Oral)
Oral Tablet 50 mg, 100 mg, 200 mg (Oral)
Spot-On Solution 10 mg/mL (Topical)

Contraindications & Clinical Warnings

Contraindications:
  • Hypersensitivity to eprinomectin or other avermectins
  • Do not use in dogs and cats that are under 6 weeks of age (safety not established)
  • Do not use in cattle producing milk for human consumption if the product is not approved for lactating dairy cattle (some formulations are not approved for dairy)
  • Do not use in horses intended for human consumption (in some countries)
  • Do not use in animals with known liver dysfunction (caution)
  • Do not use in severely debilitated animals (caution)
Warnings & Clinical Precautions:
  • Keep out of reach of children and pets
  • Avoid contact with skin and eyes; wash hands after handling
  • Do not use in animals with known hypersensitivity to avermectins
  • Use with caution in animals with compromised liver function
  • In cattle, do not treat animals within 3 weeks of slaughter if using pour-on formulation (check label)
  • For topical use, do not apply to broken skin or areas with heavy mud or manure
  • In dogs, use with caution in breeds sensitive to ivermectin (e.g., Collies) as they may also be sensitive to eprinomectin; monitor for signs of toxicity
  • Do not use in puppies/kittens under 6 weeks of age
  • In lactating dairy cattle, use only products specifically approved for zero milk withdrawal
  • Avoid use in animals with severe systemic disease
  • Do not use in birds or poultry as safety and efficacy are not established

Adverse Effects & Reactions

Common:

  • Transient local irritation at injection site
  • Mild salivation (especially in horses after oral administration)
  • Slight decrease in appetite
  • Lethargy (rare)

Serious / Severe:

  • Neurotoxicity (ataxia, tremors, seizures, coma) - especially in animals with compromised blood-brain barrier or in ivermectin-sensitive breeds
  • Anaphylactic reactions (rare)
  • Hepatotoxicity (rare)

Rare:

  • Allergic skin reactions
  • Bone marrow suppression (reported in overdose)
  • Death (in severe overdose or in sensitive animals)

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
P-glycoprotein inhibitors (e.g., ketoconazole, itraconazole, cyclosporine) May increase eprinomectin concentrations in the brain, leading to neurotoxicity High
Other macrocyclic lactones (e.g., ivermectin, moxidectin) Additive toxicity; avoid concurrent use High
GABAergic drugs (e.g., barbiturates, benzodiazepines) Potential additive central nervous system depression Moderate
Organophosphates (e.g., chlorpyrifos) Potential for additive toxicity; avoid concurrent use Moderate

Overdose & Toxicity Management

Signs of Toxicity:

  • Ataxia
  • Tremors
  • Mydriasis
  • Depression
  • Salivation
  • Vomiting (in dogs and cats)
  • Seizures
  • Coma
  • Respiratory failure

Emergency Treatment Protocol: There is no specific antidote. Treatment is symptomatic and supportive. In cases of recent oral ingestion, induce emesis (if safe) and administer activated charcoal. Provide intravenous fluids, respiratory support, and control seizures with diazepam or barbiturates. Monitor vital signs and neurological status. In severe cases, consider lipid emulsion therapy (off-label) to enhance elimination of lipophilic drugs.

Food Animal Withdrawal Times

🥩 Meat: 0 days🥛 Milk: 0 days

Eprinomectin is approved for use in lactating dairy cattle with zero milk withdrawal when used as a pour-on at the label dose. For meat, the withdrawal time is 0 days for cattle when used as a pour-on. However, for injectable formulations, the meat withdrawal time may be longer (e.g., 15 days) depending on the product. Always follow label instructions. For sheep and goats, withdrawal times may vary; consult local regulations.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature, 20-25°C (68-77°F), with excursions permitted between 15-30°C (59-86°F)

Light Sensitivity: Light-sensitive — protect from direct exposure.

Handling & Special Conditions: Protect from light. Keep container tightly closed. Do not freeze. Store in a dry place.

Dispensing Status: Over-The-Counter (OTC)

Approval Status: Approved for use in cattle (pour-on and injectable) and sheep (pour-on) in the US. Not approved for dogs, cats, or horses, but may be used off-label.

Extra-Label (Off-Label) Use: In the United States, eprinomectin is available over-the-counter for cattle and sheep. Extra-label use in other species (e.g., dogs, cats, rabbits) is permitted under the Animal Medicinal Drug Use Clarification Act (AMDUCA) only with a valid veterinarian-client-patient relationship. For food animals, extra-label use requires a withdrawal period established by the veterinarian, and use in non-approved species is prohibited if it results in violative residues.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Eprinomectin is a broad-spectrum antiparasitic agent that is particularly valuable in cattle due to its zero milk withdrawal time, making it ideal for use in lactating dairy cows. It is effective against a wide range of internal and external parasites, including nematodes, mites, and lice. In companion animals, it is used off-label for heartworm prevention and treatment of certain parasites, but caution is advised in breeds sensitive to ivermectin (e.g., Collies) due to potential cross-sensitivity. For optimal efficacy, ensure accurate dosing based on body weight and administer as directed. In cattle, pour-on application should be made to clean, dry skin for best absorption. Regular monitoring for parasite resistance is recommended, and rotation with other anthelmintic classes may be necessary. Always follow label instructions and consult a veterinarian for off-label use.

References & Literature

  • 📚 Plumb's Veterinary Drug Handbook
  • 📚 Papich Veterinary Pharmacology and Therapeutics
  • 📚 Compendium of Veterinary Products (CVP)